Conference 7.286::space

From:	US1RMC::"[email protected]" "Ron Baalke"  1-JUN-1993 
To:	[email protected]
CC:	
Subj:	More on Comet-Jupiter Collision Possibility"

                          COMET SHOEMAKER-LEVY (1993e)

     According to IAU Circular 5807, A. Carusi has confirmed that the
center of the comet train for Comet Shoemaker-Levy (1993e) will
collide with Jupiter in 1994 during the period of July 23-27.  This
confirmation is based on the orbital elements published in IAU
Circular 5800.  He also suggests that the the entire comet train may
be involved with the collision since the window for the collision is
30 times the length of the comet train.  Donald Yeomans and Paul
Chodas from JPL have computed that the probability of the center of
the comet train colliding with Jupiter in July 1994 is as high as 64
percent. 

     IAU Circular 5807 also reports that J. Scotti from the Lunar and
Planetary Lab has recovered Comet Shajn-Schaldach, designated as 1993k. 

     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [email protected]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The tuatara, a lizard-like
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | reptile from New Zealand,
|_____|/  |_|/       |_____|/                     | has three eyes.

Article: 39934
Newsgroups: sci.space,sci.astro
From: [email protected] (Dave Tholen)
Subject: Re: Comet Shoemaker-Levy 9 at Jupiter
Sender: [email protected]
Organization: Institute for Astronomy, Hawaii
Date: Wed, 28 Jul 1993 06:52:03 GMT
 
Dave Michelson writes:
 
> Maclean's (Canada's weekly newsmagazine) ran a piece on 
> Comet Shoemaker-Levy 9 in the August 2, 1993 issue (p. 43).
> 
> Highlights:
> 
> * "an American spacecraft, the Galileo, that is due to reach Jupiter in
>    1995, will be in a position from which it can record the event next
>    July."
 
Atmospheric entry is almost precisely on the limb of Jupiter as seen from
Galileo, though the uncertainty in the position is still a few degrees.
 
Voyager 2 will have a direct view nearly centered, while Voyager 1 will
be able to view it near the limb.  Jupiter currently subtends only two
pixels, however.  I understand that they are looking into the possibility
of reactivating the Voyager cameras for this event, but the main difficulty
is in reassembling the team of people who knew how to run those systems.
 
Jupiter will be in conjunction with the Sun as viewed from Mars Observer.

Article: 71689
From: [email protected] (Ron Baalke)
Newsgroups: sci.space,sci.astro,alt.sci.planetary
Subject: Re: Voyager and SHoemaker Levy.
Date: 3 Sep 1993 15:49 UT
Organization: Jet Propulsion Laboratory
 
In article <[email protected]>, [email protected] (Pat) writes...

>Rumour has it that Voyager may be able to image the shoemaker
>Levy impact string at Jupiter.
> 
>Anyone know more?
 
JPL is looking into that possibility.  Both Voyagers will be in position
to view the collision between the comet and Jupiter.  Voyager 1 will be
about 52 AU from Jupiter and can view the impact on the planet's limb.
Voyager 2 will be closer (41 AU) and is in better position for viewing
the impact.  If Voyager is used to image to event, I think only one
spacecraft would be used, and it would most likely be Voyager 2.

     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [email protected]
    | | | |  __ \ /| | | |     Jet Propulsion Lab | 
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Nobody notices when things
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | go right.
|_____|/  |_|/       |_____|/                     | 

Article: 43212
Newsgroups: sci.astro
From: [email protected] (Gareth Williams)
Subject: Periodic Comet Shoemaker-Levy 9
Sender: [email protected]
Organization: Smithsonian Astrophysical Observatory, Cambridge, MA,  USA
Date: Wed, 15 Sep 1993 20:36:31 GMT
 
Steve Krenek wrote:
 
> We hear that next July that comet Shoemaker-Levy will plunge into the far
> side of Jupiter.
> My question is this: what organisation made this prediction, and on what
> observable evidence?
> And, what is the expected accuracy of the calculations, and hence the
> probability of the event actually occurring?
 
Dave Tholen responded:
 
> Comet P/Shoemaker-Levy 9, to be specific.  There are several other comets
> named Shoemaker-Levy.
> Several organizations have confirmed this prediction, including the Jet
> Propulsion Laboratory and the Minor Planet Center.  The evidence is the
> accumulation of ground-based astrometry.
> The accuracy of the calculations is quite high.  The formal probability
> of the event happening exceeds 99 percent.
 
There are 11 other comets that bear the name Shoemaker-Levy, 8 of
which are periodic. 

Re the initial prediction that P/S-L 9 would hit Jupiter, credit where
credit is due: 
 
The first indication of a very close approach to Jupiter in 1992 (the
event that presumably split the comet) was by B. G. Marsden, SAO (see
IAUC 5744).  The first indication that the 1994 perijove might be
comparably close came from independent calculations by S. Nakano (in
Japan) and Marsden, and in late April Nakano was the first to suggest
that an impact might occur.  By May 22, the calculations by Marsden
and Nakano were refined to the point where the possibility of impact
was worth mentioning on IAUC 5800.  This Cicular also mentioned work
done by A. Carusi (Rome) who confirmed the general scenario described
by Marsden and Nakano. Calculations by D. Yeomans and P. Chodas (JPL)
indicating a probability "as high as 64 percent" appeared on IAUC
5807, even though privately they were saying nearly 100 percent.  The
calculations by Marsden, Nakano, Carusi and Yeomans & Chodas used
different models for the solar system and the amount of agreement
between the various predictions is excellent. 
 
Calculation of the final impact details will depend on calculating
orbits for the individual nuclei. 
 

    The next reply is a very interesting, but fairly long, report on the
    proceedings of a workshop on Comet Shoemaker-Levy 9.

    The report is 320 lines long, so DECwindows users should expect
    some load-time delay.

    Regards,

    John B.

This is taken from the Comet Shoemaker-Levy BBS public account at
pdssbn.astro.umd.edu (usr name c1993e) with permission of Jay Melosh,
one of the organizers of the Comet Crash Bash meeting. The file
name is workshops/UAZ_proceedings.  I am posting it here since I
was asked to provide a summary bye some members of this group
and to offload the server a bit.  The  server is ment for people
actively working on the comet impact problem.  Please be considerate.
---


Report on the "Comet Pre-Crash Bash"  by H. J. Melosh.        20
September 1993

The imminent impact of periodic comet Shoemaker-Levy 9 with Jupiter has
generated a tremendous amount of excitement within the scientific
community.  On Monday and Tuesday, 23 and 24 August, 1993 more than 120
scientists from all over the United States gathered for an impromptu
"brain-storming" workshop at the Lunar and Planetary Laboratory of the
University of Arizona in Tucson, Arizona.  The workshop was convened by
H. J. Melosh, and attendance from outside Tucson was impressively
heavy, in spite of only 2 weeks notice of the meeting.

The workshop's format featured a number of invited speakers followed by
long periods for general discussion and unscheduled presentations by
participants.  As it happened, discussion was lively and many ideas
were exchanged between observers and theoreticians.  This report can
only outline the highlights.

The scientific portion of the meeting was opened by Carolyn Shoemaker,
who described the discovery of the comet by her, Gene Shoemaker and
David Levy at the Mount Palomar Observatory in California on 26 March
1993.  Carolyn first recognized the comet as a strange wisp in her
microscopic stereo comparator.  Accustomed to the appearance of comets,
she was puzzled by the linear form of the coma.  It looked like a
galaxy on edge--except that its apparent elevation above the background
in stereo indicated that it had moved substantially between exposures
of the two plates.  Not knowing just what to make of the object, which
Carolyn described as a "squashed comet", the discoverers called Jim
Scotti, who was observing with the Spacewatch telescope on Kitt Peak,
Arizona.  Scotti imaged the object with the 91 cm telescope and
revealed the "string of pearls" appearance of the multiple nuclei.  It
was then clear that a most unusual comet had been found.  Carolyn
brought the discovery plates and comparator to the workshop, and nearly
all the participants experienced the thrill of viewing the first image
themselves.

Jim Scotti described his experiences in observing the comet, along with
the discovery that, not only was the comet in orbit about Jupiter, but
that it was targeted to impact the planet about 21 July next year.
Orbital computations performed by Brian Marsden, based partly on
Scotti's observations, show that it passed within about 1.6 RJ of
Jupiter on about 8 July 1992, well within the Roche limit (about
2.7RJ), where tidal forces exceed self gravity.  Scotti described work
he did with H. J. Melosh in modeling the tidal breakup of
Shoemaker-Levy 9's progenitor, which produced a close fit to the
observed chain orientation (which is at a substantial angle to the
orbit direction) and resulted in a predicted progenitor diameter of
only about 2 km.  Tidal stresses at closest approach were only about
10^-4 bar for such a comet, suggesting that it was initially only a
loose aggregation of negligible strength, held together by its own self
gravity.  The tidal breakup model was used to predict the future
evolution of the chain, with the result that all of the fragments
should hit Jupiter at about the same latitude and longitude with
respect to the dawn terminator.  Scotti also emphasized that the comet
is accompanied by considerable quantities of dust that extends in
slightly canted "wings" beyond the end of the visible nuclei.  No
discrete nuclei have been found in these dust bands, and it is unclear
exactly what their dynamical relation to the comet might be.

Scotti's presentation generated considerable discussion.  The geometric
relations of the sun, Jupiter and the dust bands were obscure to most
participants, and some lively discussion ensued.  Many questions were
asked about the size estimate, and Z. Sekanina reported work done at
JPL by D. Yeomans and P. Chodas on similar breakup models.  The
Scotti-Melosh model neglects cometary rotation and self-gravity of the
fragments, and Sekanina argued that rotation might change the detailed
results, although he agreed that the parent comet could not have been
more than a few km in diameter.  Luke Dones noted that he had computed
a similar tidal breakup model that includes self-gravity of the
fragments and found that its inclusion made little difference to the
results.  Discussion also centered on the origin of the dust bands,
with many participants concluding that the dust is being shed by a
large number of meter-plus diameter boulders spread out beyond the ends
of the chain of discrete nuclei.  No mechanism for the dispersion of
this dust was agreed upon.

Hal Weaver then described the results of several Hubble Space Telescope
exposures of the comet.  Hubble was unable to resolve the individual
nuclei, and an upper limit of 5 km was placed on their diameters.  Most
of the brightness in these images is due to dust in the coma.  No OH
emission, or any other molecular emission, has yet been detected-- the
spectrum seems to be a red-scattered solar spectrum.  This observation
triggered a lively debate about whether S-L 9 is a comet or an
asteroid.  Although some OH emission might be expected from the
exposure of amorphous ice upon breakup, the final consensus was that
even a water-rich comet would not be expected to show detectable OH
emission at 5 AU from the sun.  It was stated than no comet has shown
OH farther than 3.3 AU from the sun, and that the absence of emission
lines does not imply that S-L 9 is not a comet.

Torrance Johnson then described observational opportunities from
spacecraft.  Although the predicted impact point is not visible from
Earth, the Galileo spacecraft happens to be in an orbit from which the
impacts will be visible.  Although Galileo is too far from Jupiter to
get good images of the impacts themselves (the disk of Jupiter will be
60 pixels across from Galileo, so the impact sites will occupy only one
pixel), good data should be obtained on integrated IR and visible light
emission as a function of time, even for the most pessimistic estimates
of nucleus size.  Galileo instruments should also be able to record
radio emissions associated with comet/magnetosphere interactions.  An
important issue was obtaining good predictions of the impact times far
enough (days to weeks) in advance to allow optimum use of the limited
recorder space and slow downlink data rate.  Johnson further discussed
the intriguing possibility of using the Voyager 2 spacecraft to view
the impacts.  Although resolution is very poor (2 pixels across the
disk), Voyager 2 would look almost directly down over the impact site,
and the integrated data thus collected might be very useful.  Johnson
noted that it is very convenient that there will be 20-odd impacts over
6 days, because if brightness estimates are initially poor and the
first exposures are not set correctly, there will be multiple
opportunities to correct them for later impacts.

After a further discussion period, during which several participants
urged that more consideration be given to Jupiter's thermal
perturbation of the comet during its close pass last year (both
mechanical spallation effects  and the possibility of volatile
evaporation were suggested), Gene Shoemaker presented his recent work
on the orbital history of S-L 9 and other comets with similar orbits.
He noted that, besides S-L 9, other Jupiter family comets have
apparently spent time as temporary satellites of Jupiter, although none
has previously been caught in this condition.  Comets Gehrels 3 and
Helin-Roman-Crockett, when their orbits are integrated backward, once
made several loops about the planet and in the future both will
experience additional temporary capture episodes.  Most such objects
evidently enter orbit through the L1 point, then exit sometime later
through L2 whence they take up heliocentric orbits similar to Jupiter's
orbit.  It is nevertheless rare that one of these objects makes a pass
inside the Roche limit.  He estimated that at any given time there is a
steady state population of about 1 comet of diameter > 2 km in orbit
about Jupiter, and that Jupiter can capture a comet about once a
century.  He also described attempts to find pre-discovery images of
S-L 9's parent (pre-close encounter) comet.  Although plates of the
appropriate region exist, so far none have revealed the comet,
suggesting that it may have been too faint.  However, efforts to find
images of the parent are continuing.

The next segment of the workshop focused on the physical effects of the
impact on Jupiter.  Z. Sekanina opened this discussion by describing
his work on the tidal breakup of a comet passing within the Roche limit
and emphasized the low strength implied.  He then described the flight
of the projectile through Jupiter's atmosphere in terms of models
originally developed to model meteors in Earth's atmosphere.  He
emphasized the importance of ablation effects and the possibility of
intermediate flare-ups before the final episode of energy deposition.
He attempted to estimate light curves and showed several examples from
terrestrial meteors, illustrating the complexity of the observed
curves.

Kevin Zahnle described his work on energy deposition of entering
comets, following up on his model originally developed to model
airblasts from meteorites entering Venus' atmosphere and the 1908
Tunguska event on Earth.  He argued that the projectile would break up
as it entered, thus increasing its drag and depositing its energy in a
relatively small altitude interval.  The energy deposited would then
heat the surrounding gas, which would expand upward in a classic
fireball.  For km size projectiles, most of this energy deposition
takes place about 200 km below the upper cloud decks, and so is not
directly visible, but the fireball should become visible when it rises
back up into the upper atmosphere, about 1 minute later.  He argued
that ablation is not important for large projectiles, although what
"large" meant was debated by the participants, and he reported that a
check by Chris Chyba showed that his results changed somewhat when a
different ablation model is used.  Temperatures in the shock wave ahead
of the entering projectile were estimated to reach 30,000 K during the
high speed part of the entry.  Zahnle closed his talk by showing a
video of a numerical computation of the expansion of a fireball in a
stratified atmosphere modeling that of Jupiter.

Several participants showed results from numerical computations
currently in progress.  Tom Ahrens presented a computation using an SPH
hydrocode that followed the entry of a 10 km diameter projectile.  He
and T. Takata found that the projectile penetrated relatively deeply,
depositing most of its energy 500 km below the 1-bar level.  The impact
generated a 6 km/sec upward plume and partitioned about 70% of its
energy to atmospheric heat.  David Crawford described similar
computations that use the Sandia hydrocode CTH, although his work
mainly focused on the projectile.  It was clear that several groups are
ready to do hydrocode computations of the comet entry, but due to the
need for lengthy supercomputer runs none has yet encompassed the entire
impact process.  A major point of interest was whether any atmospheric
gasses would be ejected at high enough speed to enter space around
Jupiter and perhaps affect the radiation belts or magnetosphere.  None
of the computations presented showed such high speed jets, but it was
not clear that any of them have been carried out with sufficient
accuracy to be sure of their absence.  Other issues were the importance
of thermal radiation (not included in any of the hydrocodes) and the
need for an accurate equation of state.

Attention then turned to the longer term effects of an impact on the
atmosphere of Jupiter.  Andy Ingersoll organized his own sub-workshop
on atmospheric effects.  The presentations were lead by Dave Stevenson,
who noted that the amount of material in the comets, if reduced to fine
dust and mixed through the upper atmosphere of Jupiter, was itself
sufficient to cause albedo changes over the entire planet.  The
probability of such complete mixing was not known, however.  Andy then
addressed the question of whether the vorticity changes induced by the
rising fireball could produce structures like either the great "red" or
smaller "white" spots.  He noted that the amount of energy in one of
the smaller white ovals (10^29 ergs) is comparable to the kinetic
energy of one of the cometary fragments.  The problem is that an
undetermined amount of this energy in the rising fireball is likely to
be radiated away.  The rising fireball is also likely to inject a large
quantity of volatiles--some from the comet itself and some from
Jupiter--into the upper atmosphere.  Ingersoll and Stevenson presented
a simple analytic model of the geostrophic adjustment of the Jovian
atmosphere to a sudden heat pulse.  They concluded that some energy
would be radiated away from the heated region by gravity waves, and the
rest would remain as a circular vortex--a high-pressure weather system
some 2000 km in diameter for a 1 km diameter comet fragment.  They
predicted that in the near IR some variability of molecular adsorption
features should occur.

Tim Dowling used his Jovian general circulation model to examine the
effects of a sudden injection of heat in the atmosphere.  He found that
the result was a narrow ring of gravity waves that propagated outward
from the impact site and spread several times around the planet and
showed a video illustrating the waves' propagation.  Preexisting jet
streams in Jupiter's atmosphere destroyed the vortex that formed
immediately after the impact.  No new spots of long duration formed in
the simulation.  Dowling emphasized that a fundamental parameter of the
model, which depends on the temperatures and thickness of the Jovian
"weather layer", is only poorly known for Jupiter, but that the best
way to measure it is to determine the speed of gravity waves.  Since
the predicted waves are narrow, HST observations of Jupiter may be
required to detect them.

The first day of the workshop ended with an extended discussion of what
observations should be made.  The general feeling was that all possible
observations should be made at all possible wavelengths and at the
highest possible resolution,  but practical considerations tempered
this grandiose wish.  Heidi Hammel and others emphasized the
desirability of IR imaging in addition to spectral studies.  John
Spencer discussed the possibility of observing the flash emitted by the
entering comets by its reflection off one of Jupiter's moons.  This is
best done by observing a nearby moon while it is eclipsed by Jupiter.
John showed an ephemeris of the Galilean satellites in which it appears
that one or another satellite will be in a favorable location for a
large fraction of the time.  He also discussed the feasibility of
observing flashes reflected from Almethea and described the virtues of
using methane band filters which screen out much of Jupiter's light.

The final session of the workshop opened Tuesday morning.  Alex Dessler
gave a lively presentation on the magnetospheric effects of the comet
and its attendant dust.  He analyzed dust charging and interactions
with the magnetic field, showing that the charge on dust particles
should increase many-fold as they cross the magnetopause.  This
increases the electrostatic stress on the particles and may thus cause
them to break down into even finer dust.  This may cause the
magnetosphere itself to become temporarily visible, and provide the
first-ever image of the magnetosphere.  To do this a telescope with a
wide field of view is needed--2 deg x2 deg.  Something like a Schmidt
telescope would be ideal, with observations starting about 2 months
before impact to catch the first entry of dust into the magnetosphere.
Dessler also argued that some of the dust from the comet would not
impact the planet, but instead go into temporary orbit (the
"decapitated comet" model).  The presence of the dust might quench the
inner radiation belt  and cut off the synchrotron emission.  The
timescale for the radiation belt to reestablish itself is highly
uncertain ("bets" from participants on the timescale ranged from 30
minutes to 11 years!), but observing the effects of such a disturbance
will reveal a great deal of information on energy fluxes in this
region.  A final possibility that gave rise to much discussion centered
on whether an atmospheric "backsplash" kicked up by the comet's entry
would inject a significant amount of material into the Io torus.  If
gas is present, it will become ionized and may strongly intensi

Jay Melosh, in collaboration with Paul Schenk, made the final
presentation in which he described crater chains on Callisto and argued
that they had been made by tidally split comets like S-L 9 (although
not necessarily comets in orbit about Jupiter) that ran into Callisto
on the way out from Jupiter.  All but one of the 13 chains on Callisto
are on the Jupiter-facing hemisphere and three crater chains have been
found on the Jupiter-facing hemisphere of Ganymede.  A tidal splitting
model accounts for the observed 200-600 km lengths and linearity of the
chains, whereas a rotational splitting model would result in loops of
craters, not lines.  Melosh described a model that attempted to relate
the diameter of craters in the chain with the length of the chain using
impact crater scaling laws.  He found that to fit the data he had to
assume that either the scaling laws failed by a factor of 2, or that
the cometary fragments had densities of 0.1 gm/cm^3.  Paul Weissman
pointed out that this model was not strongly supported by the data,
which could be interpreted equally well by the supposition that all
comets were composed of a variable number of lumps of the same size,
lumps big enough to create 10 km diameter craters when they strike
Callisto.

The workshop closed with a discussion of what is worth doing.
Theoretical modelers were urged to refine their hydrocode computations
of atmospheric entry, observers were urged to start thinking about
telescope time allocations, especially for HST, and various instrument
development projects were discussed.  John Spencer suggested pooling
orders for custom filters, such as methane band filters.  Paul Weissman
urged the participants to be careful when talking to the press to avoid
over-dramatizing the impact effects visible from Earth.

During the workshop a FAXed announcement was received from Jurgen Rahe
at NASA announcing the availability of about $750,000 for observational
projects.  Morris Aizenman of NSF was present at the workshop and
announced a program of similar size to fund both theoretical and
observational studies.

The workshop adjourned at noon on Tuesday, 24 August 1993.


--
William Sears                   | 'I reserve the right to ask irrelevant  
Lunar and Planetary Lab         |  questions, even impudent ones.          
[email protected]          |  You, of course, don't have to answer.'"    

RE: <<< Note 853.6 by CXDOCS::J_BUTLER "E pur, si muove..." >>>

>David Crawford described similar computations that use the Sandia hydrocode
>CTH, although his work mainly focused on the projectile.

Hey, he's my brother in law. Neat to see him mentioned here. He got his PhD
from Brown University a year or so ago, and started working at Sandia this
past spring. He's been doing research into cratering phenomena for a few years
now, which was the focus of his doctorate work. I saw him just a few weeks ago
and he mentioned that he was writing a proposal to use the Sandia supercomputer
facilities to model the comet impact with Jupiter.
						-- Tom

Article: 46828
From: [email protected] (Dan Bruton, Texas A&M)
Newsgroups: sci.astro
Subject: Comet/Jupiter Collision FAQ
Date: 10 Nov 1993 22:14 CST
Organization: Texas A&M University OpenVMScluster
 
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *                                                                         *
 *                       Comet/Jupiter Collision FAQ                       *
 *                                                                         *
 *      The following is a list of frequently asked questions concerning   *
 *  the collision of comet Shoemaker-Levy 9 with Jupiter.  Thanks to all   *
 *  those who have responded to questions.  Contact Dan Bruton at          *
 *  [email protected] or John Harper at [email protected] with comments,       *
 *  additions, corrections, etc.                                           *
 *                                                                         *
 *                        Last updated 11-Nov-1993                         *
 *                                                                         *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 
GENERAL QUESTIONS
 
Q1.1:  Is it true that a comet will collide with Jupiter in 1994?
Q1.2:  Who discovered the comet and when?
Q1.3:  Can I see the comet with my telescope?
Q1.4:  Where can I find a GIF image of this comet?
 
SPECIFICS
 
Q2.1:  Why did the comet break apart?
Q2.2:  What does the orbit of the comet look like?
Q2.3:  How long is the fragment train?
Q2.4:  Where will the comet fragments collide on Jupiter?
Q2.5:  What will be the effect of the collision?
Q2.6:  How can I observe the collisions?
Q2.7:  Will Hubble, Galileo or Voyager be able to image the collisions?
Q2.8:  Where can I find out more information?  
 
GENERAL QUESTIONS 
 
Q1.1:  Is it true that a comet will collide with Jupiter in 1994?
 
  Yes, the shattered comet Shoemaker-Levy 9 (1993e) is expected to
collide with Jupiter over a 5.6 day period.  The first of 20 comet
fragments is expected to hit Jupiter at around 10 UT on July 18, 1994
and the last around 0 UT on July 24, 1994 [1].  The accuracy of these times
will improve as the knowledge of the orbit improves in early 1994.
 
Q1.2:  Who discovered the comet and when?
 
  Eugene and Carolyn Shoemaker and David H. Levy discovered the "squashed"
comet on March 25, 1993 on photographic plates taken on March 22, 1993. 
The photographs were taken at Palomar Mountain in Southern California
with a 0.46 meter Schmidt camera and were examined using a stereomicroscope
to reveal the comet.  James V. Scotti confirmed the comet discovery with 
the Spacewatch Telescope at Kitt Peak in Arizona [2].
 
Q1.3:  Can I see the comet with my telescope?
 
  The comet has a magnitude of about 14.  The glow of Jupiter makes 
imaging the comet difficult.  If you have a CCD camera, you should be able to
see the train of fragments with a telescope of about 20 to 25 centimeters;
a slightly larger telescope will probably be needed if you use conventional
photography.  
 
Q1.4:  Where can I find a GIF image of this comet?
 
  Some GIF images can be obtained via anonymous ftp from pdssbn.astro.umd.edu 
in the /ftp/pub/images directory.  The GIF images here are named SL9*.GIF.
Also there are a some images at ftp.cicb.fr in the /pub/Images/ASTRO/hst
directory with explanations in /pub/Images/ASTRO/hst/docs.  The GIF
images here are named 1993e*.GIF.
 
 
SPECIFICS
 
Q2.1:  Why did the comet break apart?
 
  The comet is thought to have broken apart due to tidal forces on its 
closest approach to Jupiter (perijove) in May 1992 [2].  Tidal forces are 
a result of competing gravitational force and effective centripetal force 
and is strongest at closest approach.

  Shoemaker-Levy is not the first comet to break apart.  Comet West 
shattered in 1976 near the Sun [3].  Astronomers believe that in 1886 
Comet Brooks 2 was ripped apart by tidal forces near Jupiter [2].  Furthermore,
images of Ganymede [3] show craters "lined up" which may have resulted 
from the impact of a comet similar to Shoemaker-Levy 9.
 
Q2.2:  What does the orbit of the comet look like?
 
  Shoemaker-Levy 9 is thought to have made its closest approach to Jupiter 
on May 16, 1992 at a distance of about 0.007 astronomical units from 
Jupiter [2].  The Roche limit of Jupiter is about 0.001 astronomical units. 
The comet reached apojove (farthest from Jupiter) around July 8, 1993
at at distance of about 0.33 astronomical units from Jupiter.  The orbit
looks somewhat elliptical.  See postscript images on pdssbn.astro.umd.edu
in the /ftp/pub/images directory for a visual representation.
 
Q2.3:  How long is the fragment train?
 
  The angular length of the train was about 51 arc-seconds in March 1993 [2].
The length of the train then was about one half the Earth-Moon distance.
The train is expected to lengthen to two times the Earth-Moon distance
in July 1994 (according to James Scotti at the ALPO Workshop in August 1993).
 
Q2.4:  Where will the comet fragments collide on Jupiter?
 
  All components of the comet will hit on the dark farside of Jupiter,
out of sight from Earth.  The impact sites will be around 45 degrees
South at a point roughly 35 degrees east (toward the sunrise terminator) 
from the midnight meridian.  About 1.5 hours after each hit, the impact
points will rotate into view as seen from Earth [1]. 
 
Q2.5:  What will be the effect of the collision? 
 
  The energy of collision is said to be equivalent to 100,000,000 megatons 
of TNT.  The impact of some of the fragments is expected to generate 1000 km 
high plumes.  Some suggest that if the collisions were to occur on the 
near side of Jupiter the impacts would be around -5 magnitude.
 
Q2.6:  How can I observe the collisions?  
 
  One can monitor the atmospheric changes on Jupiter using the naked 
eye (drawings) or using photography.  It is important, however, to 
observe Jupiter for several months in advance in order to know which
features are due to comet impacts and which are naturally occurring.
A video camera may be able to record real time atmospheric changes
if your telescope is big enough.  The Red Spot and other features
have been successfully recorded using a video camera and a 14"
telescope with eyepiece projection (2" eyepiece works best).

  One may be able to witness the collisions indirectly by monitoring
the brightness of the Galilean moons that may be behind Jupiter as seen
from Earth.  The program GALSAT will calculate and display the locations 
of the Galilean satellites for a given day and time and can be obtained 
via ftp from oak.oakland.edu in the /pub/msdos/astronomy directory.
One could monitor the moons using a photometer, a CCD, or a video
camera pointed directly into the eyepiece of a telescope.

  Radio emissions due to the impacts may be strong enough to 
be detected by small radio telescopes.  Someone at the Association of 
Lunar and Planetary Observers conference in August talked about this.  
The speaker suggested to listen in on 15-30 MHz during the comet impact,
but to avoid 27 MHz because this frequency is used for CB communications. 
So it appears that one could use the same antenna for both the Jupiter/Io 
phenomenon and the Jupiter/comet impact.  There is an article in 
Sky & Telescope which explains how to built a simple antenna for
observing the Jupiter/Io interaction [4].
 
Q2.7:  Will Hubble, Galileo or Voyager be able to image the collision?
 
  The Hubble Space Telescope, like earthlings, will not be able to see
the collisions but will be able to monitor atmospheric changes on Jupiter.
The telescope is scheduled for repairs in December 1993.

  The impacts will occur on the limb of Jupiter as seen from the Galileo
Space Probe. However, due to antenna troubles the data transfer rate
back to Earth is slow and as a result the onboard computer will still 
have data from the Ida (asteroid) encounter.  Either some of the Ida 
images will need to be erased or some of the Jupiter/comet observations
will need to be omitted.  

  Even though, Voyager II will have a direct view of the impacts, the probe
will be so far away that Jupiter will appear only as a pixel on the images.
This does not mean that, however, that useful data cannot be obtained
from this probe.
 
Q2.8:  Where can I find out more information?  
 
 [1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
 [2]  "Pearls on a String", David H. Levy, Sky & Telescope, July 1993, 
       page 38-39.
 [3]  Discovering the Universe, William J. Kaufmann, page 198,174.
 [4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
 [5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
 [6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
 [7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
 [8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy, 
       September 1993, page 18.
 [9]  "Jove's Hammer", Robert Burnham, Astronomy, October 1993, page 38-39.
 
ACKNOWLEDGMENTS
 
Thanks to Ross Smith ([email protected]) for starting a FAQ
and to all those who have posted answers to questions.
 
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .  
|| Texas A & M    ||                `.           .             
|| [email protected] ||               `.              ` : :        ` 
||||||||||||||||||||                                              .  
                                                                     .

>The program GALSAT will calculate and display the locations of the Galilean
>satellites for a given day and time and can be obtained via ftp from
>oak.oakland.edu in the /pub/msdos/astronomy directory. 

  Can we access this program from DEC? Anyone have good enough ftp skills pull
it across and place it into this note? I assume it's a C program but that could
be wrong, anyone know how to tell what the file name is? They just give the
program name and directory. 

  George

I tell you, Galelio is looking BAD.

In July 1994, they will still have unsent pictures from the ida encounter!!!!!

That leaves them with something less than a year to speed up transmission speed
or the mission results will be subnominal (but, sadly, still far greater than
MO)....

Tony

> Can we access this program from DEC? Anyone have good enough ftp skills pull
>it across and place it into this note? I assume it's a C program but that
>could
>be wrong, anyone know how to tell what the file name is? They just give the
>program name and directory. 

You ls the directory.  Turns out that it is galsat50.zip, implying a
zip-compressed file, who knows what is in it.  Given that the directory is
msdos/..., I assume it is a program to run on a PC.

I have it, but I don't have a public place to put it.  If someone can offer a
place for it, let me know.

Burns

It contains a text file and a DOS executable which does a nice diagram of
Jupiter, and the positions of satellites around it, as well as a graph of where
they will be in the next week, and a small picture of what it will look like in
the sky.  Kind of neat.

Burns

Article: 47770
From: [email protected] (Ron Baalke)
Newsgroups: alt.sci.planetary,sci.space,sci.astro
Subject: Re: Comet/Jupiter Collision FAQ
Date: 30 Nov 1993 05:36 UT
Organization: Jet Propulsion Laboratory
 
[email protected] (Dan Bruton, Texas A&M) writes:

>Q2.4:  Where will the comet fragments collide on Jupiter?
 
>  All components of the comet will hit on the dark farside of Jupiter,
>out of sight from Earth.  The impact sites will be around 45 degrees
>South at a point roughly 35 degrees east (toward the sunrise terminator)
>from the midnight meridian.  About 1.5 hours after each hit, the impact
>points will rotate into view as seen from Earth [1].
 
More precisely, the impact of the center of the comet train is predicted to
occur at -37 degrees Jupiter latitude at a Sun-comet-Jupiter angle of 51
degrees on the morning side of the planet. (Source: David Seal from JPL).
 
>Q2.5:  What will be the effect of the collision?
 
Kevin Zahnle from JPL predicts that each comet fragment will explode
into a fireball about 200 km below the cloudtops of Jupiter.  The
fireball will initially be hidden underneath the cloudtops but will
expand rapidly with the plume material rising to about 1.02 to 1.25
Jupiter radii above the cloudtops.  The temperature of the fireball may
reach up to 30,000 degrees C with a luminosity of 4x to 25x the brightness
of Jupiter.
 
>Q2.7:  Will Hubble, Galileo or Voyager be able to image the collision?
 
>  Even though Voyager II will have a direct view of the impacts, the probe
>will be so far away that Jupiter will appear only as a pixel on the images.
>This does not mean, however, that useful data cannot be obtained from this
>probe.
 
The comet collisions are visible from both Voyager 1 and Voyager 2.
Voyager 1 will be 52 AU from Jupiter and will have a near-limb observation
viewpoint.  Voyager 2 will be in a better position to view the collision 
from a perspective of looking directly down on the impacts, and it is also
closer at 41 AU.  Jupiter will appear as 2.5 pixels from Voyager 2's
viewpoint and 2.0 pixels for Voyager 1.  If there is any imaging to be
done by Voyager, it will only be by Voyager 2.
 
>  The impacts will occur on the limb of Jupiter as seen from the Galileo
>Space Probe.  However, due to antenna troubles the data transfer rate
>back to Earth is slow and as a result the onboard computer will still
>have data from the Ida (asteroid) encounter.  Either some of the Ida
>images will need to be erased or some of the Jupiter/comet observations
>will need to be omitted.
 
The Ida data playback is scheduled to end at the end of June, so there should
be no tape recorder conflicts with observing the comet fragments colliding
with Jupiter.  The problem is how to get the most data played back when Galileo
will only be transmitting at 10 bps.  One solution is to have both Voyager 2
and Galileo record the event and and store the data on their respective
tape recorders.  The Voyager 2 data will be played back first at something
like 3500 bps.  The images will be small, but at least the time of each
comet fragment impact can be determined.  Using this information, data
can be selectively played back from Galileo's tape recorder.  From Galileo's
perspective, Jupiter will be 60 pixels wide and the impacts would only show
up at about 1 pixel, but valuable science data can still collected in the
visible and IR spectrum along with radio wave emissions from the impacts.
 
The imaging of the comet impacts by Voyager and Galileo has not
been officially approved yet, but from what I hear it looks very likely.

     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [email protected]
    | | | |  __ \ /| | | |     Jet Propulsion Lab | 
 ___| | | | |__) |/  | | |__   Galileo S-Band     | "Why must hailstones always
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 |  be the size of something
|_____|/  |_|/       |_____|/                     |  else?"   George Carlin 

Article: 48677
From: [email protected] (Anne Raugh)
Newsgroups: alt.sci.planetary,sci.space,sci.astro
Subject: Shoemaker-Levy/Jupiter Impact Fact Sheet
Date: 15 Dec 1993 17:25:50 GMT
Organization: U. of Maryland @ College Park, Astronomy
 
The following fact sheet was prepared for distribution by the press offices
of the American Astronomical Society and the Division of Planetary Sciences
and other institutions to respond to the many questions being received about
the impending collision.  Printed copies are available from the AAS and DPS 
press offices.
 
		    *************************************
 
Fact Sheet: Comet Shoemaker-Levy 9 and Jupiter
----------------------------------------------
 
     A comet, already split into many pieces, will strike the
planet Jupiter in the third week of July of 1994.  It is an event
of tremendous scientific interest but, unfortunately, one which is
likely to be totally unobservable by the general public.
Nevertheless, it is a unique phenomenon and secondary effects of
the impacts will be sought after by both amateur and professional
astronomers.
 
 
Significance
 
   The impact of comet Shoemaker-Levy 9 onto Jupiter represents
the first time in human history that people have discovered a body
in the sky and been able to predict its impact on a planet more
than seconds in advance.  The impact will deliver more energy to
Jupiter than the largest nuclear warheads ever built, and up to
several percent of the energy delivered by the impact which caused
the extinction of the dinosaurs on Earth, 65 million years ago.
 
  
History
 
   The comet, the ninth short-period comet discovered by Gene and
Carolyn Shoemaker and David Levy, was first seen on a photograph
taken on the night of 18 March 1993 with the 0.4-meter Schmidt
telescope at Mt. Palomar.  On the original image it appeared
'squashed'.  Subsequent photographs at a larger scale taken by Jim
Scotti with the Spacewatch telescope at Kitt Peak showed that the
comet was split into many separate fragments.  Before the end of
March it was realized that the comet had made a very close
approach to Jupiter in mid-1992 and at the beginning of April,
after sufficient observations were made to determine the orbit
more reliably, Brian Marsden found that the comet is in orbit
around Jupiter and by late May it appeared that the comet was
likely to impact Jupiter in 1994.  Since then, the comet has been
the subject of intensive study.  Searches of archival photographs
have identified pre-discovery images of the comet from early March
1993 but searches for even earlier images have been unsuccessful.
 
 
Cometary Orbit
 
   According to the most recent computations, the comet passed a
little more than half a Jovian radius above the clouds of Jupiter
on 8 July 1992.  The individual fragments separated from each
other 1 1/2 hours after closest approach to Jupiter and they are
all in orbit around Jupiter with an orbital period of about two
years.  Calculations of the orbit prior to 8 July 1992 are very
uncertain but it seems very likely that the comet was previously
in orbit around Jupiter for two decades or more.  Because the
orbit takes the comet nearly 1/3 of an astronomical unit (30
million miles) from Jupiter, the sun causes significant changes in
the orbit.  Thus, when the comet again comes close to Jupiter in
1994 it will actually impact the planet, moving almost due
northward at 60 km/sec aimed at a point only halfway from the
center of Jupiter to the visible clouds.  
   The 21 identified fragments will all hit Jupiter in the
southern hemisphere, at latitudes near 45 degrees between 15 and 25 July
1994, approaching the atmosphere at an angle roughly 45 degrees from the
vertical.  The times of the impacts are now known only to the
nearest half day or so but observations in early 1994 will
significantly improve the precision of the predictions.  The
impacts will occur on the back side of Jupiter as seen from Earth
in an area that is also in darkness.  Because Jupiter's rotational
period is a bit less than 10 hours, the point of impact will be
carried by Jupiter's rotation to the front, illuminated side about
two hours after the impact.  The grains ahead of and behind the
comet will impact Jupiter over a period of four months, centered
on the time of the impacts of the major fragments.  The grains in
the tail of the comet will pass behind Jupiter and remain in orbit
around the planet.
 
 
The Nature of the Comet
 
   The exact number of large fragments is not certain since the
best images show hints that some of the larger fragments may be
multiple.  At least 21 major fragments have been identified.  No
observations are capable of resolving the individual fragments to
show the nuclei.  Images with the Hubble Space Telescope suggest
that there are discrete nuclei in each of the largest several
nuclei which, although not spatially resolved, produce a single,
bright pixel that stands out above the surrounding coma of grains. 
Reasonable assumptions about the spatial distribution of the
grains and about the reflectivity of the nuclei imply sizes of 2
to 4 km (diameter) for each of the 11 brightest nuclei.  Because
of the uncertainties in these assumptions, the actual sizes are
very uncertain and there is a small but not negligible possibility
that the peak in the brightness at each fragment is due not to a
nucleus but to a dense cloud of grains.
   No outgassing has been detected from the comet but calculations
of the expected amount of outgassing suggest that more sensitive
observations are needed because most ices vaporize so slowly at
Jupiter's distance from the sun.  The spatial distribution of dust
suggests that the material ahead of and behind the major fragments
in the orbit are likely large particles from the size of sand up
to boulders.  The particles in the tail are very small, not much
larger than the wavelength of light.  The brightnesses of the
major fragments were observed to change by factors up to 1.7
between March and July 1993, although some became brighter while
others became fainter.  This suggests intermittent release of gas
from the nuclei.
   Studies of the dynamics of the breakup suggest that the
structural strength of the parent body was very low and that the
parent body had a diameter of order 5 km.  This is somewhat
smaller than one would expect from putting all the observed
fragments back together but the uncertainties in both estimates
are large enough that there is no inconsistency.  
 
 
The Impact into Jupiter
 
   The predicted outcomes of the impacts with Jupiter span a large
range.  This is due in part to the uncertainty in the size of the
impacting bodies but even for a fixed size there is a wide range
of predictions, largely because planetary scientists have never
observed a collision of this magnitude.  If the cometary nuclei
have the sizes estimated from the observations with the Hubble
Space Telescope and if they have the density of ice, each fragment
will have a kinetic energy equivalent to somewhat less than a
million megatons of TNT.  The predictions of the effects differ in
how they model the physical processes and there are significant
uncertainties in the processes that will dominate the interaction. 
If ablation (melting and vaporization) and fragmentation dominate,
the energy can be dissipated high in the atmosphere with very
little material penetrating far beneath the visible clouds.  If
the shock wave in front of the nucleus also confines the sides and
causes it to behave like a fluid, then the nuclei could penetrate
far below the visible clouds.  Even in this case, there are
disagreements about the depth to which the material will
penetrate, with the largest estimates being several hundred
kilometers below the cloudtops.  
   In any case, there will be an optical flash lasting a few
seconds as each nucleus passes through the stratosphere.  The
brightness of the flash will depend critically on the fraction of
the energy which is released at these altitudes.  If a large
fragment penetrates below the cloudtops and releases much of its
energy at large depths, a buoyant hot plume will rise in the
atmosphere like a nuclear fireball, producing a flash lasting a
minute or more, radiating most strongly in the infrared.  Although
the impacts will occur on the far side of Jupiter, estimates show
that the flashes will be bright enough to be observed from Earth
in reflection off the inner satellites of Jupiter, particularly
Io, if the satellite happens to be on the far side of Jupiter but
still visible as seen from Earth.  The flashes may also be
visible, just on the limb of Jupiter, as seen from the Galileo
spacecraft.  
   The shock waves produced by the impact onto Jupiter are
predicted to penetrate into the interior of Jupiter, where they
will be bent, much as the seismic waves from earthquakes are bent
in passing through the interior of Earth. These may lead to a
prompt (within an hour or so) enhancement of the thermal emission
over a very large circle centered on the impact but extending past
the limb to the front side of Jupiter.  Waves reflected from the
density-discontinuities in the interior of Jupiter might also be
visible on the front side within an hour or two of the impact. 
Finally, the shock waves may initiate natural oscillations of
Jupiter, similar to the ringing of a bell, although the
predictions disagree on whether these oscillations will be strong
enough to observe with the instrumentation currently available. 
Observation of any of these phenomena can provide a unique probe
of the interior structure of Jupiter, for which we now have only
theoretical models with almost no observational data.  
   The plume of material that would be brought up from Jupiter's
troposphere (below the clouds) will bring up much material from
the comet as well as material from the atmosphere itself.  Much of
the material will be dissociated and even ionized but the
composition of this material can give us clues to the chemical
composition of the atmosphere below the clouds.  It is also widely
thought that as the material recombines, some species, notably
water, will condense and form clouds in the stratosphere.  The
spreading of these clouds in latitude and longitude can tell us
about the circulation in the stratosphere and the altitude at
which the clouds form can tell us about the composition of the
material brought up from below.  The grains of the comet which
impact Jupiter over a period of several months may form a thin
haze which will also circulate through the atmosphere.  Enough
clouds might form high in the stratosphere to completely obscure
the clouds at lower altitudes that are normally seen from Earth.
   Interactions of cometary material with Jupiter's magnetic field
have been predicted to lead to observable effects on Jupiter's
radio emission, injection of material into Jupiter's auroral zone,
and disruption of the ring of grains that now encircles Jupiter. 
Somewhat less certainly the material may cause observable changes
in the torus of plasma that circles Jupiter in association with
the orbit of Io or release of gas in the outer magnetosphere of
Jupiter.  It has also been predicted that the cometary material
may, after ten years, form a new ring about Jupiter although there
are some doubts that this can happen.
 
 
Plans to Study the Event
 
   It is generally expected that nearly every observatory in the
world will be observing events associated with the impact.  These
observatories will include several Earth-orbiting telescopes
(Hubble Space Telescope, International Ultraviolet Explorer,
Extreme Ultraviolet Explorer) and several interplanetary
spacecraft (Galileo, Clementine, and possibly others).  Most
observatories are setting aside time and resources but delaying
detailed planning until the last possible minute in order to
optimize their observations based on the latest theoretical
predictions and the latest observations of the cometary
properties.
   In mid-December Jupiter and the comet will be just reappearing
after having been hidden behind the sun for several months. 
Observations of the comet will begin almost immediately after its
reappearance.  Several ground-based telescopes will carry out
programs to study the long-term changes in brightness of the
fragments, the changes in the spatial distribution of the grains,
the spectral properties of the comet to constrain the composition
of the grains, and to estimate better the size of the nuclear
fragments which will be more easily separated from the grains with
the repaired HST.
   Support for the studies of the event will be coming from many
sources.  Within the United States, support is being supplied by
NASA, by NSF, by DoD, and by many observatories which operate
under private or state-university budgets.  Around the world,
studies are being supported by national governments, by
universities, by research societies, and by various international
organizations such as the International Science Foundation, the
European Space Agency, and the European Southern Observatory.
 
 
Further Information
 
People wanting further information about opportunities for the general
public should contact the Planetary Society.  Address inquiries to:
The Planetary Society, 85 North Catalina Ave., Pasadena CA 91106,
telephone (818) 793 5100. Updated information will be published
regularly in the monthly magazine "Sky and Telescope" and the monthly
magazine "Astronomy".  These can be obtained at newsstands or
libraries as well as by subscription.  Accredited press reporters can
contact the Press Officer of the American Astronomical Society (Dr.
Stephen Maran, AAS Executive Office (202) 328 2010) or the Press
Officer of the Division for Planetary Sciences of the AAS (Dr. Nadine
Barlow, Lunar and Planetary Institute (713) 280 9021). 
 
This fact sheet will be updated intermittently, perhaps once per
month, as new developments dictate.  It is distributed through the
American Astronomical Society and other distribution mechanisms. 
 
Michael F. A'Hearn
Lucy-Ann A. McFadden
Department of Astronomy
University of Maryland
13 December 1993
 

Article: 48706
Newsgroups: alt.sci.planetary,sci.space,sci.astro
From: [email protected] (David Tholen)
Subject: Re: Shoemaker-Levy/Jupiter Impact Fact Sheet
Sender: [email protected]
Organization: University of Hawaii
Date: Thu, 16 Dec 1993 11:10:27 GMT
 
Michael Olea writes:
 
> 	I guess there is just no hope that the popular press will
> ever get it straight:  YES, THERE WAS A BIG IMPACT ON EARTH 65
> MILLION YEARS AGO; NO, IT PROBABLY DID NOT "CAUSE" THE EXTINCTION
> OF THE DINOSAURS, WHO WERE BY AND LARGE ALREADY DEAD AT THE TIME
> OF IMPACT.
> 
> 	So, Anne Raugh, please take a little care, when reporting as
> fact, in passing, mostly discredited hypotheses.
 
There's just one problem:  the hypothesis that an impact 65 million
years ago caused the extinction of the dinosaurs has NOT been "mostly
discredited".
 
I suggest you heed your own advice.
 
P.S.  Anne Raugh was merely posting the item, which was written by
      Mike A'Hearn and Lucy McFadden, so you're directing your flame
      to the wrong person.
 
P.P.S.  When did USENET start being known as the "popular press"?

Article: 49280
From: [email protected] (Dan Bruton, Texas A&M)
Newsgroups: sci.astro
Subject: Comet/Jupiter Collision FAQ (impact times)
Date: 28 Dec 1993 19:33 CDT
Organization: Texas A&M University OpenVMScluster
 
(See table under question Q2.1 for the latest predictions for times of impact.)
 
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *                                                                           *
 *                        Comet/Jupiter Collision FAQ                        *
 *                                                                           *
 *     The following is a list of frequently asked questions concerning the  *
 * collision of comet Shoemaker-Levy 9 with Jupiter.  Thanks to all those    *
 * who have contributed.  Contact Dan Bruton ([email protected]) or John Harper *
 * ([email protected]) with comments, additions, corrections, etc.  The       *
 * Postscript version and updates of this FAQ are available via anonymous    *
 * ftp to tamsun.tamu.edu (128.194.15.32) in the /pub/comet directory.       *
 *                                                                           *
 *                         Last updated 28-Dec-1993                          *
 *                                                                           *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 
GENERAL QUESTIONS
 
Q1.1:  Is it true that a comet will collide with Jupiter in July 1994?
Q1.2:  Who are Shoemaker and Levy?
Q1.3:  Where can I find a GIF image of this comet?
Q1.4:  What will be the effect of the collision?
 
SPECIFICS
 
Q2.1:  What are the impact times of each comet fragment?
Q2.2:  What are the orbital parameters of the comet?
Q2.3:  Why did the comet break apart?
Q2.4:  What are the sizes of the fragments and how long is the fragment train?
Q2.5:  How can I observe the collisions?
Q2.6:  Will Hubble, Galileo or Voyager be able to image the collision?
 
GENERAL QUESTIONS 
 
Q1.1:  Is it true that a comet will collide with Jupiter in July 1994?
 
     Yes, the shattered comet Shoemaker-Levy 9 (1993e) is expected to collide 
with Jupiter over a 5.6 day period in July 1994.  The first of 21 comet 
fragments is expected to hit Jupiter on July 16, 1994 and the last on 
July 22, 1994.  All components of the comet will hit on the dark farside 
of Jupiter, out of sight from Earth.  The impact of the center of the comet 
train is predicted to occur at about -44 degrees Jupiter latitude at a point 
about 70 degrees east (toward the sunrise terminator) from the midnight 
meridian.  About 1.5 hours after each hit, the impact points will rotate into 
view as seen from Earth.   
 
Q1.2:  Who are Shoemaker and Levy?
 
     Eugene and Carolyn Shoemaker and David H. Levy found the 13.8 magnitude
comet on March 25, 1993 on photographic plates taken on March 22, 1993.  The 
photographs were taken at Palomar Mountain in Southern California with a 
0.46 meter Schmidt camera and were examined using a stereomicroscope to reveal
the comet [2,14].  James V. Scotti confirmed their discovery with the 
Spacewatch Telescope at Kitt Peak in Arizona.  See [11] for more information 
about the discovery.
 
Q1.3:  Where can I find a GIF image of this comet?
 
    Some GIF images can be obtained via anonymous ftp from pdssbn.astro.umd.edu 
in the /ftp/pub/images directory.  The GIF images here are named SL9*.GIF.
Also there are a some Hubble Space Telescope images at ftp.cicb.fr in the 
/pub/Images/ASTRO/hst directory.  The GIF images here are named 1993e*.GIF.  
(Also see references for photos.)
 
Q1.4:  What will be the effect of the collision? 
 
     Kevin Zahnle from JPL predicts that each comet fragment will explode into
a fireball about 200 km below the cloudtops of Jupiter.  The fireball will 
initially be hidden underneath the cloudtops but will expand rapidly, with the 
plume material rising to about 1.02 to 1.25 Jupiter radii above the cloudtops.
The temperature of the fireball may reach up to 30,000 degrees C with a 
luminosity of 4x to 25x the brightness of Jupiter.  
     The energy of collision is said to be equivalent to between 200,000 and 
100,000,000 megatons of TNT.   The lower number is for 1 km diameter fragments;
current nuclei diameter estimates range from 1/2 km to as high as 3 or 4 km.  
The fragments will be traveling with a speed of 60 km/sec relative to Jupiter 
[9].  The explosions could cause ammonia ice to well up to the top layers of 
Jupiter's atmosphere forming high cirrus clouds that would create an 
abnormally bright equatorial cloud zone [8].  The clouds may also partially 
obscure atmospheric activity such as the Red Spot much like in the case of
Uranus' atmosphere whose Voyager flyby images revealed a near featureless disk.
     The dust "wings" of the comet will start interacting with the planet more 
than a month ahead of the large fragments, and will continue to interact for 
more than a month afterward.  The long-term monitoring of Jupiter is therefore 
even more important.                                              
     There is a technical paper on the consequences of the explosions available
via anonymous ftp from oddjob.uchicago.edu in the /pub/jupiter directory.  
The paper and figures are available in Postscript format; a couple of the 
computational figures are also available in TIFF format. 
 
 
SPECIFICS
 
Q2.1:  What are the impact times of each comet fragment?
 
	The table below is part of John Spencer's post and shows the estimated 
impact times and the Galilean satellite reflector availability.  See the file 
named Spencer-impact.times in the /pub/predictions/entry directory of 
pdssbn.astro.umd.edu for more information.
 
===============================================================================
     Nucleus        UT date of          
   Designation     impact (July)           Satellite Orbital Longitudes
-----------------  -------------          (degrees past superior conj.) 
Jewitt   Sekanina  Fitted  IAUC     -------------------------------------------
DPS abs  Preprint  Time    5906     Amalthea   Io    Europa  Ganymede  Callisto 
===============================================================================
  21        A 	   16.81              194     340+    103+      75+      35+
  20        B 	   17.08               25*     34+    130       89+      41+
  19        C 	   17.27              168      74+    150       99+      45+
  18        D 	   17.46              304     112     169      108       49+
  17        E 	   17.61   17.6        49+    142     183      115       52+
  16        F 	   17.98              320+    218     221      134       60+
  15        G 	   18.29   18.3       184     281     253      150       67+
  14        H 	   18.79   18.8       183      22+    303+     175       78+
  13        J 	   19.08               37+     83+    333+     190       84+
  12        K 	   19.41   19.4       272     149       6*     206       91+
  11        L 	   19.91   19.9       271     250      57+     231      102+
  10        M 	   20.24              152     318+     90+     248      109+
   9        N 	   20.40              265     350+    106      256      112
   8        P 	   20.61               58+     33+    128      266      117
   7        Q 	   20.82   20.8       207      75+    149      277      121
   6        R 	   21.21   21.3       135     156     189      297+     130
   5        S 	   21.63   21.6        78+    241     231      318+     139
   4        T 	   21.73              150     261     241      323+     141
   3        U 	   21.91              281     298     260      332+     145
   2        V 	   22.19              117     353o    287      345+     151
   1        W 	   22.33   22.3       219      22+    302+     353+     154
------------------------------------------------------------------------------
Uncertainties:     0.1      0.1       72     20       10        5        2
==============================================================================
                              (posted 17 Dec 1993)
 
Key :  "+" means that the impact will be visible from the satellite 
       "*" means the satellite will be visible in eclipse
       "o" means the satellite will be occulted by Jupiter
 
     See the file called nucl_impact.931217 at pdssbn.astro.umd.edu 
/pub/predictions/geometry for impact locations and impact times by 
Sekanina, Chodas, Yeomans, and Scotti.   With continuous astrometry 
starting in January 1994, the following are for 3-sigma (uncertainty) 
predictions for the fragment impact times:  
 
       at minus 2 months  -  55 minutes                            
       at minus 1 month   -  40 minutes                          
       at minus 1 week    -  21 minutes                                 
       at minus 6 hours   -   9 minutes                                
 
The time between impacts is thought to be know with more certainty than the 
actual impact times.  This means that if somehow the impact time of the first 
fragment can be measured experimentally, then impact times of the fragments 
that follow can be predicted with more accuracy.
 
Q2.2:  What are the orbital parameters of the comet?
 
     Shoemaker-Levy 9 is thought to have made its closest approach to Jupiter 
on July 8, 1992 at a distance of about 1.53 Jupiter radii from Jupiter's 
center [8].  The comet is thought to have reached apojove (farthest from 
Jupiter) on July 14, 1993 at a distance of about 0.33 Astronomical Units 
from Jupiter's center.  The orbit looks somewhat elliptical.  See postscript 
files on pdssbn.astro.umd.edu in the /ftp/pub/images directory for a visual 
representation.  The right ascension and declination of the comet along with 
some orbital elements can be obtained via anonymous ftp at pdssbn.astro.umd.edu
in the /pub/ephemeris directory.  The filenames are elements.28, iauc5893 and 
iauc5892.        
 
Q2.3:  Why did the comet break apart?
 
     The comet is thought to have broken apart due to tidal forces on its 
closest approach to Jupiter (perijove) on July 8, 1992.  Shoemaker-Levy 9 is 
not the first observed comet to break apart.  Comet West shattered in 1976 
near the Sun [3].  Astronomers believe that in 1886 Comet Brooks 2 was ripped 
apart by tidal forces near Jupiter [2].  
     Furthermore, images of Callisto and Ganymede show crater chains which may 
have resulted from the impact of a comet similar to Shoemaker-Levy 9 [3].  
The satellite with the best example of aligned craters is Callisto with 13 
crater chains.  There are three crater chains on Ganymede.  These were first 
thought to be from basin ejecta; in other words secondary craters.  There are 
also a few examples on our Moon.  Davy Catena for example, which may have been
due to comets split by Earth.  
 
Q2.4:  What are the sizes of the fragments and how long is the fragment train?
 
     Images taken with the Hubble Space Telescope suggest 3-5 km diameter 
fragments.  Models of Shoemaker-Levy's breakup in 1992 suggest that the 
original intact comet may have been only 2 km across.  If this is the case,
the largest fragments could be no more that 500 meters across [1].
     The angular length of the train was about 51 arcseconds in March 1993 [2].
The length of the train then was about one half the Earth-Moon distance.
In the day just prior to impact, the fragment train will stretch across 20
arcminutes of the sky, more that half the Moon's angular diameter.  The 
translates to a physical length of about 4 million kilometers.  
 
Q2.5:  How can I observe the collisions?  
 
     One can monitor the atmospheric changes on Jupiter using the naked eye,
photography, or CCD imaging.  It is important, however, to observe Jupiter for
several months in advance in order to know which features are due to comet 
impacts and which are naturally occurring.  A video camera may be able to 
record real time atmospheric changes if your telescope is big enough.  The 
Red Spot and other features have been recorded using a video camera and a 
14" telescope with eyepiece projection (2" eyepiece works best).  With WWV 
ticking away in the background one can obtain an excellent record of this 
unusual event.
     One may be able to witness the collisions indirectly by monitoring the 
brightness of the Galilean moons that may be behind Jupiter as seen from 
Earth.  Some suggest that moons may brighten by as much as 0.2 to 2 magnitudes
(ALPO conference, August 1993).  The MSDOS program GALSAT will calculate and 
display the locations of the Galilean satellites for a given day and time and 
can be obtained via ftp from oak.oakland.edu in the /pub/msdos/astronomy 
directory.  One could monitor the moons using a photometer, a CCD, or a video 
camera pointed directly into the eyepiece of a telescope.  If you do video you
can get photometric information by frame grabbing and treating these like CCD 
frames (applying darks, bias', and flats).
     Radio emissions due to the impacts may be strong enough to be detected by 
small radio telescopes.  Some suggest to listen in on 15-30 MHz during the 
comet impact, but to avoid 27 MHz because this frequency is used for CB 
communications (ALPO conference, August 1993).  So it appears that one could 
use the same antenna for both the Jupiter/Io phenomenon and the Jupiter/comet 
impact.  There is an article in Sky & Telescope which explains how to built a 
simple antenna for observing the Jupiter/Io interaction [4].
 
Q2.6:  Will Hubble, Galileo or Voyager be able to image the collision?
 
     The Hubble Space Telescope, like earthlings, will not be able to see
the collisions but will be able to monitor atmospheric changes on Jupiter.
The comet collisions are visible from both Voyager 1 and Voyager 2.
Voyager 1 will be 52 AU from Jupiter and will have a near-limb observation
viewpoint.  Voyager 2 will be in a better position to view the collision from
a perspective of looking directly down on the impacts, and it is also
closer at 41 AU.  Jupiter will appear as 2.5 pixels from Voyager 2's
viewpoint and 2.0 pixels for Voyager 1.  If there is any imaging to be
done by Voyager, it will only be by Voyager 2.
     The impacts will occur on the limb of Jupiter as seen from the Galileo
Space Probe.  The Ida data playback is scheduled to end at the end of June, so
there should be no tape recorder conflicts with observing the comet fragments 
colliding with Jupiter.  The problem is how to get the most data played back 
when Galileo will only be transmitting at 10 bps.  One solution is to have 
both Voyager 2 and Galileo record the event and and store the data on their 
respective tape recorders.  The Voyager 2 data will be played back first at 
something like 3500 bps.  The images will be small, but at least the time of 
each comet fragment impact can be determined.  Using this information, data
can be selectively played back from Galileo's tape recorder.  From Galileo's
perspective, Jupiter will be 60 pixels wide and the impacts would only show
up at about 1 pixel, but valuable science data can still collected in the
visible and IR spectrum along with radio wave emissions from the impacts.  
The imaging of the comet impacts by Voyager 2 and Galileo has not been 
officially approved yet, but it is very likely to happen.
 
 
REFERENCES
 
 [1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
 [2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993, 
      page 38-39.
 [3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
      chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
 [4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
 [5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
 [6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
 [7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
 [8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy, 
      September 1993, page 18.
 [9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
 [10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
 [11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
 [12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision 
      of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
 [13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet 
      Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
 [14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
      January 1994, page 40-44.
 [15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
 
ACKNOWLEDGMENTS
 
     Thanks to Ross Smith for starting a FAQ and to all those who have 
contributed :  Mordecai-Mark Mac Low, Phil Stooke, Rik Hill, Robb Linenschmidt
Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke, David H. Levy,
Richard A. Schumacher, Louis A. D'Amario, John McDonald, Michael Moroney, 
Byron Han, Wayne Hayes, and David Tholen.
 
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .  
|| Texas A & M    ||                `.           .             
|| [email protected] ||               `.              ` : :        ` 
||||||||||||||||||||                                              .  
                                                                     .
 

Article: 2952
From: [email protected] (Dan Bruton, Texas A&M)
Newsgroups: alt.sci.planetary
Subject: Comet/Jupiter Collision
Date: 6 Jan 1994 04:11 CDT
Organization: Texas A&M University OpenVMScluster
 
  ======================================================================  
  ADDENDUM
  --------
 
      A quick note to alert everyone to an important change in the SL9
  impact predictions.  As previously noted, the new impact times are a
  day or so earlier than previously thought, with the first nucleus
  hitting Jupiter around July 16.8.
 
      Even more interesting, the impact point has changed as well as the
  impact times.  IAU Circular 5909, issued on December 17th, reports
  than calculations by Yeomans and Chodas, based on the new astrometry,
  give the impacts occurring ONLY 5-10 DEGREES BEHIND JUPITER'S MORNING
  LIMB, at 47 - 49 degrees S latitude.  This is great news for studying
  the after-effects of the impacts:  The impact sites will be visible
  only 12 - 24 minutes after impact rather than the couple of hours
  previously supposed.  And anything ejected higher than 500-1000 km
  above the cloud tops during the impacts will be directly visible from
  Earth!  Galileo will get a direct view of the impacts rather than
  the grazing limb view previously expected.
 
      The only bad part about this new prediction is that reflections
  off the satellites will not be visible for orbital longitudes
  in the 300-350 degree range, before Jupiter occultation.  But this
  will be amply compensated by the chance to see the flashes reflected
  in any coma still attached to each nucleus by the time it has
  traversed the magnetosphere, or the chance for direct observations
  of impact debris.
 
      Note, by the way, that the nuclei will hit behind the dark limb
  of Jupiter:  The phase angle is 10.6 degrees so the impact sites will
  have to rotate an additional 10 degrees after coming into view
  from Earth before they come into sunlight.
 
  John Spencer
  1993/12/18.
  --------------
  posted 20 Dec 1993, acr
 
  ===========================================================================
 
The file above is part of Spencer-impact.times from the 
/pub/predictions/entry directory of pdssbn.astro.umd.edu.
 
                                                          .  '
||||||||||||||||||||                                            .
|| Danny Bruton   ||                  .         .             .  
|| Texas A & M    ||                `.           .             
|| [email protected] ||               `.              ` : :        ` 
||||||||||||||||||||                                              .  
                                                                     .

In the last day or 2, there has been info on the net to the effect that there is
no funding for the Voyager 2 part of the observation scheme (Gal and V2 watch
the collision, play back V2 at 3.5Kbps, find exact time of collision,
selectively play back Gal at 10bps.)

Sigh.

Burns

Article: 50694
From: [email protected] (Dan Bruton, Texas A&M)
Newsgroups: sci.astro
Subject: Comet/Jupiter Collision FAQ (new impact times)
Date: 19 Jan 1994 00:09 CDT
Organization: Texas A&M University OpenVMScluster
 
Changes from last Posting:
 
    The latest predictions of times and locations of fragment impacts are 
given below.  Answers to all questions except Q1.2 and Q1.3 have been updated.
 
To subscribe to the "Comet/Jupiter Collision FAQ" mailing list, send a message 
to [email protected].
 
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *                                                                           *
 *                        Comet/Jupiter Collision FAQ                        *
 *                                                                           *
 *                         Last Updated 18-Jan-1993                          *
 *                                                                           *
 *     The following is a list of frequently asked questions concerning the  *
 * collision of comet Shoemaker-Levy 9 with Jupiter.  Thanks to all those    *
 * who have contributed.  Contact Dan Bruton ([email protected]) or John Harper *
 * ([email protected]) with comments, additions, corrections, etc.  The       *
 * Postscript version and updates of this FAQ are available via anonymous    *
 * ftp to tamsun.tamu.edu (128.194.15.32) in the /pub/comet directory or to  *
 * seds.lpl.arizona.edu in the /pub/astro/SL9 directory.  This FAQ is also   *
 * available in hypertext format:                                            *
 *       http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html        *
 *                                                                           *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 
GENERAL QUESTIONS
 
Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
Q1.2: Who are Shoemaker and Levy?
Q1.3: Where can I find a GIF image of this comet?
Q1.4: What will be the effect of the collision?
 
SPECIFICS
 
Q2.1: What are the impact times and impact locations of the comet fragments?
Q2.2: What are the orbital parameters of the comet?
Q2.3: Why did the comet break apart?
Q2.4: What are the sizes of the fragments and how long is the fragment train?
Q2.5: Will Hubble, Galileo, Ulysses, or Voyager be able to image the collisions?
Q2.6: How can I observe the collisions?
Q2.7: To whom do I report my observations?
 
GENERAL QUESTIONS
 
Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 
     Yes, the shattered comet Shoemaker-Levy 9 (1993e) is expected to collide
with Jupiter over a 5.6 day period in July 1994.  The first of 21 comet
fragments is expected to hit Jupiter on July 16, 1994 and the last on
July 22, 1994.  All components of the comet will hit on the dark farside
of Jupiter, out of sight from Earth.  The impact of the center of the comet
train is predicted to occur at about -44 degrees Jupiter latitude at a point
about 67 degrees east (toward the sunrise terminator) from the midnight
meridian.                                                 
     These new impact point estimates from Sekanina, Chodas, and Yeomans 
are much closer to the morning terminator of Jupiter than the old estimates.  
Although they are still all on the far side as viewed from the Earth, they are
now only 5-9 degrees behind the limb.  About 12 - 24 minutes after each hit, 
the impact points will rotate into view as seen from Earth.  For the impact 
locations mentioned above, anything ejected higher than 500-1000 km above the 
cloud tops during the impacts will be visible from Earth.
 
Q1.2: Who are Shoemaker and Levy?
 
     Eugene and Carolyn Shoemaker and David H. Levy found the 13.8 magnitude
comet on March 25, 1993 on photographic plates taken on March 22, 1993.  The
photographs were taken at Palomar Mountain in Southern California with a
0.46 meter Schmidt camera and were examined using a stereomicroscope to
reveal the comet [2,14].  James V. Scotti confirmed their discovery with the
Spacewatch Telescope at Kitt Peak in Arizona.  See [11] for more information
about the discovery.
 
Q1.3: Where can I find a GIF image of this comet?
 
    Some GIF images can be obtained via anonymous ftp from tamsun.tamu.edu
in the /pub/comet directory.  The GIF images here are named SL9*.GIF.
Also there are a some Hubble Space Telescope images at ftp.cicb.fr in the
/pub/Images/ASTRO/hst directory.  The GIF images here are named 1993e*.GIF.
Also see references for photos.
 
Q1.4: What will be the effect of the collision?
 
     Each comet fragment will enter the atmosphere at a speed of 130,000 mph 
(60 km/s).  At an altitude of 100 km above the visible cloud decks, 
aerodynamic forces will overwhelm the material strength of the comet, 
beginning to squeeze it and tear it apart.  Five seconds after entry, the 
comet fragment will deposit its kinetic energy of around 10^28 ergs
(equivalent to around 200,000 megatons of TNT) at 100-150 km below the 
cloud layer [19].  Bigger fragments will have more energy and go deeper.   
     The hot (30,000 K) gas resulting from the stopped comet will explode, 
forming a fireball similar to a nuclear explosion, but much larger.  
The visible fireball will only rise 100 km or so above the cloudtops.
Above that height the density will drop so that it will become transparent.
The fireball material will continue to rise, reaching a height of perhaps
1000 km before falling back down to 300 km.  The fireball will spread out 
over the top of the stratosphere to a radius of 2000-3000 km from the point 
of impact (or so the preliminary calculations say).  The top of the resulting 
shock wave will accelerate up out of the Jovian atmosphere in less than two 
minutes, while the fireball will be as bright as the entire sunlit surface of 
Jupiter for around 45 sec [18].  The fireball will be somewhat red, with a 
characteristic temperature of 2000 K - 4000 K (slightly redder than the sun, 
which is 5000 K).  Virtually all of the shocked cometary material will rise 
behind the shock wave, leaving the Jovian atmosphere and then splashing back 
down on top of the stratosphere at an altitude of 300 km above the clouds 
[unpublished simulations by Mac Low & Zahnle].  Not much mass is involved in 
this splash, so it will not be directly observable.  The splash will be 
heavily enriched with cometary volatiles such as water or ammonia, and so may 
contribute to significant high hazes.
	Meanwhile, the downward moving shock wave will heat the local clouds, 
causing them to buoyantly rise up into the stratosphere.  This will allow 
spectroscopists to attempt to directly study cloud material, a unique 
opportunity to confirm theories of the composition of the Jovian clouds.  
Furthermore, the downward moving shock may drive seismic waves (similar to 
those from terrestrial earthquakes) that might be detected over much of the 
planet by infrared telescopes in the first hour or two after each impact.  
The strength of these two effects remains a topic of research.
	Finally, the disturbance of the atmosphere will drive internal
gravity waves ("ripples in a pond") outwards.  Over the days following the
impact, these waves will travel over much of the planet, yielding information
on the structure of the atmosphere if they can be observed (as yet an
open question).
     The "wings" of the comet will interact with the planet before and
after the collision of the major fragments.  The so-called "wings" are 
defined to be the distinct boundary along the lines extending in both 
directions from the line of the major fragments; some call these 'trails'.  
Sekanina, Chodas and Yeomans have shown that the trails consist of larger 
debris, not dust: 5-cm rock-sized material and bigger (boulder-sized and
building-sized).  Dust gets swept back above (north) of the trail-fragment
line due to solar radiation pressure.  The tails emanating from the major
fragments consist of dust being swept in this manner.  Only the small portion
of the eastern debris trail nearest the main fragments will actually impact
Jupiter, according to the model, with impacts starting only a week before
the major impacts.  The western debris trail, on the other hand, will impact
Jupiter over a period of months following the main impacts, with the latter
portion of the trail actually impacting on the front side of Jupiter as viewed
from Earth.  
	The injection of dust from the wings and tail into the Jovian system 
may have several consequences.  First, the dust will absorb many of the 
energetic particles that currently produce radio emissions in the Jovian 
magnetosphere.  The expected decline and recovery of the radio emission may 
occur over as long as several years, and yield information on the nature and 
origin of the energetic particles.  Second, the dust may actually form a 
second faint ring around the planet.
     There are now two technical papers [18,19] on the atmospheric consequences 
of the explosions available via anonymous ftp from oddjob.uchicago.edu in the 
pub/jupiter directory.  The paper and figures are available in UNIX compressed
Postscript format; a couple of the computational figures are also available 
in TIFF format.
 
 
SPECIFICS
 
Q2.1: What are the impact times and impact locations of the comet fragments?
 
     The new solutions below incorporate astrometric data taken after
December 9, when the comet was first seen after it emerged from solar
conjunction.  The new predictions are much more accurate than the old ones
because they are based on measurements over a longer time span.  The new
impact point estimates are much closer to the morning terminator of Jupiter
than the old estimates; although they are still all on the far side as viewed
from the Earth, they are now only 5-9 degrees behind the limb.
     The following table gives the latest impact predictions.  A letter 
designation for the cometary fragments has become standard. The 21 major 
fragments are denoted A through W in order of impact, with letters I and O 
not used. Fragment A is the closest to Jupiter and will impact first; 
fragment W is the farthest and will impact last; fragment Q is the brightest
(and therefore presumably biggest), with G, H, K, L, and S also quite bright.
 
    +====================================================================+
    | Fragment  UT Date/Hour   Jovicentric     Meridian     Angle Behind |
    |            of Impact     Latitude (deg)  Angle (deg)   Limb (deg)  |
    |                 d  hr                                              |
    |====================================================================|
    |    A      July 16  19       -43.3            64            9       |
    |    B      July 17  02       -43.3            65            9       |
    |    C      July 17  06       -43.4            65            8       |
    |    D      July 17  11       -43.4            65            8       |
    |    E      July 17  14       -43.7            63            8       |
    |    F      July 17  23       -43.5            66            8       |
    |    G      July 18  07       -43.8            66            8       |
    |    H      July 18  19       -43.9            66            7       |
    |    J      July 19  01       -43.7            67            7       |
    |    K      July 19  10       -44.0            67            7       |
    |    L      July 19  22       -44.3            69            7       |
    |    M      July 20  05       -43.9            68            6       |
    |    N      July 20  09       -44.0            68            6       |
    |    P      July 20  14       -44.0            68            6       |
    |    Q      July 20  19       -44.3            69            6       |
    |    R      July 21  05       -44.1            69            5       |
    |    S      July 21  15       -44.4            69            5       |
    |    T      July 21  17       -44.1            70            5       |
    |    U      July 21  21       -44.1            70            5       |
    |    V      July 22  04       -44.1            70            5       |
    |    W      July 22  07       -44.2            70            5       |
    +====================================================================+
 
     The impact times have been quoted to the nearest hour, and do not include
the light time to the Earth (about 40 min); the uncertainty in these times is
about 2 hr.  The impact latitudes are all around -44 deg, well south of the
Great Red Spot.  The meridian angle is the Jovicentric longitude of impact
measured from the midnight meridian (the line of longitude pointed away from
the Sun) to the morning terminator.  The impact points are thus 20-25 deg to
the nightside of the morning terminator. The longitudes of the impacts are
not well known yet because the times are uncertain and Jupiter rotates
quickly; we can only say that the impact points will be scattered around the
planet at the -44 deg latitude line.  The rightmost column gives the angular
distance of the impact point behind Jupiter's limb as seen from the Earth.
The later impacts will be closest to the limb.  These predictions indicate
that the impact of the largest fragment Q will be visible during evening in
Europe and Asia, but will occur in daylight hours for North America.
     See the Postscript file impact.ps at tamsun.tamu.edu in the /pub/comet
directory for a graph with impact times and Galilean moon eclipses.   The 
following are the 3-sigma (uncertainty) predictions for the fragment impact 
times:
          on March 1         -  90 min
          on May 1           -  71 min
          on June 1          -  49 min
          on July 1          -  30 min
          on July 15         -  19 min
          at impact - 18 hr  -  10 min
 
The time between impacts is thought to be known with more certainty than the
actual impact times.  This means that if somehow the impact time of the first
fragment can be measured experimentally, then impact times of the fragments
that follow can be predicted with more accuracy.
 
Q2.2: What are the orbital parameters of the comet?
 
   Comet Shoemaker-Levy 9 is actually orbiting Jupiter, which is most 
unusual: comets usually just orbit the Sun.  Only two comets have ever 
been known to orbit a planet (Jupiter in both cases), and this was inferred 
in both cases by extrapolating their motion backwards to a time before they 
were discovered.  S-L 9 is the first comet observed while orbiting a planet.
Shoemaker-Levy 9's previous closest approach to Jupiter (when it broke up) 
was on July 7, 1992 according to the new solution; the distance from the 
center of Jupiter was about 96,000 km, or about 1.3 Jupiter radii.  The comet 
is thought to have reached apojove (farthest from Jupiter) on July 14, 1993 
at a distance of about 0.33 Astronomical Units from Jupiter's center.  The 
orbit is very elliptical, with an eccentricity of over 0.995.  Computations 
by Paul Chodas, Zdenek Sekanina, Don Yeomans, suggest that the comet has been 
orbiting Jupiter for 20 years or more, but these backward extrapolations of 
motion are highly uncertain.  
     See [14] for a visual representation of the orbit.  The right ascension 
and declination of the comet along with some orbital elements can be obtained 
via ftp at tamsun.tamu.edu in the /pub/comet directory as elements.nuc.
 
Q2.3: Why did the comet break apart?
 
     The comet is thought to have broken apart due to tidal forces on its
closest approach to Jupiter (perijove) on July 7, 1992.  Shoemaker-Levy 9 is
not the first comet observed to break apart.  Comet West shattered in 1976
near the Sun [3].  Astronomers believe that in 1886 Comet Brooks 2 was ripped
apart by tidal forces near Jupiter [2].
     Furthermore, images of Callisto and Ganymede show crater chains which may
have resulted from the impact of a comet similar to Shoemaker-Levy 9 [3,17].
The satellite with the best example of aligned craters is Callisto with 13
crater chains.  There are three crater chains on Ganymede.  These were first
thought to be from basin ejecta; in other words secondary craters.  There are
also a few examples on our Moon.  Davy Catena for example, which may have been
due to comets split by Earth.
 
Q2.4: What are the sizes of the fragments and how long is the fragment train?
 
     Using measurements of the length of the train of fragments and a model 
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the 
parent nucleus of the comet (before breakup) was only about 2 km across [13].
This would imply that the individual fragments are no larger than about 500 
meters across.  However, images of the comet taken with the Hubble Space 
Telescope in July 1993 indicate that the fragments are 3-4 km in diameter 
(based on their brightness).  A more elaborate tidal disruption model by 
Sekanina, Chodas and Yeomans [20] predicts that the original comet nucleus 
was at least 10 km in diameter.  This means the largest fragments could be 
3-4 km across, a size consistent with estimates derived from the Hubble Space
Telescope's observations.                                       
     The angular length of the train was about 51 arcseconds in March 1993 [2].
The length of the train then was about one half the Earth-Moon distance.
In the day just prior to impact, the fragment train will stretch across 20
arcminutes of the sky, more that half the Moon's angular diameter.  This
translates to a physical length of about 5 million kilometers.  The train 
expands in length due to differential orbital motion between the first and 
last fragments.  Here is a table with data on train length based on Sekanina, 
Chodas, and Yeomans's tidal disruption model:
 
           +=============================================+
           |    Date    Angular Length  Physical Length  |
           |               (arcsec)          (km)        |
           +=============================================+
           |  93 Mar 25       49            158,000      |
           |     Jul  1       67            265,000      |
           |  94 Jan  1      131            584,000      |
           |     Feb  1      161            669,000      |
           |     Mar  1      200            762,000      |
           |     Apr  1      255            893,000      |
           |     May  1      319          1,070,000      |
           |     Jun  1      400          1,366,000      |
           |     Jul  1      563          2,059,000      |
           |     Jul 15      944          3,593,000      |
           |    Impact A    1286          4,907,000      |
           +=============================================+
 
Q2.5: Will Hubble, Galileo, Ulysses, or Voyager be able to image the collisions?
 
     The Hubble Space Telescope, like earthlings, will not be able to see the 
collisions but will be able to monitor atmospheric changes on Jupiter. The new
impact points are more favorable for viewing from spacecraft: it can now be
stated with certainty that the impacts will all be visible to Galileo, and now
at least some impacts will be visible to Ulysses.  Although Ulysses does not 
have a camera, it will monitor the impacts at radio wavelengths.  The impact
points are also viewable by both Voyager spacecraft, especially Voyager 2.  
However, it is doubtful that the Voyagers will image the impacts because the 
onboard software that controls the cameras has been deleted, and there is 
insufficient time to restore and test the camera software.  The only Voyager 
instruments likely to observe the impacts are the ultraviolet spectrometer 
and planetary radio astronomy instrument.  Voyager 1 will be 52 AU from 
Jupiter and will have a near-limb observation viewpoint.  Voyager 2 will be in
a better position to view the collision from a perspective of looking directly
down on the impacts, and it is also closer at 41 AU.  
        Galileo will get a direct view of the impacts rather than the grazing
limb view previously expected.  The Ida image data playback is scheduled to 
end at the end of June, so there should be no tape recorder conflicts with 
observing the comet fragments colliding with Jupiter.  The problem is how to 
get the most data played back when Galileo will only be transmitting at 10 bps.
One solution is to have both Ulysses and Galileo record the event and and store
the data on their respective tape recorders.  Ulysses observations of radio 
emissions data will be played back first and will at least give the time of 
each comet fragment impact.  Using this information, data can be selectively 
played back from Galileo's tape recorder.  From Galileo's perspective, Jupiter
will be 60 pixels wide and the impacts will only show up at about 1 pixel, 
but valuable science data can still collected in the visible and IR spectrum 
along with radio wave emissions from the impacts.
 
Q2.6: How can I observe the collisions?
 
     One might be able to detect atmospheric changes on Jupiter using 
photography, or CCD imaging.  It is important, however, to observe Jupiter 
for several months in advance in order to know which features are due to comet
impacts and which are naturally occurring.  It appears more and more likely 
that most effects will be quite subtle.  Without a large ( > 15" ?) telescope 
and good detector, little is likely to be seen.  
     One may be able to witness the collisions indirectly by monitoring the
brightness of the Galilean moons that may be behind Jupiter as seen from
Earth.  However, current calculations suggest that the brightenings may
be as little as 0.05% of the sunlit brightness of the moon [18].  If Io can 
be caught in eclipse but visible from the earth during an impact, prospects 
will improve significantly.  The MSDOS program GALSAT will calculate and 
display the locations of the Galilean satellites for a given day and time 
and can be obtained via ftp from oak.oakland.edu in the /pub/msdos/astrnomy 
directory.  One could monitor the moons using a photometer, a CCD, or a video 
camera pointed directly into the eyepiece of a telescope.  If you do video you
can get photometric information by frame grabbing and treating these like CCD 
frames (applying darks, biases, and flats).
     The cutoff of radio emissions due to the entry of cometary dust into the 
Jovian magnetosphere during the weeks around impact may be clear enough to be 
detected by small radio telescopes.  Furthermore, impacts may be directly 
detectable in radio frequencies.  Some suggest to listen in on 15-30 MHz during
the comet impact, but to avoid 27 MHz because this frequency is used for CB 
communications (ALPO conference, August 1993).  So it appears that one could 
use the same antenna for both the Jupiter/Io phenomenon and the Jupiter/comet 
impact.  There is an article in Sky & Telescope magazine which explains how to
build a simple antenna for observing the Jupiter/Io interaction [4].
 
Q2.7: To whom do I report my observations?
 
   Observation forms by Steve Lucas are available via ftp at tamsun.tamu.edu
in the /pub/comet directory.  These forms also contain addresses of "Jupiter 
Watch Program" section leaders.   JUPCOM.ZIP contains Microsoft Write files.
For other addresses see page 44 of the January 1994 issue of Sky & Telescope
magazine [14].
 
 
REFERENCES
 
 [1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
 [2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
       page 38-39.
 [3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
       chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
 [4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
 [5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
 [6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
 [7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
 [8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
       September 1993, page 18.
 [9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
 [10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
 [11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
 [12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
       of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
 [13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
       Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
 [14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
       January 1994, page 40-44.
 [15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
 [16] "AstroNews", Astronomy, January 1994, page 19.
 [17] "AstroNews", Astronomy, February 1994, page 16.
 [18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
       Comet Shoemaker Levy 9", submitted to Icarus October 29,1993.
 [19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
       Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
       submitted to Nature January 7,1994.
 [20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the 
       Appearance of Periodic Comet Shoemaker-Levy 9", submitted to Astronomical
       Journal, November 1993.
 
 
ACKNOWLEDGMENTS
 
     Thanks to Ross Smith for starting a FAQ and to all those who have
contributed :  Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke, Rik Hill,
Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke, David H. Levy,
Eugene and Carolyn Shoemaker, Jim Scotti, Richard A. Schumacher, 
Louis A. D'Amario, John McDonald, Michael Moroney, Byron Han, Wayne Hayes, 
David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki, Jeffrey A Foust, 
Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina, Don Yeomans, and
Richard Schmude.
 
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 
 
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .  
|| Texas A & M    ||                `.           .             
|| [email protected] ||               `.              ` : :        ` 
||||||||||||||||||||                                              .  
                                                                     .

Article: 3689
From: [email protected] (MARK LANGFORD)
Newsgroups: clari.tw.space,clari.local.texas
Subject: Scientists gear up for summer collision between Jupiter, errant comet
Date: Tue, 25 Jan 94 12:51:41 PST
 
	AUSTIN, Texas (UPI) -- Earth-bound observatories will be trained on
Jupiter this summer for what scientists are calling an unprecedented
opportunity to study a titanic collision between the giant gas planet
and an errant comet.

	Although the comet is expected to slam into Jupiter's backside -- out
of view of Earth-based telescopes -- scientists will watch for flashes of
light reflected from the largest Jovian moons and monitor any changes in
Jupiter's roiling atmosphere.

	``This is like a very large bomb being dropped into Jupiter's
atmosphere,'' said Anita Cochran, a University of Texas research
scientist whose specialty is comets. ``It's much larger than any bomb on
Earth.''

	Based on estimates of the comet's mass, she said the energy expended
in the collision could equal a magnitude 11 or 11.5 earthquake.

	The errant comet is Shoemaker-Levy 9, which approached so close to
Jupiter in July 1992 that it was torn apart, probably by gravitational
forces. Jupiter, which is made of gas, is the solar system's largest planet.

	Scientists predict that between July 16 and July 22, successive
pieces of the comet will slam into Jupiter at speeds of 37 miles (or 60
kilometers) per second.

	Cochran said Shoemaker-Levy was about 6.2 miles (10 kilometers) wide
before it broke apart, and that ``there are 21 major pieces we can see,''
with the largest being almost two miles across.

	``It's pretty rare that we see a comet split up like this,'' she
said. ``We don't fully understand why they break up. It could have had
some really weak areas, and the tidal forces caused it to split.''

	Scientists are not sure what will happen when the collision occurs.
If a large enough piece makes it through Jupiter's outer atmosphere, the
explosion could throw up material from the lower atmosphere, giving
scientists a first-time glimpse of what lies below the planet's cloud-
shrouded surface.

	Within an hour of the impact, Cochran said the impact area will
rotate into Earth's view, and observatories across the country will be
watching for changes in the structure of Jupiter's clouds.

	``It's possible that for a short while the planet will appear quite
dramatically different,'' said Jeff Kanipe, a spokesman for UT's McDonald 
Observatory, which will be watching with all four of its telescopes.

	The McDonald Observatory, nestled in the Davis Mountains of far West
Texas, will train its 107-inch, 82-inch, 36-inch and 30-inch telescopes
on the event. Although the impact will be on Jupiter's far side, there
could be plenty of indirect action to watch.

	``When the pieces hit, depending on how big they are and how deep
they will go into the inner atmosphere, there may be a fire ball that
comes out of Jupiter,'' Cochran said. ``There may be an increase in
light off the other moons.''

	In addition to moon brightness, scientists will look at spectral
lines to determine if any material from the lower atmosphere is dredged
up closer to the surface.

	``We'll be looking at the chemistry in the upper atmosphere,'' Kanipe
said. ``The blast might throw up material from the lower cloud decks.
Some astronomers predict an explosion in the upper cloud deck, but the
dispersal may be very high.''

	Cochran said scientists ``got real unlucky'' when it was determined
there would not be a direct view of the impact. On the other hand, she
said, if the collision was delayed by one month, scientists would see
nothing at all because the sun would obstruct the entire event.

	Jupiter will be 375 million to 400 million miles (603 million to 644
million kilometers) away from Earth when the impact occurs.

	Although the Galileo satellite will be in position to monitor the
collision directly, Cochran said its high-gain antenna is out of service
and it may collect little useful information.

	``It may take images that don't really count,'' she said.

	Kanipe said it is ``unprecedented'' for the McDonald Observatory to
dedicate all four of its telescopes to a single event -- one that ``has
never been observed before.''

	The Kitt Peak observatory in Arizona will also be conducting a
comprehensive study, along with the orbiting Hubble Space Telescope.

	``This is unique because we know it's coming,'' said Cochran. ``It's
the first time we've been able to witness an event like this. It should
tell us a lot about the energy and the effects of such an impact.''

Article: 51825
Newsgroups: sci.astro
From: [email protected] (Richard Stueven)
Subject: Way Cool Big Fun With Shoemaker-Levy
Sender: [email protected] (News Manager)
Organization: Wind River Systems, Inc.
Date: Wed, 2 Feb 1994 18:48:54 GMT
 
Lifted from the 1/31/94 San Francisco Chronicle's "Back Page" [humor, not
science, in case you're wondering]... 
 
Way Cool Big Fun With Shoemaker-Levy
by Jon Carroll
 
The bad news is that a comet is going to hit a very important planet in
our own solar system very soon now.  The good news is, it's not our
planet.  Life will go on much as before, and you will die whenever you
are going to die, without heavenly intervention.
 
What a relief!
 
I am not making this up.  The comet is called Shoemaker-Levy.  It was
originally just the Shoemaker comet, but then it married the Levy
nebula, and so they became the Shoemaker-Levy comet and the
Shoemaker-Levy nebula to indicate that a comet is not automatically
required to take a nebula's name just because a nebula is 1 billion
times bigger and much more important in the universal scheme of things
than a comet, which is just a dirty snowball.
 
One can only hope that the rumors of an unwise liaison with the Crab
nebula are untrue.  There would not be enough Kwell in the whole
universe to handle that particular problem.
 
OK, I made some of that up, but I do wish to emphasize that there
really is a comet called Shoemaker-Levy and it really will crash into
the southern hemisphere of Jupiter sometime in July and produce an
explosion similar in size and power to the one that took out all the
dinosaurs on Earth a while back.
 
Alas, the comet is going to crash into the back side of Jupiter, the
night side, the side away from the Sun and the Earth and responsible
scientists.  This is very sad.  If you don't get to see the coolest
explosion in the whole solar system in this century, what's the point
of being a responsible scientist?
 
But there's hope.  The astronomers may not be able to see the explosion
itself, but they'll be able to see the light from the explosion
reflected off the moons of Jupiter, and that should be pretty cool.
 
And, of course, very useful.  Responsible scientists have a hard time
admitting that they just want to watch things blow up because it's
aesthetically pleasing, so they usually decide to measure the event and
then quantify it and compare it to other known events.
 
That's why it's science and not voyeurism.
 
The atmosphere in a lot of labs resembles the atmosphere in a lot of
Cub Scout meeting rooms.  Yes, there's the fine intellectual challenge
of figuring out the something or other that might explain the origins
of the univers (billions and billions; as Carl Sagan demonstrated,
that's just a lot of fun to say), but also there's sitting around
eating corn chips and raisin-flecked muffins and thinking about an
explosion big enough to wipe out Europe.
 
Sometimes, if you listen to an astronomer muttering under his breath,
you can hear him say, "Wheeeeeeeeeeeeeeeeeeeeeeee BOOM!"
 
And when the big day comes, when Shoemaker-Levy actually smashes into
Jupiter and the radiance of the impact hits the moons of Jupiter and
then the telescopes staffed by responsible scientists, you know what
they'll do?  They'll applaud.
 
Good show, God!
 
They understand that God is a Cub Scout too.  There is nothing cooler
than the Universe.  Exploding stars!  Expanding galaxies!  Continual
thermonuclear explosions at the heart of every star!  The almost total
vacuum of space!
 
You know what happens to a human body when it's suddenly put into an
almost total vacuum?  I'm not going to describe it here, but it's very
cool.
 
So when you get something with the sheer cosmic swagger of
Shoemaker-Levy, the Death Comet, then the juices really start flowing.
If only we could prove that there was something that swallowed solid
hydrogen for breakfast living at the very center of Jupiter, something
that was imperiled by the onrushing inevitability of Shoemaker-Levy,
then that would be just the neatest, greatest, uh, saddest, most
distressing thing ever.
 
Go nuts, big guy!  We'll be there, grinning like crazy, grinning and of
course measuring.
 
---
Richard Stueven        [email protected]         attmail!gakhaus!gak     209/15/19&20
 
 "Hockey isn't a life or death thing.  It's far more important than that."
 
                                       - Kevin Constantine         
 
 "Life is a grapefruit." - Douglas Adams

From:	US1RMC::"[email protected]" "Evan Marshall Manning"  6-FEB-1994 
To:	[email protected]
CC:	
Subj:	Shoemaker-Levy collision with Jupiter predictions

[This is summary of an article that appeared in the Fall 1993 issue of
_Engineering_&_Science_, Caltech's alumni magazine.  The whole article
is 12 pages including photos & figures, so I don't begin to do it
justice here.  If you're really interested you can contact the Caltech
alumni association at (818) 395-3630 about a reprint.  Be warned, the
real article plays up Caltech connections to an annoying extent.] 

On July 8, 1992 Shoemake-Levy passed within 1.6 Jupiter radii (113,000
kilometers) of the center of Jupiter and was torn apart.  There are at
least 21 identifiable fragments, arranged in a straight line.

Its orbit passes within 37,000 kilometers of Jupiter's center, but
Jupiter's radius is 71,400 kilometers.  The fragments will impact over
the period of about five days.  Impacts will be 10 degrees beyond
Jupiter's limb as seen from Earth.  The points on the surface where
impacts occur will rotate into view from Earth about two hours after
they hit. 

At the time of the impacts, Galileo will be only 230 million kilometers
away, and the impacts will be approximately on the limb as seen from
Galileo.

[I just read in _Science_News_ that recent data moves the impacts
closer to the limb.  Good news for Galileo but bad news for seeing
reflections off moons.]

Computer simulations at Caltech show fragments lasting about 10 seconds
and reaching about 350 kilometers below the 1-bar level.  The crash
will create a lot of heat and a flash of white light, brightest when
seen along the comet's path, possibly bright enough that reflections
off nearby moons may be visible from Earth.  Next there should be an
explosion like a 100,000,000 megaton nuclear bomb, creating a huge
plume.  This plume will initially be as bright as the rest of Jupiter
and should be visible from Galileo.  Since the plume should have a
much higher temperature than Jupiter, it will be distinguishable even
when it cannot be resolved.  It could still be about 10 degrees hotter
when it rotates into our view from Earth.

Water from the comet plus water (and maybe other substances) from inside 
Jupiter could make a large white spot or band, observable from Earth.

There may also be ripples through the atmosphere, which may have
large enough peak-to-trough temperature differences to be detected
from Earth in the IR.

Jupiter's spin should form up to ~20 vortices of perhaps 1,000 km
diameter from gas displaced by the impact explosions.  These could be
resolved by Hubble but not by ground-based telescopes.  And the
vortices may merge.

Who's watching:

 - Hubble's WFPC2.
 - A network of ground-based infrared astronomers.
 - Mt. Palomar will give it 11 or 12 evenings in the 1-5 and 10-20 
   micron bands.
 - Owen's Valley will watch in  the microwave region.
 - The Very Large Array (VLA) will watch at 6 centimeters.
 - Galileo
   - radio
   - has only camera with a direct (but edge-on) view.
   - cannot resolve initial explosion but may resolve lightning,
     flashes, and plume.
   - can't send all pictures home.
   - Near-Infrared Mapping Spectrometer (NIMS) and Photopolarimeter
     radiometer (PPR) will get time sequences and tell which camera
     frames to download.
 - Ulysses
   - radio
 - Voyagers 1 & 2
   - radio
   - Voyager 2 has best viewing angle but camera is off for good
   - will use UV spectrometer.

-- 
<<<<<<<<<< Evan M. Manning ======= [email protected] >>>>>>>>>>>>
Your eyes are weary from staring at the CRT.  You feel sleepy.  Notice how
restful it is to watch the cursor blink.  Close your eyes.  The opinions
stated above are yours.  You cannot imagine why you ever felt otherwise.
i=3;do{putchar(((0x18|1<<!(i&2)|(!!i==i)*2)<<2|2>>i%2)^(2<<1+i));}while(i--);

From:	US1RMC::"[email protected]" "JPL Public Information"  
        9-FEB-1994 19:29:31.51
To:	[email protected]
CC:	
Subj:	JPL/Comet-Jupiter rendering GIFs available

GIF files showing depictions of the Comet Shoemaker-Levy 9 impact
with Jupiter in July 1994 are available at the JPL Info public
access computer site.

The files, in the directory `news', are:

SL9REND.GIF      54K    Rendering 3 views of comet-Jupiter collision 2/9/94
SL9REND1.GIF    116K    Larger rendering comet-Jupiter from Earth 2/9/94
SL9REND2.GIF    106K    Larger rendering comet-Jupiter from Voyager 2 2/9/94
SLREND3.GIF     128K    Larger rendering comet-Jupiter from south pole 2/9/94

The renderings were created by David Seal of JPL based on data
from Drs. Donald Yeomans and Paul Chodas.

The JPL Info site may be accessed by Internet anonymous ftp to
jplinfo.jpl.nasa.gov (137.78.104.2), or by dialup modem to 
+1 (818) 354-1333.

[end]

re .21 (signature)
    
i=3;do{putchar(((0x18|1<<!(i&2)|(!!i==i)*2)<<2|2>>i%2)^(2<<1+i));}while(i--);
    
    It prints "Evan".

From:	US1RMC::"WDB3926%[email protected]" 14-FEB-1994 
CC:	
Subj:	Comet/Jupiter Collision FAQ

   This is the latest version of the Comet/Jupiter Collision FAQ.  If
anyone on this mailing list is interested in the creation of a
discussion newsgroup called "alt.current-events.comet.jupiter", then
please followup to a proposal message on the newsgroup alt.config or
send a message to [email protected]. 

Thanks,

Dan

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Recent Changes to this FAQ:

   Question 1.1: Limb and terminator crossings
   Question 1.3: New GIF's available (renditions)
   Question 2.1: Impact times
   Question 2.7: New program and new version of GALSAT
   Question 2.8: Addresses

 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *                                                                           *
 *                        Comet/Jupiter Collision FAQ                        *
 *                                                                           *
 *                         Last Updated 14-Feb-1993                          *
 *                                                                           *
 *     The following is a list of frequently asked questions concerning the  *
 * collision of comet Shoemaker-Levy 9 with Jupiter.  Thanks to all those    *
 * who have contributed.  Contact Dan Bruton ([email protected]) or John Harper *
 * ([email protected]) with comments, additions, corrections, etc.  The       *
 * Postscript version and updates of this FAQ are available via anonymous    *
 * ftp to tamsun.tamu.edu (128.194.15.32) in the /pub/comet directory or to  *
 * seds.lpl.arizona.edu in the /pub/astro/SL9 directory.  This FAQ is also   *
 * available in hypertext format:                                            *
 *       http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html        *
 *                                                                           *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

GENERAL QUESTIONS

 Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 Q1.2: Who are Shoemaker and Levy?
 Q1.3: Where can I find a GIF image of this comet?
 Q1.4: What will be the effect of the collision?

SPECIFICS

 Q2.1: What are the impact times and impact locations of the comet fragments?
 Q2.2: What are the orbital parameters of the comet?
 Q2.3: Why did the comet break apart?
 Q2.4: What are the sizes of the fragments?
 Q2.5: How long is the fragment train?
 Q2.6: Will Hubble or Galileo be able to observe the collisions?
 Q2.7: How can I observe the effects of the collisions?
 Q2.8: To whom do I report my observations?


GENERAL QUESTIONS

Q1.1: Is it true that a comet will collide with Jupiter in July 1994?

     Yes, the shattered comet Shoemaker-Levy 9 (1993e) is expected to collide
with Jupiter over a 5.6 day period in July 1994.  The first of 21 comet
fragments is expected to hit Jupiter on July 16, 1994 and the last on
July 22, 1994.  All components of the comet will hit on the dark farside
of Jupiter, out of sight from Earth.  The impact of the center of the comet
train is predicted to occur at about -44 degrees Jupiter latitude at a point
about 67 degrees east (toward the sunrise terminator) from the midnight
meridian.  The angle of incidence of the impacts is between 41 and 42
degrees for all the fragments.
     These new impact point estimates from Sekanina, Chodas, and Yeomans
are much closer to the morning terminator of Jupiter than the old estimates.
Although they are still all on the far side as viewed from the Earth, they are
now only 5-9 degrees behind the limb.  About 20 - 40 minutes after each hit,
the impact points will rotate past the limb of Jupiter as seen from Earth.
After these points cross the limb it will take another 17 minutes before
they cross the morning terminator into sunlight.

Q1.2: Who are Shoemaker and Levy?

     Eugene and Carolyn Shoemaker and David H. Levy found the 13.8 magnitude
comet on March 25, 1993 on photographic plates taken on March 22, 1993.  The
photographs were taken at Palomar Mountain in Southern California with a
0.46 meter Schmidt camera and were examined using a stereomicroscope to
reveal the comet [2,14].  James V. Scotti confirmed their discovery with the
Spacewatch Telescope at Kitt Peak in Arizona.  See [11] for more information
about the discovery.

Q1.3: Where can I find a GIF image of this comet?

     Some GIF images can be obtained via anonymous ftp from tamsun.tamu.edu
in the /pub/comet directory.  The GIF images here are named SL9*.GIF.
Also there are a some Hubble Space Telescope images at ftp.cicb.fr in the
/pub/Images/ASTRO/hst directory.  The GIF images here are named 1993e*.GIF.
See also seds.lpl.arizona.edu in the /pub/astro/SL9 directory.
     GIF files showing depictions of the Comet Shoemaker-Levy 9 impact
with Jupiter are available at the JPL Info public access computer site.
The files are in the /news directory and are named:

    SL9REND.GIF     Rendering 3 views of comet-Jupiter collision
    SL9REND1.GIF    Larger rendering comet-Jupiter from Earth
    SL9REND2.GIF    Larger rendering comet-Jupiter from Voyager 2
    SLREND3.GIF     Larger rendering comet-Jupiter from south pole

The renderings were made available on 9-Feb-1994 and were created by
David Seal of JPL based on data from Drs. Donald Yeomans and Paul Chodas.
The JPL Info site may be accessed by Internet anonymous ftp to
jplinfo.jpl.nasa.gov (137.78.104.2), or by dialup modem
to +1 (818) 354-1333.

Q1.4: What will be the effect of the collision?

     Each comet fragment will enter the atmosphere at a speed of 130,000 mph
(60 km/s).  At an altitude of 100 km above the visible cloud decks,
aerodynamic forces will overwhelm the material strength of the comet,
beginning to squeeze it and tear it apart.  Five seconds after entry, the
comet fragment will deposit its kinetic energy of around 10^28 ergs
(equivalent to around 200,000 megatons of TNT) at 100-150 km below the
cloud layer [19].  Bigger fragments will have more energy and go deeper.
     The hot (30,000 K) gas resulting from the stopped comet will explode,
forming a fireball similar to a nuclear explosion, but much larger.
The visible fireball will only rise 100 km or so above the cloudtops.
Above that height the density will drop so that it will become transparent.
The fireball material will continue to rise, reaching a height of perhaps
1000 km before falling back down to 300 km.  The fireball will spread out
over the top of the stratosphere to a radius of 2000-3000 km from the point
of impact (or so the preliminary calculations say).  The top of the resulting
shock wave will accelerate up out of the Jovian atmosphere in less than two
minutes, while the fireball will be as bright as the entire sunlit surface of
Jupiter for around 45 sec [18].  The fireball will be somewhat red, with a
characteristic temperature of 2000 K - 4000 K (slightly redder than the sun,
which is 5000 K).  Virtually all of the shocked cometary material will rise
behind the shock wave, leaving the Jovian atmosphere and then splashing back
down on top of the stratosphere at an altitude of 300 km above the clouds
[unpublished simulations by Mac Low & Zahnle].  Not much mass is involved in
this splash, so it will not be directly observable.  The splash will be
heavily enriched with cometary volatiles such as water or ammonia, and so may
contribute to significant high hazes.
        Meanwhile, the downward moving shock wave will heat the local clouds,
causing them to buoyantly rise up into the stratosphere.  This will allow
spectroscopists to attempt to directly study cloud material, a unique
opportunity to confirm theories of the composition of the Jovian clouds.
Furthermore, the downward moving shock may drive seismic waves (similar to
those from terrestrial earthquakes) that might be detected over much of the
planet by infrared telescopes in the first hour or two after each impact.
The strength of these two effects remains a topic of research.
        Finally, the disturbance of the atmosphere will drive internal
gravity waves ("ripples in a pond") outwards.  Over the days following the
impact, these waves will travel over much of the planet, yielding information
on the structure of the atmosphere if they can be observed (as yet an
open question).
     The "wings" of the comet will interact with the planet before and
after the collision of the major fragments.  The so-called "wings" are
defined to be the distinct boundary along the lines extending in both
directions from the line of the major fragments; some call these 'trails'.
Sekanina, Chodas and Yeomans have shown that the trails consist of larger
debris, not dust: 5-cm rock-sized material and bigger (boulder-sized and
building-sized).  Dust gets swept back above (north) of the trail-fragment
line due to solar radiation pressure.  The tails emanating from the major
fragments consist of dust being swept in this manner.  Only the small portion
of the eastern debris trail nearest the main fragments will actually impact
Jupiter, according to the model, with impacts starting only a week before
the major impacts.  The western debris trail, on the other hand, will impact
Jupiter over a period of months following the main impacts, with the latter
portion of the trail actually impacting on the front side of Jupiter as viewed
from Earth.
        The injection of dust from the wings and tail into the Jovian system
may have several consequences.  First, the dust will absorb many of the
energetic particles that currently produce radio emissions in the Jovian
magnetosphere.  The expected decline and recovery of the radio emission may
occur over as long as several years, and yield information on the nature and
origin of the energetic particles.  Second, the dust may actually form a
second faint ring around the planet.
     There are now two technical papers [18,19] on the atmospheric consequences
of the explosions available via anonymous ftp from oddjob.uchicago.edu in the
pub/jupiter directory.  The paper and figures are available in UNIX compressed
Postscript format; a couple of the computational figures are also available
in TIFF format.


SPECIFICS

Q2.1: What are the impact times and impact locations of the comet fragments?

     The following table gives the latest impact predictions.  A letter
designation for the cometary fragments has become standard. The 21 major
fragments are denoted A through W in order of impact, with letters I and O
not used. Fragment A is the closest to Jupiter and will impact first;
fragment W is the farthest and will impact last; fragment Q is the brightest
(and therefore presumably biggest), with G, H, K, L, and S also quite bright.

Predictions as of 1994 January 19
P.W. Chodas, D.K. Yeomans and Z. Sekanina
JPL/Caltech

+=============================================================================+
| Fragment  UT Date/Hour  Jovicentric  Meridian Angle   Angle  Probability of |
|            of Impact     Latitude     Angle   S-F-J   E-J-F  viewing impact |
|          month dy hr mn    (deg)      (deg)   (deg)   (deg)  Io  Eu  Ga  Ca |
+=============================================================================+
|  A = 21   July 16 19      -43.26      64.43   73.95   98.73   0   3   3   3 |
|  B = 20   July 17 03      -43.34      64.73   74.18   98.49   3   3   3   3 |
|  C = 19   July 17 06      -43.37      64.90   74.30   98.36   3   2   3   3 |
|  D = 18   July 17 12      -43.42      65.11   74.46   98.20   3   0   3   3 |
|  E = 17   July 17 14      -43.91      59.66   70.99  101.90   1   0   3   3 |
|  F = 16   July 18 00      -43.53      65.65   74.87   97.78   0   0   3   3 |
|  G = 15   July 18 07      -43.90      65.32   74.77   97.93   0   0   3   3 |
|  H = 14   July 18 19      -43.85      66.24   75.38   97.28   3   0   0   3 |
|  J = 13   July 19 02      -43.74      66.77   75.71   96.92   3   0   0   3 |
|  K = 12   July 19 10      -43.99      67.21   76.09   96.56   0   3   0   3 |
|  L = 11   July 19 23      -44.15      67.51   76.34   96.31   0   3   0   3 |
|  M = 10   July 20 06      -43.92      67.99   76.60   96.01   0   3   0   3 |
|  N = 9    July 20 10      -43.95      68.18   76.73   95.87   0   3   0   3 |
|  P = 8    July 20 15      -43.97      68.40   76.89   95.71   3   3   0   3 |
|  Q = 7    July 20 19      -44.29      67.35   76.27   96.39   3   3   0   3 |
|  R = 6    July 21 07      -44.14      79.28   79.28   93.26   1   0   0   3 |
|  S = 5    July 21 16      -44.62      68.71   77.30   95.37   0   0   0   3 |
|  T = 4    July 21 18      -44.10      69.63   77.77   94.80   0   0   0   3 |
|  U = 3    July 21 21      -44.11      69.77   77.88   94.69   0   0   0   3 |
|  V = 2    July 22 04      -44.14      70.09   78.11   94.46   0   0   0   3 |
|  W = 1    July 22 08      -44.20      69.92   78.00   94.57   2   0   0   3 |
+=============================================================================+
| Approximate                                                                 |
| Uncertainty   43 min        0.6        2.5     1.6     1.7                  |
|  (1-sigma)                                                                  |
+=============================================================================+

Table Notes:

*  Two fragment designations are given: the letter designation is that used
   in our preprint (Sekanina, Chodas, and Yeomans); the numerical designation
   is that used by Jewitt.  Q=7 is the brightest.

*  The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.

*  Angle S-F-J is the Sun-Fragment-Jupiter angle at impact; values less than
   90 deg indicate a nightside impact: all impacts are on the nightside.

*  Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact: all impacts are on the farside as
   viewed from Earth, with the later impacts being closer to the limb.

*  The predictions for fragments E and R are more uncertain than those for
   G, H, K, L, Q, S, and W, because the orbits are less well-determined.

*  The most recent measurements included in the orbit solutions were taken
   on Jan. 4 for fragments E and R, Jan. 9 for fragment S, and Jan. 10 for
   fragments G, H, K, L, Q, and W.

*  The impact times above include the light time to the Earth.

*  The probability that a given Galilean satellite will be in view of an
   impact is given in terms of sigmas: 0 indicates a probability of less than
   68%, 1 indicates 69-95%, 2 indicates 96-99%, and 3 indicates a probability
   greater than 99%.  For example, the probabilities that Io, Europa, and
   Callisto will be in view of the fragment Q impact are all greater than 99%.

*  The one-sigma uncertainties specified on the bottom line are average values
   obtained from Monte Carlo analyses for the eight fragments having the best
   orbit solutions.  The same analyses computed the probability that the
   fragments will in fact impact Jupiter is > 99.99%, and the probability that
   any will impact on the near side as viewed from the Earth is < 0.2%.

   See the Postscript file impact.ps at tamsun.tamu.edu in the /pub/comet
directory for a graph with impact times and Galilean moon eclipses.   The
following are the 3-sigma (uncertainty) predictions for the fragment impact
times:
          on March 1         -  90 min
          on May 1           -  71 min
          on June 1          -  49 min
          on July 1          -  30 min
          on July 15         -  19 min
          at impact - 18 hr  -  10 min

The time between impacts is thought to be known with more certainty than the
actual impact times.  This means that if somehow the impact time of the first
fragment can be measured experimentally, then impact times of the fragments
that follow can be predicted with more accuracy.

Q2.2: What are the orbital parameters of the comet?

   Comet Shoemaker-Levy 9 is actually orbiting Jupiter, which is most
unusual: comets usually just orbit the Sun.  Only two comets have ever
been known to orbit a planet (Jupiter in both cases), and this was inferred
in both cases by extrapolating their motion backwards to a time before they
were discovered.  S-L 9 is the first comet observed while orbiting a planet.
Shoemaker-Levy 9's previous closest approach to Jupiter (when it broke up)
was on July 7, 1992 according to the new solution; the distance from the
center of Jupiter was about 96,000 km, or about 1.3 Jupiter radii.  The comet
is thought to have reached apojove (farthest from Jupiter) on July 14, 1993
at a distance of about 0.33 Astronomical Units from Jupiter's center.  The
orbit is very elliptical, with an eccentricity of over 0.995.  Computations
by Paul Chodas, Zdenek Sekanina, and Don Yeomans, suggest that the comet has
been orbiting Jupiter for 20 years or more, but these backward extrapolations
of motion are highly uncertain.
     See [14] for a visual representation of the orbit.  The right ascension
and declination of the comet along with some orbital elements can be obtained
via ftp at tamsun.tamu.edu in the /pub/comet directory in the file called
elements.nuc.

Q2.3: Why did the comet break apart?

     The comet is thought to have broken apart due to tidal forces on its
closest approach to Jupiter (perijove) on July 7, 1992.  Shoemaker-Levy 9 is
not the first comet observed to break apart.  Comet West shattered in 1976
near the Sun [3].  Astronomers believe that in 1886 Comet Brooks 2 was ripped
apart by tidal forces near Jupiter [2].
     Furthermore, images of Callisto and Ganymede show crater chains which may
have resulted from the impact of a comet similar to Shoemaker-Levy 9 [3,17].
The satellite with the best example of aligned craters is Callisto with 13
crater chains.  There are three crater chains on Ganymede.  These were first
thought to be from basin ejecta; in other words secondary craters.  There are
also a few examples on our Moon.  Davy Catena for example, which may have been
due to comets split by Earth.

Q2.4: What are the sizes of the fragments?

     Using measurements of the length of the train of fragments and a model
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the
parent nucleus of the comet (before breakup) was only about 2 km across [13].
This would imply that the individual fragments are no larger than about 500
meters across.  However, images of the comet taken with the Hubble Space
Telescope in July 1993 indicate that the fragments are 3-4 km in diameter
(3-4 km is an upper limit based on their brightness).  A more elaborate tidal
disruption model by Sekanina, Chodas and Yeomans [20] predicts that the
original comet nucleus was at least 10 km in diameter.  This means the largest
fragments could be 3-4 km across, a size consistent with estimates derived
from the Hubble Space Telescope's observations.

Q2.5: How long is the fragment train?

     The angular length of the train was about 51 arcseconds in March 1993 [2].
The length of the train then was about one half the Earth-Moon distance.
In the day just prior to impact, the fragment train will stretch across 20
arcminutes of the sky, more that half the Moon's angular diameter.  This
translates to a physical length of about 5 million kilometers.  The train
expands in length due to differential orbital motion between the first and
last fragments.  Below is a table with data on train length based on Sekanina,
Chodas, and Yeomans's tidal disruption model:

           +=============================================+
           |    Date    Angular Length  Physical Length  |
           |               (arcsec)          (km)        |
           +=============================================+
           |  93 Mar 25       49            158,000      |
           |     Jul  1       67            265,000      |
           |  94 Jan  1      131            584,000      |
           |     Feb  1      161            669,000      |
           |     Mar  1      200            762,000      |
           |     Apr  1      255            893,000      |
           |     May  1      319          1,070,000      |
           |     Jun  1      400          1,366,000      |
           |     Jul  1      563          2,059,000      |
           |     Jul 15      944          3,593,000      |
           |    Impact A    1286          4,907,000      |
           +=============================================+


Q2.6: Will Hubble or Galileo be able to observe the collisions?

     The Hubble Space Telescope, like earthlings, will not be able to see the
collisions but will be able to monitor atmospheric changes on Jupiter. The new
impact points are more favorable for viewing from spacecraft: it can now be
stated with certainty that the impacts will all be visible to Galileo, and now
at least some impacts will be visible to Ulysses.  Although Ulysses does not
have a camera, it will monitor the impacts at radio wavelengths.  The impact
points are also viewable by both Voyager spacecraft, especially Voyager 2.
However, it is doubtful that the Voyagers will image the impacts because the
onboard software that controls the cameras has been deleted, and there is
insufficient time to restore and test the camera software.  The only Voyager
instruments likely to observe the impacts are the ultraviolet spectrometer
and planetary radio astronomy instrument.  Voyager 1 will be 52 AU from
Jupiter and will have a near-limb observation viewpoint.  Voyager 2 will be in
a better position to view the collision from a perspective of looking directly
down on the impacts, and it is also closer at 41 AU.
        Galileo will get a direct view of the impacts rather than the grazing
limb view previously expected.  The Ida image data playback is scheduled to
end at the end of June, so there should be no tape recorder conflicts with
observing the comet fragments colliding with Jupiter.  The problem is how to
get the most data played back when Galileo will only be transmitting at 10 bps.
One solution is to have both Ulysses and Galileo record the event and and store
the data on their respective tape recorders.  Ulysses observations of radio
emissions data will be played back first and will at least give the time of
each comet fragment impact.  Using this information, data can be selectively
played back from Galileo's tape recorder.  From Galileo's perspective, Jupiter
will be 60 pixels wide and the impacts will only show up at about 1 pixel,
but valuable science data can still collected in the visible and IR spectrum
along with radio wave emissions from the impacts.

Q2.7: How can I observe the effects of the collisions?

     One might be able to detect atmospheric changes on Jupiter using
photography, or CCD imaging.  It is important, however, to observe Jupiter
for several months in advance in order to know which features are due to comet
impacts and which are naturally occurring.  It appears more and more likely
that most effects will be quite subtle.  Without a large ( > 15" ?) telescope
and good detector, little is likely to be seen.  There is a MSDOS program
written by Lenny Abbey that displays information about Jupiter's major
features and predicts the locations of Jupiter's moons, the Great Red Spot,
and the central meridian System I and System II longitudes.  See the file
called jupe.description in tamsun.tamu.edu in the /pub/comet directory
for more information about this program.
     One may be able to witness the collisions indirectly by monitoring the
brightness of the Galilean moons that may be behind Jupiter as seen from
Earth.  However, current calculations suggest that the brightenings may
be as little as 0.05% of the sunlit brightness of the moon [18].  If Io can
be caught in eclipse but visible from the earth during an impact, prospects
will improve significantly.  The new version of the MSDOS program GALSAT51
will calculate and display the locations of the Galilean satellites for the
predicted impact times and can be obtained via ftp from tamsun.tamu.edu in
the /pub/comet directory.  One could monitor the moons using a photometer,
a CCD camera, or a video camera pointed directly into the eyepiece of a
telescope.  If you do video you can get photometric information by frame
grabbing and treating these like CCD frames (applying darks, biases, and
flats) [23].
     The cutoff of radio emissions due to the entry of cometary dust into the
Jovian magnetosphere during the weeks around impact may be clear enough to be
detected by small radio telescopes.  Furthermore, impacts may be directly
detectable in radio frequencies.  Some suggest to listen in on 15-30 MHz during
the comet impact, but to avoid 27 MHz because this frequency is used for CB
communications (ALPO conference, August 1993).  So it appears that one could
use the same antenna for both the Jupiter/Io phenomenon and the Jupiter/comet
impact.  There is an article in Sky & Telescope magazine which explains how to
build a simple antenna for observing the Jupiter/Io interaction [4].  See the
file called io_jup.radio on tamsun.tamu.edu in the /pub/comet directory for
more information.

Q2.8: To whom do I report my observations?

   The Association of Lunar and Planetary Observers (ALPO) will distribute a
handbook to interested observers.  The handbook "The Great Crash of 1994" is
available for $10 by
                        ALPO Jupiter Recorder
                        Phillip W. Budine
                        R.D. 3, Box 145C
                        Walton, NY 13856 U.S.A.

The cost includes printing, postage and handling.
     Observation forms by Steve Lucas are available via ftp at tamsun.tamu.edu
in the /pub/comet directory.  These forms also contain addresses of "Jupiter
Watch Program" section leaders.   JUPCOM.ZIP contains Microsoft Write files.
For other addresses see page 44 of the January 1994 issue of Sky & Telescope
magazine [14].


REFERENCES

 [1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
 [2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
       page 38-39.
 [3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
       chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
 [4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
 [5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
 [6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
 [7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
 [8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
       September 1993, page 18.
 [9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
 [10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
 [11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
 [12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
       of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
 [13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
       Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
 [14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
       January 1994, page 40-44.
 [15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
 [16] "AstroNews", Astronomy, January 1994, page 19.
 [17] "AstroNews", Astronomy, February 1994, page 16.
 [18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
       Comet Shoemaker Levy 9", submitted to Icarus October 29, 1993.
 [19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
       Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
       submitted to Nature January 7, 1994.
 [20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the
       Appearance of Periodic Comet Shoemaker-Levy 9", submitted to Astronomical
       Journal, November 1993.
 [21] "On a collision Course with Jupiter", Mercury, Nov-Dec 1993, page 15-16.
 [22] "Timing the Crash", Sky & Telescope, February 1994, page 11.
 [23] "Capturing Jupiter on Video" Sky & Telescope, September 1993, page 102.


ACKNOWLEDGMENTS

     Thanks to Ross Smith for starting a FAQ and to all those who have
contributed :  Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke, Rik Hill,
Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke, David H. Levy,
Eugene and Carolyn Shoemaker, Jim Scotti, Richard A. Schumacher,
Louis A. D'Amario, John McDonald, Michael Moroney, Byron Han, Wayne Hayes,
David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki, Jeffrey A Foust,
Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina, Don Yeomans,
Richard Schmude, and Lenny Abbey.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date:     Mon, 14 Feb 94 03:36 CST
% From: <WDB3926%[email protected]>
% Subject:  Comet/Jupiter Collision FAQ

    	The latest Hubble image of Comet SL-9 may be found at:
    
    	PRAGMA::PUBLIC:{NASA]HST_SL9*.*
    

Article: 53897
From: [email protected] (Chris Lewicki - LPL)
Newsgroups: sci.astro
Subject: New SL9 Images Available
Date: 8 Mar 1994 06:51:30 GMT
Organization: SEDS
 
	Previously unreleased ground images of "comet" P/Shoemaker-Levy 9
are now available at SEDS.LPL.Arizona.EDU.  The new material is located 
in /pub/astro/SL9. 

	 Note that this directory maybe be broken into subdirectories
sometime soon, as the amount of material here is getting rather large. 

	This material is accessible by gopher and FTP, and will (shortly) 
be available on the WWW. (http://SEDS.LPL.Arizona.EDU/)

	The images were converted from .tif's and care was taken to 
ensure that no "color-depth" was lost.   In order to aid in the viewing 
of the comet's dust trail try "inversing" the image. 
 
The index of the new files is included here:
 
sl03302b.gif	March 30, 1993 Image from Kitt Peak (J. Scotti)
sl03302b.txt	Description of sl03302b.gif
sl03302c.gif	Pseudo-color version of sl03302b.gif
sl90121.gif     January 21, 1994 Image from Kitt Peak (R. Jedicke)
sl90121x.gif	Enlarged view of sl90121.gif
sl90121.txt	Description of sl90121.gif
sl90216.gif	February 16, 1994 Image from Kitt Peak (J. Scotti)
sl90216s.gif	Gray-stretched inverse version of sl90216.gif
sl90216x.gif	Enlarged inverse version of sl90216.gif
sl90216.txt	Description of sl902161.gif
sl9compl.gif	Six month comparison image of SL9 (Labeled)
sl9comp.gif	Six month comparison image of SL9 (Not Labeled)
sl9comp.txt	Description of sl9comp.gif and sl9compl.gif
 
Enjoy!!!
 
---
-Chris Lewicki
[email protected]
Maintainer of SEDS.LPL.Arizona.EDU
'Legendary' Mars Observer GRS Flight Investigation Team
UA SEDS President
SEDS-USA Director of Special Projects
 

Article: 54068
From: [email protected]
Newsgroups: sci.astro,sci.space.science,alt.sci.planetary
Subject: was Leda SL9?
Date: 10 Mar 94 07:31:55 EDT
Organization: Social Science Computing Laboratory
 
In 1975, Charles Kowal at Palomar photographed an object thought to be a
new satellite of Jupiter.  It was seen several times, but not enough to
determine an orbit, then lost.  It was informally called Leda, and used
to show up as a footnote in texts of the late 70s.
 
It now looks as if SL9 could have been a temporary satellite of Jupiter
since the 70s.  Could 'Leda' have been an early observation of it during
one of its infrequent close passes? - not seen again because it was much
further out than anyone thought to look?  If so we might get a better idea
of SL9's pre-breakup size.  There might be a few other 'lost' satellite
observations to look for as well.
 
 
Phil Stooke
 

A post by Charles Kowal says that, in fact, Leda is not lost.  It is still in
orbit around Jupiter.  There was another body which Kowal found and subsequently
lost.  Howver, since it is lost, it has no name.  This could not be SL-9, Kowal
says, because it was far too dim.

Burns

Article: 54092
From: [email protected] (Charles Kowal,,4535)
Newsgroups: sci.astro,sci.space.science,alt.sci.planetary
Subject: Re: was Leda SL9?
Date: Fri, 11 Mar 1994 02:06:04 GMT
Organization: Space Telescope Science Institute
 
I found LEDA in 1974.  It is *not* lost!  Also known as J XIII, Leda
has a well-determined orbit. 
 
I found another possible satellite in 1975, which did get lost.  That
is the one you are probably referring to, but it is *not* called Leda.
Since it is lost, it was never given a name.  This object was much
fainter than Shoemaker-Levy, and I am sure there is no connection. 
 
-Charles Kowal
[email protected]
 

Article: 54162
From: [email protected] (William D. Sears)
Newsgroups: sci.astro,sci.space.science,alt.sci.planetary
Subject: Re: was Leda SL9?
Date: 11 Mar 1994 17:39:30 GMT
Organization: Lunar and Planetary Laboratory, University of Arizona
 
How much fainter?  S-L 9 may have been a very faint and very small
body before the breakup.  Have you discussed this with any of the
people doing the backward orbit integrations?  If thers is even a
small chance that you have a 'prediscovery' observation of S-L 9, I
know of several people who would be interested. 
 
I can get you in touch with some people, if you like, though I suspect
you can find them locally just as well. 
 
Wm.
 
Disclaimer: I'm just a grad student, currently working on tides,
though I would love to break into Asteroid work. I'll be graduating
this summer.... :) 
 
William D. Sears                | 'I reserve the right to ask irrelevant  
Lunar and Planetary Lab         |  questions, even impudent ones.          
[email protected]          |  You, of course, don't have to answer.'"    

From:	VERGA::US1RMC::"ASTRO%[email protected]" "Astronomy 
        Discussion List  18-Mar-1994 0701" 18-MAR-1994 06:55:44.31
To:	Multiple recipients of list ASTRO <ASTRO%[email protected]>
CC:	
Subj:	Re: Comet Shoemaker-Levy 9

There are recent elements for S-L 9 nuclei.

Hope that helps.

TP
--
03:40:31 Mar-18-1994 MET
______________________________________________________________________________

  Tomasz Plewa                          Internet: [email protected]
  Warsaw University Observatory         Bitnet:   [email protected]
  Al. Ujazdowskie 4                     phone :   (48 22) 294011..13
  00-478 Warsaw, Poland                 FAX:      (48 22) 294967
______________________________________________________________________________

------------------------------------------------------------------------------
M.P.E.C. 1994-D07                                Issued 1994 Feb. 20, 16:38 UT

     The Minor Planet Electronic Circulars contain information on unusual
         minor planets and routine data on comets.  They are published
   on behalf of Commission 20 of the International Astronomical Union by the
          Minor Planet Center, Smithsonian Astrophysical Observatory,
                          Cambridge, MA 02138, U.S.A.

          MARSDEN@CFA or WILLIAMS@CFA (.HARVARD.EDU, .SPAN or .BITNET)

                    PERIODIC COMET SHOEMAKER-LEVY 9 (1993e)

[ stuff deleted ]

Orbital elements:

Periodic Comet Shoemaker-Levy 9 (1993e) Nucleus T = 4

Epoch 1994 May 8.0 TT = JDT 2449480.5

T 1994 Mar. 30.85326 TT                                 Marsden
q   5.3797331            (2000.0)            P               Q
n   0.05592792     Peri.  354.97251     -0.80891369     +0.58419051
a   6.7720001      Node   221.00898     -0.53583604     -0.77888152
e   0.2055917      Incl.    5.78872     -0.24194709     -0.22817761
P  17.62

From 14 observations 1993 Mar. 27-1994 Feb. 14, mean residual 0".6.

Periodic Comet Shoemaker-Levy 9 (1993e) Nucleus U = 3

Epoch 1994 May 8.0 TT = JDT 2449480.5

T 1994 Mar. 31.87574 TT                                 Marsden
q   5.3791729            (2000.0)            P               Q
n   0.05598266     Peri.  355.03411     -0.80801170     +0.58544944
a   6.7675842      Node   221.03569     -0.53702508     -0.77798401
e   0.2051561      Incl.    5.77628     -0.24232447     -0.22801280
P  17.61

From 6 observations 1993 Mar. 27-1994 Feb. 14, mean residual 0".3.

Periodic Comet Shoemaker-Levy 9 (1993e) Nucleus V = 2

Epoch 1994 May 8.0 TT = JDT 2449480.5

T 1994 Mar. 31.96229 TT                                 Marsden
q   5.3792260            (2000.0)            P               Q
n   0.05603948     Peri.  355.01543     -0.80795463     +0.58553659
a   6.7630093      Node   221.05990     -0.53708924     -0.77787929
e   0.2046106      Incl.    5.76696     -0.24237259     -0.22814625
P  17.59

From 7 observations 1993 Mar. 27-1994 Feb. 14, mean residual 0".2.

Brian G. Marsden                                              M.P.E.C. 1994-D07
------------------------------------------------------------------------------

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date:         Fri, 18 Mar 1994 03:44:06 +0100
% Sender: Astronomy Discussion List <ASTRO%[email protected]>
% From: Tomasz Plewa <[email protected]>
% Organization: Warsaw University Astronomical Observatory
% Subject:      Re: Comet Shoemaker-Levy 9
% X-To:         [email protected]
% To: Multiple recipients of list ASTRO <ASTRO%[email protected]>

From:	VERGA::US4RMC::"WDB3926%[email protected]" "24-Mar-1994 
        2308" 24-MAR-1994 23:02:50.00
CC:	
Subj:	Comet/Jupiter Collision

 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *                                                                           *
 *                       Frequently Asked Questions about                    *
 *            the Collision of Comet Shoemaker-Levy 9 with Jupiter           *
 *                                                                           *
 *                         Last Updated 24-Mar-1994                          *
 *                          114 Days until Impact A                          *
 *                                                                           *
 *     The following is a list of answers to frequently asked questions      *
 * concerning the collision of comet Shoemaker-Levy 9 with Jupiter.  Thanks  *
 * to all those who have contributed.  Contact Dan Bruton ([email protected])   *
 * or John Harper ([email protected]) with comments, additions, corrections,  *
 * etc.  Updates of this FAQ list are available via anonymous ftp to         *
 * tamsun.tamu.edu (128.194.15.32) in the /pub/comet directory.              *
 *                                                                           *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Recent Changes to this FAQ List
===============================

        Question 1.3 : new GIF's and animations available
        Question 2.1 : new impact times, fragments J and M have disappeared
        Question 2.9 : FTP and WWW sites
       After the FAQ : Jovian Moon Events for late-March 1994


GENERAL QUESTIONS

 Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 Q1.2: Who are Shoemaker and Levy?
 Q1.3: Where can I find a GIF image of this comet?
 Q1.4: What will be the effect of the collision?


SPECIFICS

 Q2.1: What are the impact times and impact locations of the comet fragments?
 Q2.2: What are the orbital parameters of the comet?
 Q2.3: Why did the comet break apart?
 Q2.4: What are the sizes of the fragments?
 Q2.5: How long is the fragment train?
 Q2.6: Will Hubble or Galileo be able to observe the collisions?
 Q2.7: How can I observe the effects of the collisions?
 Q2.8: To whom do I report my observations?
 Q2.9: Where can I find more information?


GENERAL QUESTIONS

Q1.1: Is it true that a comet will collide with Jupiter in July 1994?

     Yes, the shattered comet Shoemaker-Levy 9 (1993e) is expected to collide
with Jupiter over a 5.6 day period in July 1994.  The first of 21 comet
fragments is expected to hit Jupiter on July 16, 1994 and the last on
July 22, 1994.  All components of the comet will hit on the dark farside
of Jupiter, out of sight from Earth.  The impact of the center of the comet
train is predicted to occur at about -44 degrees Jupiter latitude at a point
about 67 degrees east (toward the sunrise terminator) from the midnight
meridian.  The angle of incidence of the impacts is between 41 and 42
degrees for all the fragments.
     These new impact point estimates from Sekanina, Chodas, and Yeomans
are much closer to the morning terminator of Jupiter than the old estimates.
Although they are still all on the far side as viewed from the Earth, they are
now only 5-9 degrees behind the limb.  About 20 - 40 minutes after each hit,
the impact points will rotate past the limb of Jupiter as seen from Earth.
After these points cross the limb it will take another 17 minutes before
they cross the morning terminator into sunlight.


Q1.2: Who are Shoemaker and Levy?

     Eugene and Carolyn Shoemaker and David H. Levy found the 13.8 magnitude
comet on March 25, 1993 on photographic plates taken on March 22, 1993.  The
photographs were taken at Palomar Mountain in Southern California with a
0.46 meter Schmidt camera and were examined using a stereomicroscope to
reveal the comet [2,14].  James V. Scotti confirmed their discovery with the
Spacewatch Telescope at Kitt Peak in Arizona.  See [11] for more information
about the discovery.

Q1.3: Where can I find a GIF image of this comet?

     GIF images can be obtained via anonymous ftp to SEDS.LPL.Arizona.edu
(128.196.64.66) in the /pub/astro/SL9 directory.  Below is a list of the
images at this site.  The files are listed here in reverse chronological
order.  Most of the images are accompanied by a text file giving a
description of the image.

sl90216.gif      February 16, 1994 Image from Kitt Peak (J. Scotti)
sl90216s.gif     Gray-stretched inverse version of sl90216.gif
sl90216x.gif     Enlarged inverse version of sl90216.gif
wfpclevy.gif     Photo Montage of January 24-27 Imaging of SL9 from HST
sl9hst.gif       Post-fix HST Mosaic of SL9 (Jan. 24-27)
sl90121.gif      January 21, 1994 Image from Kitt Peak (R. Jedicke)
sl90121x.gif     Enlarged view of sl90121.gif
sl9compl.gif     Six month comparison image of SL9 (Labeled)
sl9comp.gif      Six month comparison image of SL9 (Not Labeled)
1993eha.gif      View of the comet from HST
1993ehb.gif      From HST, focused on the center of the train of fragments
1993esw.gif      Ground-based view of the comet
sl03302b.gif     March 30, 1993 Image from Kitt Peak (J. Scotti)
sl03302c.gif     Pseudo-color version of sl03302b.gif
sl9_930330.gif   March 30, 1993 image of SL9, Spacewatch Telescope-J. Scotti
sl9w_930328.gif  March 28, 1993 image of SL9
shoelevy.gif     An early GIF image of SL9

   The following is a list of other collision related GIF images and MPEG
animations that are also available at SEDS:

index.gif        Mosaic of all images in this directory
mitwave1.gif     Frame from MIT Flow Visualization Lab. Simulation
mitwave2.gif     Frame from MIT Flow Visualization Lab. Simulation
mitwave.mpg      MIT Flow Visualization Lab. Simulation Animation
vidjv.mpg        Animation of SL9 entering Jupiter's Atmosphere
visejz.mpg       Animation of explosion produced by SL9 entering Jupiter
sl9rend.gif      Rendering 3 views of comet-Jupiter collision
sl9rend1.gif     Larger rendering comet-Jupiter from Earth
sl9rend2.gif     Larger rendering comet-Jupiter from Voyager 2
sl9rend3.gif     Larger rendering comet-Jupiter from south pole
impact.gif       Graph of impact times with moon eclipses
wasserman.gif    Jupiter-Facing Hemispheres of Earth at Impact Times of SL9


Q1.4: What will be the effect of the collision?

     Each comet fragment will enter the atmosphere at a speed of 130,000 mph
(60 km/s).  At an altitude of 100 km above the visible cloud decks,
aerodynamic forces will overwhelm the material strength of the comet,
beginning to squeeze it and tear it apart.  Five seconds after entry, the
comet fragment will deposit its kinetic energy of around 10^28 ergs
(equivalent to around 200,000 megatons of TNT) at 100-150 km below the
cloud layer [19].  Bigger fragments will have more energy and go deeper.
     The hot (30,000 K) gas resulting from the stopped comet will explode,
forming a fireball similar to a nuclear explosion, but much larger.
The visible fireball will only rise 100 km or so above the cloudtops.
Above that height the density will drop so that it will become transparent.
The fireball material will continue to rise, reaching a height of perhaps
1000 km before falling back down to 300 km.  The fireball will spread out
over the top of the stratosphere to a radius of 2000-3000 km from the point
of impact (or so the preliminary calculations say).  The top of the resulting
shock wave will accelerate up out of the Jovian atmosphere in less than two
minutes, while the fireball will be as bright as the entire sunlit surface of
Jupiter for around 45 sec [18].  The fireball will be somewhat red, with a
characteristic temperature of 2000 K - 4000 K (slightly redder than the sun,
which is 5000 K).  Virtually all of the shocked cometary material will rise
behind the shock wave, leaving the Jovian atmosphere and then splashing back
down on top of the stratosphere at an altitude of 300 km above the clouds
[unpublished simulations by Mac Low & Zahnle].  Not much mass is involved in
this splash, so it will not be directly observable.  The splash will be
heavily enriched with cometary volatiles such as water or ammonia, and so may
contribute to significant high hazes.
        Meanwhile, the downward moving shock wave will heat the local clouds,
causing them to buoyantly rise up into the stratosphere.  This will allow
spectroscopists to attempt to directly study cloud material, a unique
opportunity to confirm theories of the composition of the Jovian clouds.
Furthermore, the downward moving shock may drive seismic waves (similar to
those from terrestrial earthquakes) that might be detected over much of the
planet by infrared telescopes in the first hour or two after each impact.
The strength of these two effects remains a topic of research.
        Finally, the disturbance of the atmosphere will drive internal
gravity waves ("ripples in a pond") outwards.  Over the days following the
impact, these waves will travel over much of the planet, yielding information
on the structure of the atmosphere if they can be observed (as yet an
open question).
     The "wings" of the comet will interact with the planet before and
after the collision of the major fragments.  The so-called "wings" are
defined to be the distinct boundary along the lines extending in both
directions from the line of the major fragments; some call these 'trails'.
Sekanina, Chodas and Yeomans have shown that the trails consist of larger
debris, not dust: 5-cm rock-sized material and bigger (boulder-sized and
building-sized).  Dust gets swept back above (north) of the trail-fragment
line due to solar radiation pressure.  The tails emanating from the major
fragments consist of dust being swept in this manner.  Only the small portion
of the eastern debris trail nearest the main fragments will actually impact
Jupiter, according to the model, with impacts starting only a week before
the major impacts.  The western debris trail, on the other hand, will impact
Jupiter over a period of months following the main impacts, with the latter
portion of the trail actually impacting on the front side of Jupiter as viewed
from Earth.
        The injection of dust from the wings and tail into the Jovian system
may have several consequences.  First, the dust will absorb many of the
energetic particles that currently produce radio emissions in the Jovian
magnetosphere.  The expected decline and recovery of the radio emission may
occur over as long as several years, and yield information on the nature and
origin of the energetic particles.  Second, the dust may actually form a
second faint ring around the planet.
     There are now two technical papers [18,19] on the atmospheric consequences
of the explosions available via anonymous ftp from oddjob.uchicago.edu in the
pub/jupiter directory.  The paper and figures are available in UNIX compressed
Postscript format; a couple of the computational figures are also available
in TIFF format.


SPECIFICS

Q2.1: What are the impact times and impact locations of the comet fragments?

     The following table gives the latest impact predictions.  The 21 major
fragments are denoted A through W in order of impact, with letters I and O
not used.  The predicted impact times for F, G, K, Q, R, and W have moved
slightly later (by up to 0.02 days), while those for H, L, and P are now
slightly earlier.  The impact points have generally moved a few tenths of a
degree closer to the limb as seen from the Earth.  Fragments J and M have
been deleted from the table because they have disappeared: they are not
visible in the HST image taken in late January.

Predictions as of 1994 February 23 by
P.W. Chodas, D.K. Yeomans and Z. Sekanina
JPL/Caltech

+=============================================================================+
| Fragment  UT Date/Hour  Jovicentric  Meridian Angle   Angle  Probability of |
|            of Impact     Latitude     Angle   S-F-J   E-J-F  viewing impact |
|          month dy hr mn    (deg)      (deg)   (deg)   (deg)  Io  Eu  Ga  Ca |
+=============================================================================+
|  A = 21   July 16 19      -43.26      64.43   73.95   98.73   0   3   3   3 |
|  B = 20   July 17 03      -43.34      64.73   74.18   98.49   3   3   3   3 |
|  C = 19   July 17 06      -43.37      64.90   74.30   98.36   3   2   3   3 |
|  D = 18   July 17 12      -43.42      65.11   74.46   98.20   3   0   3   3 |
|  E = 17   July 17 15      -43.80      64.98   74.50   98.21   1   0   3   3 |
|  F = 16   July 18 00      -44.24      63.09   73.40   99.42   0   0   3   3 |
|  G = 15   July 18 07      -44.19      65.00   74.66   98.09   0   0   3   3 |
|  H = 14   July 18 19      -44.04      64.99   74.60   98.13   3   0   0   3 |
|  J = 13   Disappeared                                                       |
|  K = 12   July 19 10      -44.43      66.16   75.51   97.22   0   3   0   3 |
|  L = 11   July 19 21      -44.52      65.60   75.17   97.58   0   3   0   3 |
|  M = 10   Disappeared                                                       |
|  N = 9    July 20 10      -44.78      66.40   75.79   96.97   0   3   0   3 |
|  P = 8    July 20 15      -45.00      65.61   75.34   97.47   3   3   0   3 |
|  Q = 7    July 20 19      -44.54      67.56   76.50   96.19   3   3   0   3 |
|  R = 6    July 21 07      -44.78      70.07   78.27   94.39   1   0   0   3 |
|  S = 5    July 21 15      -44.69      68.07   76.89   95.80   0   0   0   3 |
|  T = 4    July 21 18      -44.10      69.63   77.77   94.80   0   0   0   3 |
|  U = 3    July 21 21      -44.11      69.77   77.88   94.69   0   0   0   3 |
|  V = 2    July 22 04      -44.14      70.09   78.11   94.46   0   0   0   3 |
|  W = 1    July 22 08      -44.24      70.69   78.55   94.02   2   0   0   3 |
+=============================================================================+
| Approximate                                                                 |
| Uncertainty   43 min        0.6        2.5     1.6     1.7                  |
|  (1-sigma)                                                                  |
+=============================================================================+

Table Notes:

*  Two fragment designations are given: the letter designation is that used
   in a preprint (Sekanina, Chodas, and Yeomans); the numerical designation
   is that used by Jewitt.  Q=7 is the brightest.  Fragments J=13 and M=10
   have been deleted from the table because they are absent from the Hubble
   Space Telescope image taken in late January.  It is also now apparent from
   the HST image that P and Q each consist of two components.  In the above
   table, P refers to component P2=8b, the brighter and more easterly of the
   two P fragments, and Q refers to Q1=7a, the brighter and more southerly of
   the two Q fragments.

*  The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.

*  Angle S-F-J is the Sun-Fragment-Jupiter angle at impact; values less than
   90 deg indicate a nightside impact: all impacts are on the nightside.

*  Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact: all impacts are on the farside as
   viewed from Earth, with the later impacts being closer to the limb.

*  The predictions for fragments E and R are more uncertain than those for
   G, H, K, L, Q, S, and W, because the orbits are less well-determined.

*  The impact times above include the light time to the Earth (~ 43 minutes).

*  The probability that a given Galilean satellite will be in view of an
   impact is given in terms of sigmas: 0 indicates a probability of less than
   68%, 1 indicates 69-95%, 2 indicates 96-99%, and 3 indicates a probability
   greater than 99%.  For example, the probabilities that Io, Europa, and
   Callisto will be in view of the fragment Q impact are all greater than 99%.

*  The one-sigma uncertainties specified on the bottom line are average values
   obtained from Monte Carlo analyses for the eight fragments having the best
   orbit solutions.  The same analyses computed the probability that the
   fragments will in fact impact Jupiter is > 99.99%, and the probability that
   any will impact on the near side as viewed from the Earth is < 0.2%.

     The following are the 3-sigma (uncertainty) predictions for the
fragment impact times:

          on March 1         -  90 min
          on May 1           -  71 min
          on June 1          -  49 min
          on July 1          -  30 min
          on July 15         -  19 min
          at impact - 18 hr  -  10 min

The time between impacts is thought to be known with more certainty than the
actual impact times.  This means that if somehow the impact time of the first
fragment can be measured experimentally, then impact times of the fragments
that follow can be predicted with more accuracy.


Q2.2: What are the orbital parameters of the comet?

   Comet Shoemaker-Levy 9 is actually orbiting Jupiter, which is most
unusual: comets usually just orbit the Sun.  Only two comets have ever
been known to orbit a planet (Jupiter in both cases), and this was inferred
in both cases by extrapolating their motion backwards to a time before they
were discovered.  S-L 9 is the first comet observed while orbiting a planet.
Shoemaker-Levy 9's previous closest approach to Jupiter (when it broke up)
was on July 7, 1992 according to the new solution; the distance from the
center of Jupiter was about 96,000 km, or about 1.3 Jupiter radii.  The comet
is thought to have reached apojove (farthest from Jupiter) on July 14, 1993
at a distance of about 0.33 Astronomical Units from Jupiter's center.  The
orbit is very elliptical, with an eccentricity of over 0.995.  Computations
by Paul Chodas, Zdenek Sekanina, and Don Yeomans, suggest that the comet has
been orbiting Jupiter for 20 years or more, but these backward extrapolations
of motion are highly uncertain.
     See the Postscript plots called "fig*.ps" at SEDS.LPL.Arizona.EDU or [14]
for a visual representation of the orbit.  The right ascension and declination
of the comet along with some orbital elements can also be obtained via FTP at
SEDS.LPL.Arizona.EDU in the /pub/astro/SL9 directory in the file called
"elements.nuc".  This file is updated periodically.


Q2.3: Why did the comet break apart?

     The comet is thought to have broken apart due to tidal forces on its
closest approach to Jupiter (perijove) on July 7, 1992.  Shoemaker-Levy 9 is
not the first comet observed to break apart.  Comet West shattered in 1976
near the Sun [3].  Astronomers believe that in 1886 Comet Brooks 2 was ripped
apart by tidal forces near Jupiter [2].
     Furthermore, images of Callisto and Ganymede show crater chains which may
have resulted from the impact of a comet similar to Shoemaker-Levy 9 [3,17].
The satellite with the best example of aligned craters is Callisto with 13
crater chains.  There are three crater chains on Ganymede.  These were first
thought to be from basin ejecta; in other words secondary craters.  There are
also a few examples on our Moon.  Davy Catena for example, which may have been
due to comets split by Earth.


Q2.4: What are the sizes of the fragments?

     Using measurements of the length of the train of fragments and a model
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the
parent nucleus of the comet (before breakup) was only about 2 km across [13].
This would imply that the individual fragments are no larger than about 500
meters across.  However, images of the comet taken with the Hubble Space
Telescope in July 1993 indicate that the fragments are 3-4 km in diameter
(3-4 km is an upper limit based on their brightness).  A more elaborate tidal
disruption model by Sekanina, Chodas and Yeomans [20] predicts that the
original comet nucleus was at least 10 km in diameter.  This means the largest
fragments could be 3-4 km across, a size consistent with estimates derived
from the Hubble Space Telescope's July 1993 observations.
     The new images, taken with the Hubble telescope's  new  Wide  Field  and
Planetary  Camera-II instrument on January 24-27, 1994, have given us an even
clearer view of this fascinating  object, which should allow a refinement of
the size estimates.  In addition, the new images show strong evidence for
continuing fragmentation of some of the remaining nuclei, which will be
monitored by the Hubble telescope over the next several months.


Q2.5: How long is the fragment train?

     The angular length of the train was about 51 arcseconds in March 1993 [2].
The length of the train then was about one half the Earth-Moon distance.
In the day just prior to impact, the fragment train will stretch across 20
arcminutes of the sky, more that half the Moon's angular diameter.  This
translates to a physical length of about 5 million kilometers.  The train
expands in length due to differential orbital motion between the first and
last fragments.  Below is a table with data on train length based on Sekanina,
Chodas, and Yeomans's tidal disruption model:

           +=============================================+
           |    Date    Angular Length  Physical Length  |
           |               (arcsec)          (km)        |
           +=============================================+
           |  93 Mar 25       49            158,000      |
           |     Jul  1       67            265,000      |
           |  94 Jan  1      131            584,000      |
           |     Feb  1      161            669,000      |
           |     Mar  1      200            762,000      |
           |     Apr  1      255            893,000      |
           |     May  1      319          1,070,000      |
           |     Jun  1      400          1,366,000      |
           |     Jul  1      563          2,059,000      |
           |     Jul 15      944          3,593,000      |
           |    Impact A    1286          4,907,000      |
           +=============================================+


Q2.6: Will Hubble or Galileo be able to observe the collisions?

     The Hubble Space Telescope, like earthlings, will not be able to see the
collisions but will be able to monitor atmospheric changes on Jupiter. The new
impact points are more favorable for viewing from spacecraft: it can now be
stated with certainty that the impacts will all be visible to Galileo, and now
at least some impacts will be visible to Ulysses.  Although Ulysses does not
have a camera, it will monitor the impacts at radio wavelengths.  The impact
points are also viewable by both Voyager spacecraft, especially Voyager 2.
However, it is doubtful that the Voyagers will image the impacts because the
onboard software that controls the cameras has been deleted, and there is
insufficient time to restore and test the camera software.  The only Voyager
instruments likely to observe the impacts are the ultraviolet spectrometer
and planetary radio astronomy instrument.  Voyager 1 will be 52 AU from
Jupiter and will have a near-limb observation viewpoint.  Voyager 2 will be in
a better position to view the collision from a perspective of looking directly
down on the impacts, and it is also closer at 41 AU.
        Galileo will get a direct view of the impacts rather than the grazing
limb view previously expected.  The Ida image data playback is scheduled to
end at the end of June, so there should be no tape recorder conflicts with
observing the comet fragments colliding with Jupiter.  The problem is how to
get the most data played back when Galileo will only be transmitting at 10 bps.
One solution is to have both Ulysses and Galileo record the event and and store
the data on their respective tape recorders.  Ulysses observations of radio
emissions data will be played back first and will at least give the time of
each comet fragment impact.  Using this information, data can be selectively
played back from Galileo's tape recorder.  From Galileo's perspective, Jupiter
will be 60 pixels wide and the impacts will only show up at about 1 pixel,
but valuable science data can still collected in the visible and IR spectrum
along with radio wave emissions from the impacts.


Q2.7: How can I observe the effects of the collisions?

     One might be able to detect atmospheric changes on Jupiter using
photography, or CCD imaging.  It is important, however, to observe Jupiter
for several months in advance in order to know which features are due to
impacts and which are naturally occurring.  It appears more and more likely
that most effects will be quite subtle.  Without a large ( > 15" ?) telescope
and good detector, little is likely to be seen.  There is a MSDOS program
written by Lenny Abbey that displays information about Jupiter's major
features and predicts the locations of Jupiter's moons, the Great Red Spot,
and the central meridian System I and System II longitudes.  See the file
called "jupe.description" in tamsun.tamu.edu in the /pub/comet directory
for more information about this program.
     One may be able to witness the collisions indirectly by monitoring the
brightness of the Galilean moons that may be behind Jupiter as seen from
Earth.  However, current calculations suggest that the brightenings may
be as little as 0.05% of the sunlit brightness of the moon [18].  If Io can
be caught in eclipse but visible from the earth during an impact, prospects
will improve significantly.  The MSDOS program "galsat51.zip" will calculate
and display the locations of the Galilean satellites for the predicted impact
times and can be obtained via ftp from tamsun.tamu.edu in the /pub/comet
directory.  One could monitor the moons using a photometer, a CCD camera, or
a video camera pointed directly into the eyepiece of a telescope.  If you do
video you can get photometric information by frame grabbing and treating these
like CCD frames (applying darks, biases, and flats) [23].
     The cutoff of radio emissions due to the entry of cometary dust into the
Jovian magnetosphere during the weeks around impact may be clear enough to be
detected by small radio telescopes.  Furthermore, impacts may be directly
detectable in radio frequencies.  Some suggest to listen in on 15-30 MHz during
the comet impact.  So it appears that one could use the same antenna for both
the Jupiter/Io phenomenon and the Jupiter/comet impact.  There is an article
in Sky & Telescope magazine which explains how to build a simple antenna for
observing the Jupiter/Io interaction [4,24,25].  This simple antenna is less
directional that a dipole or long-wire antenna.  See the file called
"io_jup.radio" on tamsun.tamu.edu in the /pub/comet directory for more
information.  This file is updated periodically.


Q2.8: To whom do I report my observations?

   The Association of Lunar and Planetary Observers (ALPO) will distribute a
handbook to interested observers.  Also, observation forms by Steve Lucas are
available via ftp at tamsun.tamu.edu in the /pub/comet directory.  These
forms also contain addresses of "Jupiter Watch Program" section leaders.
"jupcom.zip" contains Microsoft Write files.  For addresses of ALPO, Steve
Lucas and other Jupiter recorders see the January 1994 issue of Sky &
Telescope magazine [14].


Q2.9: Where can I find more information?

===============================================================================
   FTP SITE NAME       IP ADDRESS       DIRECTORY              CONTENTS
===============================================================================
SEDS.LPL.Arizona.EDU (128.196.64.66)  /pub/astro/SL9         Images & Info
tamsun.tamu.edu      (128.194.15.32)  /pub/comet             Images & Info
oddjob.uchicago.edu                   /pub/jupiter           Article & figures
jplinfo.jpl.nasa.gov (137.78.104.2)   /news and /images      Images
ftp.cicb.fr          (129.20.128.34)  /pub/Images/ASTRO/hst  Images

===============================================================================
     WORLD WIDE WEB SITES                                         CONTENTS
===============================================================================
http://seds.lpl.arizona.edu/sl9/sl9.html                       Images and Info
http://pscinfo.psc.edu/general/research/mac_low/mac_low.html   Animations
http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html   Info and Images


REFERENCES

 [1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
 [2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
       page 38-39.
 [3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
       chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
 [4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
 [5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
 [6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
 [7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
 [8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
       September 1993, page 18.
 [9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
 [10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
 [11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
 [12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
       of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
 [13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
       Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
 [14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
       January 1994, page 40-44.
 [15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
 [16] "AstroNews", Astronomy, January 1994, page 19.
 [17] "AstroNews", Astronomy, February 1994, page 16.
 [18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
       Comet Shoemaker Levy 9", submitted to Icarus October 29, 1993.
 [19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
       Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
       submitted to Science on 10 February 1994.
 [20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the
       Appearance of Periodic Comet Shoemaker-Levy 9", submitted to Astronomical
       Journal, November 1993.
 [21] "On a collision Course with Jupiter", Mercury, Nov-Dec 1993, page 15-16.
 [22] "Timing the Crash", Sky & Telescope, February 1994, page 11.
 [23] "Capturing Jupiter on Video" Sky & Telescope, September 1993, page 102.
 [24] "Advanced Amateur Astronomy", Gerald North, (1991), page 296-298.
 [25] "Backyard Radio Astronomy", Astronomy, March 1983, page 75-77.


ACKNOWLEDGMENTS

     Thanks to Ross Smith for starting a FAQ and to all those who have
contributed :  Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke, Rik Hill,
Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke, David H. Levy,
Eugene and Carolyn Shoemaker, Jim Scotti, Richard A. Schumacher,
Louis A. D'Amario, John McDonald, Michael Moroney, Byron Han, Wayne Hayes,
David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki, Jeffrey A Foust,
Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina, Don Yeomans,
Richard Schmude, Lenny Abbey, Chris Lewicki, and the Students for the
Exploration and Development of Space (SEDS).

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *


Jovian Moon Events for March 1994

KEY:

+---------------------------------------------------------------+
|   SATELLITE                EVENT                 TYPE         |
+---------------------------------------------------------------+
|  I  -> Io               Tr -> Transit         D -> Disappear  |
| II  -> Europa           Sh -> Shadow          R -> Reappear   |
| III -> Ganymede         Ec -> Eclipse         I -> Ingress    |
| IV  -> Callisto         Oc -> Occult          E -> Egress     |
+---------------------------------------------------------------+

DESCRIPTION OF TABLE :

             Column 1 : Date
             Column 2 : Universal Time
             Column 3 : Satellite (I,II,III,IV)
             Column 4 : Transit, Shadow, Eclipse, or Occult
             Column 5 : Disappear, Reappear, Ingress or Egress


Jovian Moon Events for March 1994

Mar. 21
          5:24   I.Sh.I.
          6:16   I.Tr.I.
          7:34   I.Sh.E.
          8:24   I.Tr.E.
Mar. 22
          2:33   I.Ec.D.
          5:32   I.Oc.R.
          8:00  II.Sh.I.
          9:43  II.Tr.I.
         10:21  II.Sh.E.
         11:57  II.Tr.E.
         19:52 III.Ec.D.
         20:02 III.Ec.R.
         23:30 III.Oc.D.
         23:52   I.Sh.I.
Mar. 23
          0:42   I.Tr.I.
          1:05 III.Oc.R.
          2:02   I.Sh.E.
          2:50   I.Tr.E.
         21:01   I.Ec.D.
         23:58   I.Oc.R.
Mar. 24
          3:01  II.Ec.D.
          6:58  II.Oc.R.
         18:20   I.Sh.I.
         19:09   I.Tr.I.
         20:30   I.Sh.E.
         21:17   I.Tr.E.
Mar. 25
         15:29   I.Ec.D.
         18:25   I.Oc.R.
         21:17  II.Sh.I.
         22:52  II.Tr.I.
         23:37  II.Sh.E.
Mar. 26
          1:06  II.Tr.E.
          9:48 III.Sh.I.
         11:55 III.Sh.E.
         12:49   I.Sh.I.
         13:11 III.Tr.I.
         13:35   I.Tr.I.
         14:43 III.Tr.E.
         14:59   I.Sh.E.
         15:43   I.Tr.E.
Mar. 27
          9:58   I.Ec.D.
         12:51   I.Oc.R.
         16:19  II.Ec.D.
         20:08  II.Oc.R.
Mar. 28
          7:17   I.Sh.I.
          8:02   I.Tr.I.
          9:27   I.Sh.E.
         10:10   I.Tr.E.
Mar. 29
          4:26   I.Ec.D.
          7:18   I.Oc.R.
         10:34  II.Sh.I.
         12:01  II.Tr.I.
         12:54  II.Sh.E.
         14:15  II.Tr.E.
         23:50 III.Ec.D.
Mar. 30
          1:46   I.Sh.I.
          1:59 III.Ec.R.
          2:28   I.Tr.I.
          2:57 III.Oc.D.
          3:56   I.Sh.E.
          4:31 III.Oc.R.
          4:36   I.Tr.E.
         22:54   I.Ec.D.
Mar. 31
          1:44   I.Oc.R.
          5:36  II.Ec.D.
          9:17  II.Oc.R.
         20:14   I.Sh.I.
         20:55   I.Tr.I.
         22:24   I.Sh.E.
         23:03   I.Tr.E.

---

End of transmission...

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date:     Thu, 24 Mar 94 22:03 CST
% From: <WDB3926%[email protected]>
% Subject:  Comet/Jupiter Collision

Article: 55061
From: [email protected] (Mike Gingell)
Newsgroups: sci.astro
Subject: Re: SL9, Jupiter, and Radio
Date: 25 Mar 1994 18:58:05 GMT
Organization: Alcatel Network Systems, Raleigh, NC
 
In article <[email protected]>, Jim Sharpe <[email protected]> wrote:

>In <[email protected]>
[email protected] (Laurence Gene Battin) writes: 
>>Would there be any possibility that the impact of SL9 with Jupiter could have
>>an observable effect on the radio signals at 18-22 MHz which come from
>>Jupiter's vicinity?  In other words, will the explosions caused by the impact
>>be strong enough to affect the mechanisms that produce the radio signals?
>
>I would also be interested in hearing any responses to this.
 
Absolutely.  I have in my hands a copy of a paper entitled "Jovian
Encounter with Comet Shoemaker-Levy 9  -  July 1994" by the SARA (Soc
of Amateur Radio Astronomers) Jupiter Comet Watch Program.  For more
information contact T J Crowley, 3912 Whittington Drive, Atlanta GA
30342, 404-801-4405 day or 404-233-6886 evening. 
 
The paper details probable efects of the impact and suggests setups
for detecting them.  One section is entitled "Radio Equipment Required
to Monitor The Decametric Synchrotron Emissions"", basically an
antenna, a preamp, and any good short wave communications receiver.
Better still if you can have 2 receivers, one tuned to WWV for time
stamp information and record both signals in stereo. 
 
They are looking for observers, For more information contact T J
Crowley, 3912 Whittington Drive, Atlanta GA 30342, 404-801-4405 day or
404-233-6886 evening. 
 
Mike,  [email protected]    Raleigh, NC USA, (919) 850-6444 (day)
 

Article: 55372
Newsgroups: sci.astro
Subject: SHOEMAKER-LEVEY IMPACT PR
From: [email protected] (Mike Rushford)
Date: Tue, 29 Mar 94 18:48:00 +0000
Organization: Eyes BBS
 
@SUBJECT:Shoemaker-Levey impact prediction                           
  To Jim's SJAA news list --
 
    Here's a list of the SL9 / Jupiter times, from a posting by Jerry
Groninger (Anaheim) on the RIME astronomy echo.  His list had an
incorrect adjustment for PDT, which I've fixed here.  Happily for our
Arizona member, the same time zone applies. (Hi, Pete!) 
 
SHOEMAKER-LEVY  ---  PROJECTED IMPACT TIMES
  JULY 16-21, 1994, PACIFIC DAYLIGHT TIME
 
NUCLEUS  UNIVERSAL UNIV.  PDT   LOCAL TIME
           TIME    HOURS  DAY      (PDT)
~~~~~~~  ~~~~~~~~  ~~~~~  ~~~   ~~~~~~~~~~
    21   16  0.81  19.44   16    12:26 PM
    20   17  0.11   2.64   16     7:38 PM
    19   17  0.27   6.48   16    11:29 PM
    18   17  0.48  11.52   17     4:31 AM
    17   17  0.61  14.64   17     7:38 AM
    16   18  0.02   0.48   17     5:29 PM
    15   18  0.30   7.20   18    12:12 AM
    14   18  0.78  18.72   18    11:43 AM
    12   19  0.42  10.08   19     3:05 AM
    11   19  0.89  21.36   19     2:22 PM
     9   20  0.41   9.84   20     2:50 AM
     8   20  0.61  14.64   20     7:38 AM
     7   20  0.80  19.20   21    12:12 PM
     6   21  0.28   6.72   20    11:43 PM
     5   21  0.61  14.64   21     7:38 AM
     4   21  0.75  18.00   21    11:00 AM
     3   21  0.88  21.12   21     2:07 PM
     2   22  0.18   4.32   21     9:19 PM
     1   22  0.32   7.68   22    12:41 AM
 
 The 1-Sigma uncertainty is 0.03 days,
 approximately 43 minutes.
 
Jim Van Nuland
UUCP: amdahl.com!kennel!11!Jim.Van.Nuland
INTERNET: [email protected]
"The views expressed above are those of Jim Van Nuland only."
 
Cross posted from Internet mail on the Eyes on the Sky to this news
group by:
 
      Internet: [email protected] or [email protected]
      FINONET:  1:161/708; VECTORNET: 1:510/120
      BBS:      (510) 443-6146;  Office: (510) 423-2037
      Fax:      (510) 422-1930
      Latt:     37 40 11.5 N  Long: 121 44 48.3 W       KD6SNS
--- FidoPCB v1.5 beta-'e'
 * Origin: Eye' on the Sky 510-443-6146 has a telescope 4u2 use 1:161/1111

Article: 3433
From: [email protected] (Chris Lewicki)
Newsgroups: alt.com,alt.sci.planetary
Subject: SL9 Mailing List Available
Date: 5 Apr 1994 21:50:31 GMT
Organization: SEDS
 
	A new mailing list has been established for Comet
P/Shoemaker-Levy 9. This list is being provided in order to facilitate
the discussion of the impact of comet P/Shoemaker-Levy 9 with Jupiter
in July.  This list is not for the posting of images.  The SL9 list is
a result of the "overgrowth" of Dan Bruton's personally maintained
list at Texas A & M.  The list is unmoderated (unless problems arise)
and posts will be archived. 
 
To subscribe yourself to the SL9 list, send a message to:
 
[email protected]
 
with no subject, and the only line of the message:
 
SUBSCRIBE SL9 YOUR_FIRST_NAME YOUR_LAST_NAME
 
   You can also unsubscribe yourself from the list by sending the message:
 
UNSUBSCRIBE SL9
 
to the previous address.  
 
	You will be notified of more options once you have subscribed
to the list. 
---
-Chris Lewicki
[email protected]

Maintainer of SEDS.LPL.Arizona.EDU
'Legendary' Mars Observer GRS Flight Investigation Team
UA SEDS President
SEDS-USA Director of Special Projects
 

    A lengthy series of articles was released on the internet. The
    collective information is intended as background material for
    science teachers.
    
    This is quite a large file: over 2000 lines, so DECwindows Notes
    users should beware!
    
    Enjoy!
    
    Regards,
    
    John B.

Article: 5567
From: [email protected] (David M. Seidel)
Newsgroups: sci.space.news
Subject: JPL/Shoemaker-Levy 9 Introduction
Date: 14 Apr 1994 18:06:11 -0700
Organization: Jet Propulsion Laboratory
Sender: [email protected]
 
Background Material for Science Teachers
JULY 1994 -- Periodic Comet Shoemaker-Levy 9 Collides with Jupiter
 
Cover: Comet Shoemaker-Levy 9 is expected to collide with Jupiter 
in July 1994. From this historic event, scientists hope to learn 
more about comets, Jupiter, and the physics of high velocity 
planetary impacts.
 
For a period of about six days centered on JulyJ19, 1994, 
fragments of Comet Shoemaker-LevyJ9 are expected to collide with 
Jupiter, the solar systemUs largest planet. No such event has ever 
before been available for study. The energy released by the larger 
fragments during impact will be more than 10,000Jtimes the energy 
released by a 100-megaton hydrogen bomb! Unfortunately for 
observers, the collisions will occur on the night side of Jupiter, 
which also will be the back side as seen from Earth. The 
collisions can still be studied in many ways, nevertheless, by 
spacecraft more advantageously located, by light of the collisions 
reflected from JupiterUs satellites, and by the effects of the 
impacts upon the Jovian atmosphere. (The impact sites will rotate 
into view from Earth about 20Jminutes after each collision.) 
 
Stupendous as these collisions will be, they will occur on the far 
side of a body half a billion miles from Earth. There will be no 
display visible to the general public, not even a display as 
obvious as a faint terrestrial meteor. Amateur astronomers may 
note a few seconds of brightening of the inner satellites of 
Jupiter during the impacts, and they might observe minor changes 
in the Jovian cloud structure during the days following the 
impacts. The real value of this most unusual event will come from 
scientific studies of the cometUs composition, of the impact 
phenomena themselves, and of the response of a planetary 
atmosphere and magnetosphere to such a series of Rinsults.S
 
This booklet offers some background material on Jupiter, comets, 
what has and possibly will happen, and how scientists propose to 
take advantage of the impact events.
 
Contents
 
1.	What Is a Comet?
2.	The Motion of Comets
3.	The Fragmentation of Comets
4.	The Discovery and Early Study 
	of Shoemaker-Levy 9
5.	The Planet Jupiter	11
6.	The Final Orbit of Shoemaker-Levy 9
7.	The Collisions
8.	How Can These Impacts and Their 
	Consequences Be Studied?
9.	What Do Scientists Expect 
	to Learn from All of This?
 
Appendices
 
A.	Comparative Tables
B.	The K-T Event
C.	The Probability of Collisions with Earth
 
 
NOTE:  Diagrams and illustrations refered to in the text will be 
produced as GIF files in the near future.  When they become 
available, these text files will be reposted with them.
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
1. What is a Comet?
 
		Comets are small, fragile, irregularly shaped bodies 
composed of a mixture of non-volatile grains and frozen gases. 
They usually follow highly elongated paths around the Sun. Most 
become visible, even in telescopes, only when they get near enough 
to the Sun for the SunUs radiation to start subliming the volatile 
gases, which in turn blow away small bits of the solid material. 
These materials expand into an enormous escaping atmosphere called 
the coma, which becomes far bigger than a planet, and they are 
forced back into long tails of dust and gas by radiation and 
charged particles flowing from the Sun. Comets are cold bodies, 
and we see them only because the gases in their comae and tails 
fluoresce in sunlight (somewhat akin to a fluorescent light) and 
because of sunlight reflected from the solids. Comets are regular 
members of the solar system family, gravitationally bound to the 
Sun. They are generally believed to be made of material, 
originally in the outer part of the solar system, that didnUt get 
incorporated into the planets -- leftover debris, if you will. It 
is the very fact that they are thought to be composed of such 
unchanged RprimitiveS material that makes them extremely 
interesting to scientists who wish to learn about conditions 
during the earliest period of the solar system.
 
Comets are very small in size relative to planets. Their average 
diameters usually range from 750Jm or less to about 20Jkm. 
Recently, evidence has been found for much larger distant comets, 
perhaps having diameters of 300Jkm or more, but these sizes are 
still small compared to planets. Planets are usually more or less 
spherical in shape, usually bulging slightly at the equator. 
Comets are irregular in shape, with their longest dimension often 
twice the shortest. (See Appendix A, Table 3.) The best evidence 
suggests that comets are very fragile. Their tensile strength (the 
stress they can take without being pulled apart) appears to be 
only about 1,000Jdynes/cm2 (about 2Jlb./ft.2). You could take a 
big piece of cometary material and simply pull it in two with your 
bare hands, something like a poorly compacted snowball.
 
Comets, of course, must obey the same universal laws of motion as 
do all other bodies. Where the orbits of planets around the Sun 
are nearly circular, however, the orbits of comets are quite 
elongated. Nearly 100Jknown comets have periods (the time it takes 
them to make one complete trip around the Sun) five to seven Earth 
years in length. Their farthest point from the Sun (their 
aphelion) is near JupiterUs orbit, with the closest point 
(perihelion) being much nearer to Earth. A few comets like Halley 
have their aphelions beyond Neptune (which is six times as far 
from the Sun as Jupiter). Other comets come from much farther out 
yet, and it may take them thousands or even hundreds of thousands 
of years to make one complete orbit around the Sun. In all cases, 
if a comet approaches near to Jupiter, it is strongly attracted by 
the gravitational pull of that giant among planets, and its orbit 
is perturbed (changed), sometimes radically. This is part of what 
happened to Shoemaker-LevyJ9. (See SectionsJ2 andJ4 for more 
details.)
 
The nucleus of a comet, which is its solid, persisting part, has 
been called an icy conglomerate, a dirty snowball, and other 
colorful but even less accurate descriptions. Certainly a comet 
nucleus contains silicates akin to some ordinary Earth rocks in 
composition, probably mostly in very small grains and pieces. 
Perhaps the grains are RgluedS together into larger pieces by the 
frozen gases. A nucleus appears to include complex carbon 
compounds and perhaps some free carbon, which make it very black 
in color. Most notably, at least when young, it contains many 
frozen gases, the most common being ordinary water. In the low 
pressure conditions of space, water sublimes, that is, it goes 
directly from solid to gas -- just like dry ice does on Earth. 
Water probably makes up 75-80% of the volatile material in most 
comets. Other common ices are carbon monoxide (CO), carbon dioxide 
(CO2), methane (CH4), ammonia (NH3), and formaldehyde (H2CO). 
Volatiles and solids appear to be fairly well mixed throughout the 
nucleus of a new comet approaching the Sun for the first time. As 
a comet ages from many trips close to the Sun, there is evidence 
that it loses most of its ices, or at least those ices anywhere 
near the nucleus surface, and becomes just a very fragile old 
RrockS in appearance, indistinguishable at a distance from an 
asteroid.
 
A comet nucleus is small, so its gravitational pull is very weak. 
You could run and jump completely off of it (if you could get 
traction). The escape velocity is only about 1Jm/s (compared to 
11Jkm/s on Earth). As a result, the escaping gases and the small 
solid particles (dust) that they drag with them never fall back to 
the nucleus surface. Radiation pressure, the pressure of sunlight, 
forces the dust particles back into a dust tail in the direction 
opposite to the Sun. A cometUs tail can be tens of millions of 
kilometers in length when seen in the reflected sunlight. The gas 
molecules are torn apart by solar ultraviolet light, often losing 
electrons and becoming electrically charged fragments or ions. The 
ions interact with the wind of charged particles flowing out from 
the Sun and are forced back into an ion tail, which again can 
extend for millions of kilometers in the direction opposite to the 
Sun. These ions can be seen as they fluoresce in sunlight. 
 
Every comet then really has two tails, a dust tail and an ion 
tail. If the comet is faint, only one or neither tail may be 
detectable, and the comet may appear just as a fuzzy blob of 
light, even in a big telescope. The density of material in the 
coma and tails is very low, lower than the best vacuum that can be 
produced in most laboratories. In 1986 the Giotto spacecraft flew 
right through Comet Halley only a few hundred kilometers from the 
nucleus. Though the coma and tails of a comet may extend for tens 
of millions of kilometers and become easily visible to the naked 
eye in EarthUs night sky, as Comet WestUs were in 1976, the entire 
phenomenon is the product of a tiny nucleus only a few kilometers 
across.
 
Because comet nuclei are so small, they are quite difficult to 
study from Earth. They always appear at most as a point of light 
in even the largest telescope, if not lost completely in the glare 
of the coma. A great deal was learned when the European Space 
Agency, the Soviet Union, and the Japanese sent spacecraft to fly 
by Comet Halley in 1986. For the first time, actual images of an 
active nucleus were obtained (see FigureJ1) and the composition of 
the dust and gases flowing from it was directly measured. Early in 
the next century the Europeans plan to send a spacecraft called 
Rosetta to rendezvous with a comet and watch it closely for a long 
period of time. Even this sophisticated mission is not likely to 
tell scientists a great deal about the interior structure of 
comets, however. Therefore, the opportunity to reconstruct the 
events that occurred when Shoemaker-LevyJ9 split and to study 
those that will occur when the fragments are destroyed in 
JupiterUs atmosphere is uniquely important (see Sections 4, 7, and 
8).
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 
2. The Motion of Comets
 
		Comets necessarily obey the same physical laws as every 
other object. They move according to the basic laws of motion and 
of universal gravitation discovered by Newton in the 17th century 
(ignoring very small relativistic corrections). If one considers 
only two bodies -- either the Sun and a planet, or the Sun and a 
comet -- the smaller body appears to follow an elliptical path or 
orbit about the Sun, which is at one focus of the ellipse. The 
geometrical constants which fully define the shape of the ellipse 
are the semimajor axis a and the eccentricity e (see FigureJ2). 
The semiminor axis b is related to those two quantities by the 
equation bJ=JaC(1-e2). The focus is located a distance ae from the 
center of the ellipse. Three further constants are required if one 
wishes to describe the orientation of the ellipse in space 
relative to some coordinate system, and a fourth quantity is 
required if one wishes to define the location of a body in that 
elliptical orbit.
 
In FigureJ2B several ellipses are drawn, all having the same 
semimajor axis but different eccentricities. Eccentricity is a 
mathematical measure of departure from circularity. A circle has 
zero eccentricity, and most of the planets have orbits which are 
nearly circles. Only Pluto and Mercury have eccentricities 
exceeding 0.1. Comets, however, have very large eccentricities, 
often approaching one, the value for a parabola. Such highly 
eccentric orbits are just as possible as circular orbits, as far 
as the laws of motion are concerned.
 
The solar system consists of the Sun, nine planets, numerous 
satellites and asteroids, comets, and various small debris. At any 
given time the motion of any solar system body is affected by the 
gravitational pulls of all of the others. The SunUs pull is the 
largest by far, unless one body approaches very closely to 
another, so orbit calculations usually are carried out as two-body 
calculations (the body in question and the Sun) with small 
perturbations (small added effects due to the pull of other 
bodies). In 1705 Halley noted in his original paper predicting the 
return of RhisS comet that Jupiter undoubtedly had serious effects 
on the cometUs motion, and he presumed Jupiter to be the cause of 
changes in the period (the time required for one complete 
revolution about the Sun) of the comet. (Comet HalleyUs period is 
usually stated to be 76Jyears, but in fact it has varied between 
74.4Jand 79.2Jyears during the past 2,000Jyears.) In that same 
paper Halley also became the first to note the very real 
possibility of the collision of comets with planets, but stated 
that he would leave the consequences of such a RcontactS or 
RshockS to be discussed Rby the Studious of Physical Matters.S 
 
In the case of Shoemaker-Levy 9 we have the perfect example both 
of large perturbations and their possible Rconsequences.S The 
comet was fragmented and perturbed into an orbit where the pieces 
will hit Jupiter one period later. In general one must note that 
JupiterUs gravity (or that of other planets) is perfectly capable 
of changing the energy of a cometUs orbit sufficiently to throw it 
clear out of the solar system (to give it escape velocity from the 
solar system) and has done so on numerous occasions. See FigureJ3. 
This is exactly the same physical effect that permits using 
planets to change the orbital energy of a spacecraft in so-called 
Rgravity-assist maneuversS such as were used by the Voyager 
spacecraft to visit all the outer planets except Pluto.
 
One of NewtonUs laws of motion states that for every action there 
is an equal and opposite reaction. Comets expel dust and gas, 
usually from localized regions, on the sunward side of the 
nucleus. This action causes a reaction by the cometary nucleus, 
slightly speeding it up or slowing it down. Such effects are 
called Rnon-gravitational forcesS and are simply rocket effects, 
as if someone had set up one or more rocket motors on the nucleus. 
In general both the size and shape of a cometUs orbit are changed 
by the non-gravitational forces -- not by much but by enough to 
totally confound all of the celestial mechanics experts of the 
19th and early 20th centuries. Comet Halley arrived at its point 
closest to the Sun (perihelion) in 1910 more than three days late, 
according to the best predictions. Only after F. L. Whipple 
published his icy conglomerate model of a degassing nucleus in 
1950 did it all begin to make sense. The predictions for the time 
of perihelion passage of Comet Halley in 1986, which took into 
account a crude model for the reaction forces, were off by less 
than fiveJhours.
 
Much of modern physics is expressed in terms of conservation laws, 
laws about quantities which do not change for a given system. 
Conservation of energy is one of these laws, and it says that 
energy may change form, but it cannot be created or destroyed. 
Thus the energy of motion (kinetic energy) of Shoemaker-LevyJ9 
will be changed largely to thermal energy when the comet is halted 
by JupiterUs atmosphere and destroyed in the process. When one 
body moves about another in the vacuum of space, the total energy 
(kinetic energy plus potential energy) is conserved.
 
Another quantity that is conserved is called angular momentum. In 
the first paragraph of this section, it was stated that the 
geometric constants of an ellipse are its semimajor axis and 
eccentricity. The dynamical constants of a body moving about 
another are energy and angular momentum. The total (binding) 
energy is inversely proportional to the semimajor axis. If the 
energy goes to zero, the semimajor axis becomes infinite and the 
body escapes. The angular momentum is proportional both to the 
eccentricity and the energy in a more complicated way, but, for a 
given energy, the larger the angular momentum the more elongated 
the orbit.
 
The laws of motion do not require that bodies move in circles (or 
even ellipses for that matter), but if they have some binding 
energy, they must move in ellipses (not counting perturbations by 
other bodies), and it is then the angular momentum which 
determines how elongated is the ellipse. Comets simply are bodies 
which in general have more angular momentum per unit mass than do 
planets and therefore move in more elongated orbits. Sometimes the 
orbits are so elongated that, because we can observe only a small 
part of them, they cannot be distinguished from a parabola, which 
is an orbit with an eccentricity of exactly one. In very general 
terms, one can say that the energy determines the size of the 
orbit and the angular momentum the shape.
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
3. The Fragmentation of Comets
 
		Every body is held together by two forces, its self-
gravitation and its internal strength due to molecular bonding. 
With no external forces on it (and no initial rotation) a liquid 
body would form a perfect sphere just from self-gravitation (and 
from very weak molecular forces -- surface tension). Approaching 
another body, the sphere would begin to elongate toward that body. 
Finally, when the difference in gravitational force on the near 
side and far side of the former sphere exceeded the self-
gravitation, the body would be torn apart. The distance from the 
larger body at which this disruption occurs is the so-called Roche 
limit, named for the man who first studied the problem. The 
differential gravitational effects of the Moon and the Sun are 
what raise the tides in EarthUs oceans, and such forces are often 
referred to as tidal forces.
 
Solid bodies have intrinsic strength due to their molecular bonds. 
Aluminum wire may have a tensile strength of 2.4J4 109Jdynes/cm2 
(5JmillionJlb./ft.2) and good steel wire a tensile strength 
10Jtimes larger still, which far exceeds the tidal force of 
anything short of a black hole. As stated in Section 1, comets 
have very low tensile strength, near 1J4J103Jdynes/cm2 
(2Jlb./ft.2). They can be pulled apart very easily by tidal force 
(or any other substantial force, for that matter). Some 25 comets 
have been observed to split over the past two centuries. In other 
cases two or more comets have been discovered in nearly the same 
orbit, and calculations have indicated that they were once a 
single comet. A few of these cases have been obviously 
attributable to the tidal forces of Jupiter (Comet BrooksJ2 and 
Comet Shoemaker-LevyJ9) or the Sun (the Kreutz comet family), 
while other splittings have to be attributed to less obvious 
causes. For example, the loss of material from an active comet, 
which tends to occur from a few localized areas, is bound to 
weaken it. It may be that a rapidly rotating comet can be weakened 
to the point where the centrifugal force is sufficient to cause 
large pieces to break off.J
 
The Kreutz family is the name given to many comets which closely 
approach the Sun from one direction in space. They always approach 
the Sun to within 3JmillionJkm or less, and some have actually hit 
the Sun. The family was named for Heinrich Kreutz who published 
extensive monographs on three of these comets and supported the 
idea that they had a common origin, perhaps in a giant comet 
observed in 372JB.C. Today the Kreutz family has eight definite, 
well-studied members; 16Jprobable members (that are listed as 
probable only because they didnUt survive passage within 
800,000Jkm of the Sun to permit further study); and three more 
possible members. Extensive work by Brian Marsden suggests that 
all of these may have resulted from the splitting of two comets 
around 1100JA.D., which in turn may have been the parts of the 
great comet of 372JB.C. Those Kreutz fragments which survive their 
encounters with the Sun are often found to have split yet again! 
 
The classic Roche limit for a (fluid) body of density 1Jg/cm3 
approaching Jupiter is about 119,000Jkm above the cloud tops of 
the planet. It is about 169,000Jkm for a body having a density of 
0.5Jg/cm3. More complete modern theories making different 
assumptions result in a somewhat smaller limit. In 1886 Comet 
BrooksJ2 came within 72,000Jkm of JupiterUs clouds and split into 
two pieces. In July 1992 Comet Shoemaker-LevyJ9 came within about 
25,000Jkm of JupiterUs clouds and fragmented into 21Jor more large 
pieces and an enormous amount of smaller debris down to micron or 
submicron size. Details of this last event follow.
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
4. The Discovery and Early Study of Shoemaker-Levy 9
 
		Comet Shoemaker-LevyJ9 was discovered photographically 
by the husband and wife scientific team of Carolyn S. and Eugene 
M. Shoemaker and David H. Levy on MarchJ24, 1993, using the 0.46-m 
(18-in.) Schmidt telescope at Palomar Observatory in California. 
Its discovery was a serendipitous product of their continuing 
search for Rnear-Earth objects,S and the R9S indicates that it was 
the ninth short-period comet (period less than 200Jyears) 
discovered by this team. Near-Earth objects are bodies whose 
orbits come nearer to the Sun than that of Earth and hence have 
some potential for collisions with Earth. The appearance of the 
comet was reported as Rmost unusualS; the object appeared as Ra 
dense, linear bar about 1JarcJminute longS and had a Rfainter, 
wispy Ttail.U S (A circle is divided into 360 degrees, each degree 
into 60Jminutes, and each minute into 60Jseconds. The word RarcS 
is added to denote an angular measure rather than time. The 
diameter of the Moon is near 30JarcJminutes, for example, while 
the apparent diameter of Jupiter when closest to Earth is 
50JarcJseconds.) The cometUs brightness was reported as about 
magnitudeJ14, more than a thousand times too faint to be seen with 
the naked eye.
 
The existence of this object was soon confirmed by James V. Scotti 
of the Spacewatch program at the University of Arizona, and the 
International Astronomical UnionUs Central Bureau for Astronomical 
Telegrams immediately issued RCircular No. 5725S reporting the 
discovery as a new comet, giving it the provisional designation of 
1993e (the fifth comet discovered or recovered in 1993). Scotti 
reported at least five condensations in a Rlong, narrow train 
about 47JarcJseconds in length and about 11JarcJseconds in width,S 
with dust trails extending 4.20JarcJminutes to the east and 
6.89JarcJminutes to the west and tails extending about 
1JarcJminute from elements of the nuclear train. Bureau director 
Brian G. Marsden noted that the comet was some 4< from Jupiter and 
that its motion suggested that it could be near JupiterUs distance 
from the Sun. 
 
By March 27 Marsden had enough positions to attempt to derive 
possible orbits. One elliptical solution gave a close approach to 
Jupiter in July 1992. Also on March 27, Jane Luu and David Jewitt 
took an image with the 2.2-m telescope on Mauna Kea in Hawaii that 
showed as many as 17Jseparate sub-nuclei Rstrung out like pearls 
on a stringS 50JarcJseconds long, and this was reported in 
Circular No. 5730 two days later. FigureJ4 shows an early image 
taken by Scotti on MarchJ30, 1993. This long exposure (440 seconds 
on a CCD detector) brings out the faint detail of the debris 
field, though it overexposes the individual nucleus fragments. 
FigureJ5 is an image from the Hubble Space Telescope (HST), taken 
by Harold A. Weaver and collaborators on July 1, 1993 (before the 
HST repair mission), that clearly shows at least 15Jindividual 
fragments in one image frame of the train.
 
In IAU Circular No. 5744, dated AprilJ3, 1993, Marsden used 
positions covering a period of 17Jdays (including two prediscovery 
positions from MarchJ15) and was able to report that no orbit of 
very long period (near parabolic) was possible. The orbit had to 
be an ellipse of rather small eccentricity relative to the Sun and 
relatively short period. Since it was not at all obvious where the 
center of mass of this new comet lay, most observers were just 
reporting the position of what appeared to be the center of the 
train. This made an accurate orbit (or orbits) difficult to 
determine. Marsden suggested that a very close approach to Jupiter 
in 1992 continued to be a distinct possibility, and the orbit he 
chose to publish was one with the comet Rat least temporarilyS in 
orbit around Jupiter.
 
By May 22 Marsden had almost 200 positions of the center of the 
train. In Circular No. 5800 he reported on an orbit computed 
MayJ18 by Syuichi Nakano that showed the comet approaching within 
120,000Jkm of Jupiter on JulyJ8, 1992, and approaching again, this 
time within 45,000Jkm of the center of Jupiter, on JulyJ25, 1994. 
Marsden noted that this distance was less than the radius of 
Jupiter. In other words, the comet, or at least parts of it, could 
very well hit Jupiter.
 
By October 18, 1993, Paul W. Chodas and DonaldJK. Yeomans were 
able to report at the annual American Astronomical SocietyUs 
Division of Planetary Sciences meeting that the probability of 
impact for the major fragments of Shoemaker-LevyJ9 was greater 
than 99%. The fragments apparently would hit over a period of 
several days, centered on JulyJ21.2, on the night side of Jupiter 
at latitude 44!JS and longitude 35! past the midnight meridian, 
according to available observations. This unfortunately is also 
the back side of Jupiter as viewed from Earth. The 1992 approach 
to Jupiter that disrupted the comet was calculated to have been at 
a distance of 113,000Jkm from the planetUs center and only 
42,000Jkm above its cloud tops. Furthermore, they found that the 
comet had been in a rapidly changing orbit around Jupiter for some 
time before this, probably for at least several decades. It did 
not fragment during earlier approaches to Jupiter, however, 
because these were at much greater distances than that of 1992. 
 
After recovery of the comet on DecemberJ9, following the period 
during which it was too near to the Sun in the sky to observe, 
Chodas and Yeomans found that the probability was greater than 
99.99% that all the large fragments will hit Jupiter. The 
encounter period is now centered on JulyJ19.5, and orbits for 
individual fragments are uncertain by about 0.03Jdays (1Js). The 
impact site has moved closer to the limb of Jupiter, now near 75! 
from the midnight meridian and only a few degrees beyond the dark 
limb as seen from Earth, but all pieces still impact on the back 
side. The 1992 approach that split the comet is now calculated to 
have occurred on JulyJ7.84 and only 25,000Jkm (15,500Jmi.) above 
the clouds. These data now cover a much longer time base and are 
based upon calculations for individual fragments. They are 
unlikely to change significantly in the future. The comet probably 
approached Jupiter no nearer than about 9JmillionJkm in the orbit 
prior to that of 1992.
 
In a comprehensive paper prepared for The Astronomical Journal, 
Zdenek Sekanina, Chodas, and Yeomans report on the details of the 
breakup of Shoemaker-LevyJ9 as calculated from the positions, 
motions, and brightness of the fragments and debris. They used 
data from Jewitt, Luu, and Chen taken in Hawaii, Scotti in 
Arizona, and WeaverUs Hubble Space Telescope (HST) observing team. 
For example, the 11 brightest fragments as measured with the HST, 
visual (V) magnitude 23.7-24.8 or about 15JmillionJtimes too faint 
to be seen by the naked eye, had the brightness one would expect 
from spheres 4.3Jdown to 2.5Jkm in diameter, assuming a normal 
cometary reflectivity for the fragments (about 4%). Of course the 
fragments are not spheres, since tidal disruption tends to occur 
in planes perpendicular to the direction of the object causing the 
disruption (Jupiter) and since comets generally are not spherical 
to begin with. Nevertheless, adding up the sizes of these 
11Jfragments, the other fragments not precisely measured, and all 
of the debris making up the trails and tails, suggests that the 
original comet must have been at least 9Jkm in average diameter, 
and it could have been somewhat larger. This was a good-sized 
comet, about the same size as Comet Halley.
 
When comets split, the pieces do not go flying apart at a high 
velocity, each to immediately go into its own independent orbit. 
The escape velocity from a non-rotating spherical comet 5Jkm in 
radius with a density of 0.5Jg/cm3 (half that of water) is 
2.65Jm/s (6.5Jmph). If suddenly freed of gravity and molecular 
bonds, a particle at the equator of that 10-km body, assuming a 
rotation period of 12Jhours, would depart with a velocity of only 
0.72 m/s (1.6 mph) relative to the center of the comet. Some 
comets appear to rotate more rapidly than once per half day, while 
many, such as Halley, rotate more slowly. In any case the 
centrifugal force on unattached pieces of material lying on the 
surface of a rotating comet is not normally sufficient to overcome 
the gravity holding them there. Pieces do not fly off of the 
nucleus Rspontaneously.S Even when the tidal forces overcome self-
gravity the pieces separate slowly, and they continue to interact 
gravitationally. More important, the pieces bang into one another, 
changing their velocities and perhaps fragmenting further. 
 
In the case of Shoemaker-LevyJ9, Sekanina, Chodas, and Yeomans 
estimate that although fragmentation probably began before closest 
approach to Jupiter, dynamic independence of the pieces didnUt 
occur until almost twoJhours after closest approach. For a peahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
5. The Planet Jupiter
 
		Jupiter is the largest of the nine planets, more than 
10Jtimes the diameter of Earth and more than 300Jtimes its mass. 
In fact the mass of Jupiter is almost 2.5Jtimes that of all the 
other planets combined. Being composed largely of the light 
elements hydrogen and helium, its mean density is only 1.314Jtimes 
that of water. The mean density of Earth is 5.245Jtimes that of 
water. The pull of gravity on Jupiter at the top of the clouds at 
the equator is 2.4Jtimes as great as gravityUs pull at the surface 
of Earth at the equator. The bulk of Jupiter rotates once in 9h 
55.5m, although the period determined by watching cloud features 
differs by up to fiveJminutes due to intrinsic cloud motions.
 
The visible RsurfaceS of Jupiter is a deck of clouds of ammonia 
crystals, the tops of which occur at a level where the pressure is 
about half that at EarthUs surface. The bulk of the atmosphere is 
made up of 89% molecular hydrogen (H2) and 11% helium (He). There 
are small amounts of gaseous ammonia (NH3), methane (CH4), water 
(H2O), ethane (C2H6), acetylene (C2H2), carbon monoxide (CO), 
hydrogen cyanide (HCN), and even more exotic compounds such as 
phosphine (PH3) and germane (GeH4). At levels below the deck of 
ammonia clouds there are believed to be ammonium hydro-sulfide 
(NH4SH) clouds and water crystal (H2O) clouds, followed by clouds 
of liquid water. The visible clouds of Jupiter are very colorful. 
The cause of these colors is not yet known. RContaminationS by 
various polymers of sulfur (S3, S4, S5, and S8), which are yellow, 
red, and brown, has been suggested as a possible cause of the riot 
of color, but in fact sulfur has not yet been detected 
spectroscopically, and there are many other candidates as the 
source of the coloring.
 
The meteorology of Jupiter is very complex and not well 
understood. Even in small telescopes, a series of parallel light 
bands called zones and darker bands called belts is quite obvious. 
The polar regions of the planet are dark. (See FigureJ7.) Also 
present are light and dark ovals, the most famous of these being 
Rthe Great Red Spot.S The Great Red Spot is larger than Earth, and 
although its color has brightened and faded, the spot has 
persisted for at least 162.5Jyears, the earliest definite drawing 
of it being SchwabeUs of Sept.J5, 1831. (There is less positive 
evidence that Hooke observed it as early as 1664.) It is thought 
that the brighter zones are cloud-covered regions of upward moving 
atmosphere, while the belts are the regions of descending gases, 
the circulation driven by interior heat. The spots are thought to 
be large-scale vortices, much larger and far more permanent than 
any terrestrial weather system.
 
The interior of Jupiter is totally unlike that of Earth. Earth has 
a solid crust RfloatingS on a denser mantle that is fluid on top 
and solid beneath, underlain by a fluid outer core that extends 
out to about half of EarthUs radius and a solid inner core of 
about 1,220-km radius. The core is probably 75% iron, with the 
remainder nickel, perhaps silicon, and many different metals in 
small amounts. Jupiter on the other hand may well be fluid 
throughout, although it could have a RsmallS solid core (say up to 
15Jtimes the mass of Earth!) of heavier elements such as iron and 
silicon extending out to perhaps 15% of its radius. The bulk of 
Jupiter is fluid hydrogen in two forms or phases, liquid molecular 
hydrogen on top and liquid metallic hydrogen below; the latter 
phase exists where the pressure is high enough, say 3-4 million 
atmospheres. There could be a small layer of liquid helium below 
the hydrogen, separated out gravitationally, and there is clearly 
some helium mixed in with the hydrogen. The hydrogen is convecting 
heat (transporting heat by mass motion) from the interior, and 
that heat is easily detected by infrared measurements, since 
Jupiter radiates twice as much heat as it receives from the Sun. 
The heat is generated largely by gravitational contraction and 
perhaps by gravitational separation of helium and other heavier 
elements from hydrogen, in other words, by the conversion of 
gravitational potential energy to thermal energy. The moving 
metallic hydrogen in the interior is believed to be the source of 
JupiterUs strong magnetic field.
 
JupiterUs magnetic field is much stronger than that of Earth. It 
is tipped about 11! to JupiterUs axis of rotation, similar to 
EarthUs, but it is also offset from the center of Jupiter by about 
10,000Jkm (6,200Jmi.). The magnetosphere of charged particles 
which it affects extends from 3.5Jmillion to 7JmillionJkm in the 
direction toward the Sun, depending upon solar wind conditions, 
and at least 10Jtimes that far in the anti-Sun direction. The 
plasma trapped in this rotating, wobbling magnetosphere emits 
radio frequency radiation measurable from Earth at wavelengths 
from 1Jm or less to as much as 30Jkm. The shorter waves are more 
or less continuously emitted, while at longer wavelengths the 
radiation is quite sporadic. Scientists will carefully monitor the 
Jovian magnetosphere to note the effect of the intrusion of large 
amounts of cometary dust into the Jovian magnetosphere.
 
The two Voyager spacecraft discovered that Jupiter has faint dust 
rings extending out to about 53,000Jkm above the atmosphere. The 
brightest ring is the outermost, having only about 800-km width. 
Next inside comes a fainter ring about 5,000Jkm wide, while very 
tenuous dust extends down to the atmosphere. Again, the effects of 
the intrusion of the dust from Shoemaker-LevyJ9 will be 
interesting to see, though not easy to study from the ground.
 
The innermost of the four large satellites of Jupiter, Io, has 
numerous large volcanos that emit sulfur and sulfur dioxide. Most 
of the material emitted falls back onto the surface, but a small 
part of it escapes the satellite. In space this material is 
rapidly dissociated (broken into its atomic constituents) and 
ionized (stripped of one or more electrons). Once it becomes 
charged, the material is trapped by JupiterUs magnetic field and 
forms a torus (donut-shape) completely around Jupiter in IoUs 
orbit. Accompanying the volcanic sulfur and oxygen are many sodium 
ions (and perhaps some of the sulfur and oxygen as well) that have 
been sputtered (knocked off the surface) from Io by high energy 
electrons in JupiterUs magnetosphere. The torus also contains 
protons (ionized hydrogen) and electrons. It will be fascinating 
to see what the effects are when large amounts of fine 
particulates collide with the torus.
 
Altogether, Jupiter has 16 known satellites. The two innermost, 
Metis and Adrastea, are tiny bodies, having radii near 20Jand 
10Jkm respectively, that interact strongly with the rings and in 
fact may be the source of the rings. That is, the rings may be 
debris from impacts on the satellites. Amalthea and Thebe are 
still small, having mean radii of 86.2Jand about 50Jkm, 
respectively, but they are close to Jupiter and may serve as 
useful reflectors of light from some of the impacts. The Galilean 
satellites (the four moons discovered by Galileo in 1610), Io, 
Europa, Ganymede, and Callisto, range in radius from 1,565Jkm 
(Europa) to 2,634Jkm (Ganymede). (EarthUs Moon has a radius of 
1,738Jkm.) They lie at distances of 421,700Jkm (Io) to 
1,883,000Jkm (Callisto) from Jupiter. These objects will serve as 
the primary reflectors of light from the impacts for those 
attempting to indirectly observe the actual impacts. The outer 
eight satellites are all tiny (less than 100-km radius) and at 
large distances (greater than 11JmillionJkm) from Jupiter. They 
are expected to play no role in impact studies.
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
 
6. The Final Orbit of Shoemaker-Levy 9
 
		The motion of Comet Shoemaker-LevyJ9 can technically be 
described as chaotic, which means that calculations based upon the 
input of comet positions having very tiny differences (small input 
errors) causes large differences in the results of calculations of 
the subsequent motion and the apparent prior motion. Large 
perturbations caused by successive close approaches to Jupiter 
have resulted in each orbit being different in size, shape, and 
orientation. The orbits have not been the simple result of a small 
body in orbit around a large one but rather the product of a Rtug 
of warS between Jupiter and the Sun, a classic Rthree-body 
problem.S Near to Jupiter the planetUs gravity has dominated the 
motion, but far from Jupiter the Sun is more important. On 
JulyJ16, 1993, at apojove (the point farthest from Jupiter) in the 
current orbit, Shoemaker-LevyJ9 was almost 1,200Jtimes as far from 
Jupiter as at the time of breakup, a distance of 50JmillionJkm, 
equal to a third of the distance of Earth from the Sun. The comet 
has been in a closed orbit around Jupiter for many decades, but 
that orbit is far from stable. FigureJ8 by Chodas shows what this 
orbit will look like as viewed from the Sun at the time of impact. 
It is tipped (inclined) 53! to JupiterUs equator as measured at 
apojove and is bent about 20! more near to Jupiter. (A three-body 
orbit rarely lies in one plane like the simple two-body orbit.) 
 
During this final orbit, after breakup in July 1992, Shoemaker-
LevyJ9 was followed carefully from discovery in March 1993 until 
the time the cometUs angular distance from the Sun became too 
small to permit observations. The last useful astrometric 
(positional) observations reported before the fragments were lost 
in the glare of the Sun were made on JulyJ11. The comet was 
recovered (found again after almost fiveJmonths without 
observations) by Scotti and Tom Gehrels on DecemberJ9, with the 
comet rising above the horizon a bit more than threeJhours before 
the Sun in the morning sky. (The comet is so faint that it cannot 
be observed in twilight or too low on the horizon.) The quality of 
the predictions for the time of impact of the individual fragments 
on Jupiter will depend upon the number of high-quality astrometric 
observations of each comet fragment made between December 1993 and 
the time of impact. A week before the impacts the times should be 
known at least to 110Jminutes (with 50% confidence), improving to 
perhaps 15Jminutes a half day before impact.
 
At a fall planetary astronomy meeting (DPS) Jewitt, Luu, and Chen 
exhibited an image showing 21Jdistinct fragments in the Shoemaker-
LevyJ9 nucleus train. At discovery in March, this train was about 
50Jarc seconds or 162,000Jkm in length as projected on the sky. 
This angular distance had increased by about 40% (and the true 
linear distance by about 50%, since Jupiter was then farther from 
Earth) by the time the comet was lost in the glare of the Sun in 
July. The spreading is caused mainly by the fact that the piece 
closest to Jupiter at breakup was some 9Jkm closer than the 
farthest piece (the diameter of the comet) and therefore entered a 
faster orbit. The orbits are all so elongated that from Earth they 
appear to be nearly a straight line with the fragments strung out 
along it. The fragment nearest to Jupiter at breakup remains 
nearest to it and will be the first to impact. At this writing, 
Chodas and Yeomans predict that the train will reach an apparent 
length of some 1,286 arc seconds at the time the first of the 
fragments enters JupiterUs atmosphere. The true length of the 
train will be 4,900,000Jkm at that time, and it will require 
5.5Jdays for all of the major fragments to impact.
 
The new data taken following solar conjunction (the closest 
apparent approach to the Sun as projected against the sky) more 
than doubled the length of time since discovery for which cometary 
positions were available. With this new data, it appears that the 
impacts will be centered on about JulyJ19.5, a day and a half 
earlier than the first predictions. The approach to Jupiter that 
shattered the comet appears to have been even closer than first 
thought, about 96,000Jkm from the planetUs center and only 
25,000Jkm above the clouds. The revised orbit has also moved the 
impact points closer to the visible hemisphere, but unfortunately 
still on the back side as seen from Earth. The brightest fragment, 
of which there is some indication that it itself is fragmented, 
will impact on about JulyJ20.78 and contains about 10% of the 
total mass of the comet. The other 20Jobserved fragments contain 
more than 80% of the mass. The remaining mass is contained in all 
of the dust and small pieces in the train, the trails, and the 
tails. Most of this mass also will hit Jupiter over a period of 
several months beginning about JulyJ10, but it probably will cause 
few or no detectable effects.
 
Meanwhile, the dust trails of small debris will continue to 
spread, as will the major fragments. The east-northeast trail is 
expected to reach a maximum apparent length of some 70Jarc minutes 
in late June of 1994 and then decrease again in apparent length 
with the tip turning around into a RVS shape. The west-southwest 
trail may reach a length of almost 100Jarc minutes before impacts 
begin. Only the larger trail material will actually impact 
Jupiter. The earliest dust will begin to hit about JulyJ10, and 
impacts will continue into October. The smaller dust will be moved 
into the tail by solar radiation pressure and will miss the planet 
completely. 
 
If upon further study it is found that the pieces of Shoemaker-
LevyJ9 have continued to fragment, then predicting impact times 
will be much more difficult and the predictions less reliable. 
Such continued fragmentation of pieces already badly fractured is 
very possible, but fragmentation in the last day or two, when it 
is most likely to occur, will have no significant effect on the 
predicted times of impact. The pieces typically separate with a 
velocity of less than a meter per second. There are 86,400Jseconds 
in a day, so even pieces separating at a full meter per second 
would be only 86.4Jkm apart after one day. Moving jointly at a 
velocity which reaches 60Jkm/s at impact, the pieces would hit 
within a few seconds of each other. The effect of further 
splitting upon the impact phenomena would be far greater and is 
discussed in the next section.
 
Figure 9 by David Seal shows the final segment of the comet 
fragmentUs trajectories. They will impact near a latitude of 44{JS 
and a longitude 70{ past the midnight meridian, still 10{ beyond 
the limb of Jupiter as seen from Earth, impacting the atmosphere 
at an angle of about 42{ from vertical.
 
Observing conditions from Earth will not be ideal at the time of 
the impacts, since there will be only about twoJhours of good 
observing time for large telescopes at any given site after the 
sky gets good and dark and before Jupiter comes too close to the 
horizon to observe. At least it will be summer in the northern 
hemisphere, and there will be a better chance for good weather 
where many observatories are located. With 21Jpieces hitting over 
a 5.5-day period, there will be an impact on average about every 
6Jhours, so any given site should have about one chance in three 
of observing at the actual time of an impact each night. Since the 
impacts will be on the back side of Jupiter, light from the 
impacts can only be observed by reflection from JupiterUs moons or 
perhaps from the rings or the dust comae of the comet fragments. 
Those attempting observations of the effects of the impacts on 
Jupiter can begin about 20Jminutes after the impacts, when the 
impact area rotates into view from Earth.
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
7. The Collisions
 
		Exactly what will happen as the fragments of Shoemaker-
LevyJ9 enter the atmosphere of Jupiter is very uncertain, though 
there are many predictions. If the process were better understood, 
it would be less interesting. Certainly scientists have never 
observed anything like this event. There seems to be complete 
agreement only that the major fragments will hit Jupiter and that 
these collisions will occur on the back side of Jupiter as seen 
from Earth. 
 
Any body moving through an atmosphere is slowed by atmospheric 
drag, by having to push the molecules of that atmosphere out of 
the way. The kinetic energy lost by the body is given to the air 
molecules. They move a bit faster (become hotter) and in turn heat 
the moving body by conduction. This frictional process turns 
energy of mass motion (kinetic energy) into thermal energy 
(molecular motion). The drag increases roughly as the square of 
the velocity. In any medium a velocity is finally reached at which 
the atmospheric molecules can no longer move out of the way fast 
enough and they begin to pile up in front of the moving body. This 
is the speed of sound (MachJ1 -- 331.7Jm/s or 741Jmph in air on 
Earth at sea level). A discontinuity in velocity and pressure is 
created which is called a shock wave. Comet Shoemaker-LevyJ9 will 
enter JupiterUs atmosphere at about 60Jkm/s, which would be about 
180Jtimes the speed of sound on Earth (MachJ180!) and is about 
50Jtimes the speed of sound even in JupiterUs very light, largely 
hydrogen atmosphere. 
 
At high supersonic velocities (much greater than MachJ1) enough 
energy is transferred to an intruding body that it becomes 
incandescent and molecular bonds begin to break. The surface of 
the solid body becomes a liquid and then a gas. The gas atoms 
begin to lose electrons and become ions. This mixture of ions and 
electrons is called a plasma. The plasma absorbs radio waves and 
is responsible for the communication blackouts that occur when a 
spacecraft such as the Space Shuttle reenters EarthUs atmosphere. 
The atmospheric molecules are also dissociated and ionized and 
contribute to the plasma. At higher temperatures, energy transfer 
by radiation becomes more important than conduction. Ultimately 
the temperatures of the plasma and the surface of the intruding 
body are determined largely by the radiation balance. The 
temperature may rise to 50,000JK (90,000!JF) or more for very 
large bodies such as the fragments of Shoemaker-LevyJ9 entering 
JupiterUs atmosphere at 60Jkm/s. The loss of material as gas from 
the impacting body is called thermal ablation. The early manned 
spacecraft (Mercury, Gemini, and Apollo) had Rablative heat 
shieldsS made of a material having low heat conductivity (through 
to the spacecraft) and a high vaporization temperature (strong 
molecular bonds). As this material was lost, as designed, it 
carried away much of the orbital energy of the spacecraft 
reentering EarthUs atmosphere.
 
There are other forms of ablation besides thermal ablation, the 
most important being loss of solid material in pieces. In a comet, 
fragile to begin with and further weakened and/or fractured by 
thermal shock and by melting, such spallation of chips or chunks 
of material has to be expected. Turbulence in the flow of material 
streaming from the front of the shock wave can be expected to 
strip anything that is loose away from the comet and send it 
streaming back into the wake. The effect of increasing 
temperature, pressure, and vibration on an intrinsically weak body 
is to crush it and cause it to flatten and spread. Meanwhile the 
atmosphere is also increasing in density as the comet penetrates 
to lower altitudes. All of these processes occur at an ever 
increasing rate (mostly exponentially).
 
On Earth a sizable iron meteoroid or even some relatively low 
velocity stony meteoroids can survive all of this and impact the 
surface, where we collect them for study and exhibition. (Small 
bodies traveling in space are called meteoroids. The visible 
phenomena which occur as a meteoroid enters the atmosphere is 
called a meteor. Surviving solid fragments are called meteorites. 
There is no sharp size distinction between meteoroids and 
asteroids. Normally, if the body has been detected telescopically 
before entering the atmosphere, it has been called an asteroid.) 
Many meteoroids suffer what is called a Rterminal explosionS when 
crushed while still many kilometers above the ground. This is what 
happened in Tunguska, Siberia, in 1908. There a body with a mass 
of some 109Jkg (2.2JbillionJlb.) and probably 90Jto 190Jm in 
diameter entered EarthUs atmosphere at a low angle with a velocity 
of less than 15Jkm/s. It exploded at an altitude of perhaps 5-
10Jkm. This explosion, equivalent to 10-20Jmegatons of TNT, 
combined with the shock wave generated by the bodyUs passage 
through the atmosphere immediately before disruption, leveled some 
2,200Jkm2 of Siberian forest. The Tunguska body had a tensile 
strength of some 2J4J108Jdynes/cm2, more than 100,000Jtimes the 
strength of Shoemaker-LevyJ9, but no surviving solid fragments of 
it (meteorites) have ever been found. The fragile Shoemaker-LevyJ9 
fragments entering an atmosphere of virtually infinite depth at a 
much higher velocity will suffer almost immediate destruction. The 
only real question is whether each fragment may break into several 
pieces immediately after entry, and therefore exhibit multiple 
smaller explosions, or whether it will survive long enough to be 
crushed, flattened, and obliterated in one grand explosion and 
terminal fireball.
 
Scientists have differed in their computations of the depths to 
which fragments of given mass will penetrate JupiterUs atmosphere 
before being completely destroyed. If a Rterminal explosionS 
occurs above the clouds, which are thought to lie at a pressure 
level of about 0.5Jbar or roughly 0.5JEarth atmosphere (see 
SectionJ5), then the explosion will be very bright and easily 
observable by means of light reflected from JupiterUs satellites. 
Using ablation coefficients derived from observation of many 
terrestrial fireballs, Sekanina predicts that the explosions 
indeed will occur above the clouds. Mordecai-Mark Mac Low and 
Kevin Zahnle have made calculations using an astrophysical 
hydrodynamic code (ZEUS) on a supercomputer. They assume a fluid 
body as a reasonable approximation to a comet, since comets have 
so little strength, and they predict that the terminal explosions 
will occur near the 10-bar level, well below the clouds. Others 
have suggested still deeper penetration, but most calculations 
indicate that survival to extreme depths is most unlikely. The 
central questions then appear to be whether terrestrial experience 
with lesser events can be extrapolated to events of such magnitude 
and whether all the essential physics has been included in the 
supercomputer calculations. We can only wait and observe what 
really happens, letting nature teach us which predictions were 
correct.
 
O.K. So an explosion occurs at some depth. What does that do? What 
happens next? Sekanina calculates that about 93% of the mass of a 
1013-kg fragment remains one second before the terminal explosion 
and the velocity is still almost 60Jkm/s. During that last second 
the energy of perhaps 10,000 100-megaton bombs is released. Much 
of the cometary material will be heated to many tens of thousands 
of degrees, vaporized, and ionized along with a substantial amount 
of JupiterUs surrounding atmosphere. The resulting fireball should 
balloon upward, even fountaining clear out of the atmosphere, 
before falling back and spreading out into JupiterUs atmosphere, 
imitating in a non-nuclear fashion some of the atmospheric 
hydrogen bomb tests of the 1950s. Once again, the total energy 
release here will be many thousands of times that of any hydrogen 
bomb ever tested, but the energy will be deposited initially into 
a much greater volume of JupiterUs atmosphere, so the energy 
density will not be so high as in a bomb, and, of course, there 
will be no gamma rays or neutrons (nuclear radiation or particles) 
flying about. The energy of these impacts will be beyond any prior 
experience. The details of what actually occurs will be determined 
by the observations in July 1994, if the observations are 
successful. 
 
If differential gravitation (tidal forces) should further fragment 
a piece of the comet, say an hour or two before impact, the pieces 
can be expected to hit within a second of each other. In one 
second a point at 44! latitude on Jupiter will rotate 9Jkm 
(5.6Jmi.), however, so the pieces would enter the atmosphere some 
distance apart. Smaller pieces will explode at higher altitudes 
but not so spectacularly. If smaller pieces do explode above the 
clouds, they may be more RvisibleS than larger pieces exploding 
below the clouds. It is also possible that implanting somewhat 
less energy density over a wider volume of atmosphere might create 
a more visible change in JupiterUs atmosphere. Sekanina notes that 
pieces smaller than about 1.3-km mean radius should not be further 
fragmented by tidal forces unless they were already weakened by 
earlier events.
 
One of the more difficult questions to answer is just how bright 
these events will be. Terrestrial fireballs have typically 
exhibited perhaps 1% luminous efficiency. In other words about 1% 
of the total kinetic energy has been converted to visible light. 
The greater magnitude of the Jupiter impacts may result in more 
energy appearing as light, but letUs assume the 1% efficiency. 
Then Sekanina calculates that a 1013-kg fragment, a reasonable 
value for the largest piece, will reach an apparent visual 
magnitude of -10 during the terminal explosion. This is 
1,000Jtimes JupiterUs normal 
brilliance and only 10Jtimes fainter than the full moon! Sekanina, 
of course, calculates that the explosions will occur above the 
clouds. And, remember that, unfortunately, these impacts will 
occur on JupiterUs back side as seen from Earth. There will be no 
immediate visible effect on the appearance of Jupiter. The light 
of the explosion may be seen reflected from the Galilean 
satellites of Jupiter, if they are properly placed at the times of 
impacts. Ganymede, for example, might brighten as much as six 
times, while Io could brighten to 35Jtimes its normal brilliance 
for a second before fading slowly, if the explosions occur above 
the clouds. This would certainly be visible in an amateur 
telescope and could conceivably be visible to the naked eye at a 
dark mountain site as a tiny flash next to Jupiter at the location 
of the normally invisible satellite. Emphasis on RtinyS! The 
brightness of explosions occurring below the clouds will be 
attenuated by a factor of at least 10,000, making them most 
difficult to observe. In the best of cases, these events will be 
spectacles for the mind to imagine and big telescopes to observe, 
not a free fireworks display.
 
The most recent predictions are that at least some of the impacts 
will occur very close to the planetary limb, the edge of the 
planetUs disk as seen from Earth. That edge still has 11! to 
rotate before it comes into sunlight. This means that the tops of 
some of the plumes associated with the rising fireballs may be 
just visible, although with a maximum predicted height of 3,000Jkm 
(0.8Jarc second as projected on the sky) they will be just 
RpeekingS over the limb. The newly repaired Hubble Space Telescope 
(HST), with its high resolution and low scattered light, may offer 
the best chance to see such plumes. By the time they reach their 
maximum altitude the plumes will be transparent (optically thin) 
and not nearly so bright as they were near the clouds. Some means 
of blocking out the bright light from Jupiter itself may be 
required in order to observe anything. A number of observers plan 
to look for evidence of plumes and to attempt to measure their 
size and brightness.
 
It also is difficult to predict the effects of the impacts on 
JupiterUs atmosphere. Robert West points out that a substantial 
amount of material will be deposited even in the stratosphere of 
Jupiter, the part of the atmosphere above the visible clouds where 
solar heating stabilizes the atmosphere against convection 
(vertical motion). Part of this material will come directly from 
small cometary grains, which vaporize during entry and recondense 
just as do meteoritic grains in the terrestrial atmosphere. Part 
will come from volatiles (ammonia, water, hydrogen sulfide, etc.) 
welling up from the deeper atmosphere as a part of the hot buoyant 
fireballs created at the time of the large impact events. Many 
millimeter-sized or larger pieces from the original breakup will 
also impact at various times for months and over the entire globe 
of Jupiter. There is relatively little mass in these smaller 
pieces, but it might be sufficient to create a haze in the 
stratosphere.
 
James Friedson notes that the fireball created by the terminal 
explosion will expand and balloon upward and perhaps spew 
vaporized comet material and JupiterUs entrained atmospheric gas 
to very high altitudes. The fireball may carry with it atmospheric 
gases that are normally to be found only far below JupiterUs 
visible clouds. Hence the impacts may give astronomers an 
opportunity to detect gases which have been hitherto hidden from 
view. As the gaseous fireball rises and expands it will cool, with 
some of the gases it contains condensing into liquid droplets or 
small solid particles. If a sufficiently large number of particles 
form, then the clouds they produce may be visible from Earth-based 
telescopes after the impact regions rotate onto the visible side 
of the planet. These clouds may provide the clearest indication of 
the impact locations after each event.
 
After the particles condense, they will grow in size by colliding 
and sticking together to form larger particles, eventually 
becoming sufficiently large to RrainS out of the visible part of 
the atmosphere. The length of time spent by the cloud particles at 
altitudes where they can be seen will depend principally on their 
average size; relatively large particles would be visible only for 
a few hours after an impact, while small particles could remain 
visible for several months. Unfortunately, it is very difficult to 
predict what the number and average size of the particles will be. 
A cloud of particles suspended in the atmosphere for many days may 
significantly affect the temperature in its vicinity by changing 
the amount of sunlight that is absorbed in the area. Such a 
temperature change could be observed from Earth by searching for 
changes in the level of JupiterUs emitted infrared light.
 
Glenn Orton notes that large regular fluctuations of atmospheric 
temperature and pressure will be created by the shock front of 
each entering fragment, somewhat analogous to the ripples created 
when a pebble is tossed into a pond, and will travel outward from 
the impact sites. These may be observable near layers of condensed 
clouds in the same way that regular cloud patterns are seen on the 
leeward side of mountains. JupiterUs atmosphere will be 
sequentially raised and lowered, creating a pattern of alternating 
cloudy areas where ammonia gas freezes into particles (the same 
way that water condenses into cloud droplets in our own 
atmosphere) and clear areas where the ice particles warm up and 
evaporate back into the gas phase. If such waves are detected, 
measurement of their wavelength and speed will 
allow scientists to determine certain important physical 
properties of JupiterUs deep atmospheric structure that are very 
difficult to measure in any other way. 
 
Whether or not RwaveS clouds appear, the ripples spreading from 
the impact sites will produce a wave structure in the temperature 
at a given level that may be observable in infrared images. In 
addition there should be compression waves, alternate compression 
and rarefaction in the atmospheric pressure, which could reflect 
from and refract within the deeper atmosphere, much as seismic 
waves reflect and refract due to density changes inside Earth. 
Orton suggests that these waves might be detected Rbreaking upS in 
the shallow atmosphere on the opposite side of the planet from the 
impacts. Others suggest the possibility of measuring the small 
temperature fluctuations wherever the waves surface, but this 
requires the ability to map fluctuations in JupiterUs visible 
atmosphere of a few millikelvin (a few thousandths of a degree). 
Detection of any of these waves will require a very fine infrared 
array detector (a thermal infrared camera).
 
Between the water and other condensable gases (volatiles) brought 
with the comet fragments and those exhumed by the rising 
fireballs, it is fairly certain that a cloud of condensed material 
will form at the location of the impacts themselves, at high 
altitudes where such gases seldom, if ever, exist in the usual 
course of things. It may be difficult to differentiate between the 
color or brightness of these condensates and any bright material 
below them in spectra at most visible wavelengths. However, at 
wavelengths where gaseous methane and hydrogen absorb sunlight, a 
distinction can easily be made between particles higher and lower 
in the atmosphere, because the higher particles will reflect 
sunlight better. Much of the light is absorbed before reaching the 
lower particles. Observing these clouds in gaseous absorption 
bands will then tell us how high they lie in the atmosphere, and 
observations over a period of time will indicate how fast high-
altitude winds are pushing them. The speed with which these clouds 
disappear will be a measure of particle sizes in the clouds, since 
large particles settle out much faster than small ones, hours as 
compared to days or months.
 
Orton also notes that in the presence of a natural wind shear (a 
region with winds having different speeds and/or directions) such 
as exists commonly across the face of Jupiter, a long-lived 
cyclonic feature can be created which is actually quite stable. It 
may gain stability by being fed energy from the wind shear, in 
much the same way that the Great Red Spot and other Jovian 
vortices are thought to be stabilized. Such creation of new, 
large, fixed RstormS systems is somewhat controversial, but this 
is a most intriguing possibility!
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
8. How Can These Impacts and Their Consequences be Studied?
 
Space-Based	
		There are at least four spacecraft -- Galileo, Ulysses, 
VoyagerJ2, and Clementine -- with some potential to observe the 
Jovian impacts from different vantage points than that of Earth. 
There is also the Hubble Space Telescope (HST), in orbit around 
Earth, which will view the event with essentially the same 
geometry as any Earth-based telescope. HST, however, has the 
advantages of perfect RseeingS (no atmospheric turbulence), very 
low scattered light, ultraviolet sensitivity, and the ability to 
observe much more than twoJhours each day. HST is scheduled to 
devote considerable time to the observation of Shoemaker-LevyJ9 
before as well as during the impacts.
 
The Galileo spacecraft has the best vantage point from which to 
observe the impacts. It is on its way to Jupiter and will be only 
246JmillionJkm away from the planet, less than a third the 
distance of Earth from Jupiter at that time. All of the impacts 
will occur directly in the field of view of its high resolution 
camera and 20!-25! of Jovian longitude from the limb. Images of 
Jupiter will be 60Jpicture elements (pixels) across, although the 
impact site will still be smaller than the resolution of the 
camera. Several instruments besides the camera have potential use, 
including an ultraviolet spectrometer, a near infrared mapping 
spectrometer, and a photopolarimeter radiometer. This last suite 
of instruments could acquire light curves (plots of intensity 
versus time) of the entry and fireball at many wavelengths from 
ultraviolet to thermal infrared (from wavelengths much shorter 
than visible light to much longer).
 
Using Galileo to make these observations will be challenging. The 
amount of data the spacecraft can transmit back to Earth is 
limited by the capability of its low-gain antenna and the time 
available on the receiving antennas of the National Aeronautics 
and Space AdministrationUs (NASAUs) Deep Space Network here on 
Earth. The RcommandsS that tell the spacecraft what to do must be 
sent up several weeks before the fact and before the impact times 
are known to better than about 20Jminutes with 95% certainty. A 
later command that simply triggers the entire command sequence may 
be possible. A lot of data frames can be stored in the Galileo 
tape recorder, but only about 5% of them can be transmitted back 
to Earth, so the trick will be to decide which 5% of the data are 
likely to include the impacts and to have the greatest scientific 
value, without being able to look at any of them first! After the 
fact, the impact times should be known quite accurately. This 
knowledge can help to make the decisions about which data to 
return to Earth.
 
The Ulysses spacecraft was designed for solar study and used a 
gravity assist from flying close to Jupiter to change its 
inclination (the tilt of its path relative to the plane of the 
planets) so it can fly over the poles of the Sun. In July 1994 it 
will be about 378JmillionJkm south of the plane of the planets 
(the ecliptic) and able to RlookS over the south pole of Jupiter 
directly at the impact sites. Unfortunately, Ulysses has no camera 
as a part of its instrument complement. It does have an extremely 
sensitive receiver of radio frequency signals from 1Jto 1000JkHz 
(kilohertz, or kilocycles in older terminology) called URAP 
(Unified Radio and Plasma wave experiment). URAP may be able to 
detect thermal radiation from the impact fireballs once they rise 
sufficiently high above interference from the Jovian ionosphere 
(upper atmosphere) and to measure a precise time history of their 
rapid cooling.
 
The Voyager 2 spacecraft is now far beyond Neptune (its last 
object of study back in 1989 after visiting Jupiter in 1979, 
Saturn in 1981, and Uranus in 1986) and is about 6.4JbillionJkm 
from the Sun. It can look directly back at the dark side of 
Jupiter, but the whole of Jupiter is now only two picture elements 
in diameter as seen by its high-resolution camera, if that 
instrument were to be used. In fact the camera has been shut down 
for several years, and the engineers who knew how to control it 
have new jobs or are retired. It would be very expensive to take 
the camera Rout of mothballsS and probably of limited scientific 
value. Voyager does have an ultraviolet spectrometer which is 
still taking data, and it will probably be used to acquire 
ultraviolet light curves (brightness versus time) of the impact 
phenomena. The possibility of using one or two other instruments 
is being considered, though useful results from them seem less 
likely.
 
A new small spacecraft called Clementine was launched on 
JanuaryJ25 of this year, intended to orbit the Moon and then 
proceed on to study the asteroid Geographos. Clementine has good 
imaging capabilities, but its viewpoint will not be much different 
from EarthUs. The impact sites will still be just over the limb, 
and ClementineUs resolution will be only a few picture elements on 
Jupiter. Since the spacecraft will be in cruise mode at the time, 
on its way to Geographos and not terribly busy, it seems probable 
that attempts will be made to observe RblipsS of light on the limb 
of Jupiter, from the entering fragments or the fireballs or 
perhaps light scattered from cometary material (coma) that has not 
yet entered the atmosphere. Useful light curves could result.
 
 
 
Ground-Based
		Many large telescopes will be available on Earth with 
which to observe the phenomena associated with the Shoemaker-
LevyJ9 impacts on Jupiter in visible, infrared, and radio 
wavelengths. Small portable telescopes can fill in gaps in 
existing observatory locations for some purposes. Imaging, 
photometry, spectroscopy, and radiometry will certainly be carried 
out using a multitude of detectors. Many of these attempts will 
fail, but some should succeed.
 
Apart from the obvious difficulty that the impacts will occur on 
the back side of Jupiter as seen from Earth, the biggest problem 
is that Jupiter in July can only be observed usefully for about 
twoJhours per night from any given site. Earlier the sky is still 
too bright and later the planet is too close to the horizon. 
Therefore, to keep Jupiter under continuous surveillance would 
require a dozen observatories equally spaced in longitude clear 
around the globe. A dozen observatories is feasible, but equal 
spacing is not. There will be gaps in the coverage, notably in the 
Pacific Ocean, where Mauna Kea, Hawaii, is the only astronomical 
bastion.
 
Measuring the light curve of the entering fragments and the post-
explosion fireball can be done only by measuring the light 
reflected from something else, one of JupiterUs satellites or 
perhaps the dust coma accompanying the fragment. That dust coma 
could still be fairly dense out to distances of 10,000Jkm or more 
around each fragment. Moving at 60Jkm/s, it will be almost 
threeJminutes before all of the dust also impacts Jupiter. Proper 
interpretation of such observations will be difficult, however, 
because the area of the Rreflector,S the coma dust particles, will 
be changing as the observations are made. Another complication is 
the brightness of Jupiter itself, which will have to be masked to 
the greatest extent possible. Observations in visible light 
reflected from the satellites will be relatively straightforward 
and can be done with small telescopes and simple photometers or 
imaging devices. This equipment is small enough that it can be 
transported to appropriate sites.
 
Spectroscopy of the entry phenomena via reflected light from one 
of the Galilean satellites could be used to determine the 
composition of the comet and the physical conditions in the 
fireball, if the terminal explosions occur above JupiterUs clouds. 
If the explosion occurs below the clouds, there will be too little 
light to do useful spectroscopy with even the largest telescopes.
 
The impact zone on Jupiter will rotate into sight from Earth about 
20Jminutes after each impact, though quite foreshortened as 
initially viewed. Extensive studies of the zone and the area 
around it can be made at that time. Such studies surely will 
include imaging, infrared temperature measurements, and 
spectroscopy using many of the largest telescopes on Earth. These 
studies will continue for some weeks, if there is any evidence of 
changes in JupiterUs atmosphere and cloud structure as a result of 
the impacts.
 
For example, astronomers will use spectrometers to look for 
evidence of chemical changes in JupiterUs atmosphere. Some of the 
species observed might be those only present in the deep 
atmosphere and carried up by the fireball (if the explosion occurs 
deep enough). Others will be the result of changes to the 
chemistry of the upper atmosphere, taking place because of the 
energy deposited there by the impacts or because of the additional 
particulates.
 
 
9. What Do Scientists Expect to Learn from All of This?
 
		To give a simple and succinct answer to the title of 
this section, scientists hope to learn more about comets, more 
about Jupiter, and more about the physics of high velocity impacts 
into a planetary atmosphere. Something has already been learned 
about comets from the behavior of Shoemaker-LevyJ9 during its 
breakup, as discussed in Section 4. Bits and pieces of what 
everyone hopes will be learned have been noted in Sections 5 
through 8. A more complete summary follows.
 
If the fragments explode above the clouds, there should be enough 
light reflected from various Jovian satellites to take spectra of 
the explosions. Since the atmosphere of Jupiter contains very few 
heavier elements to contaminate the spectra, they could give a 
great deal of information about the composition of cometary 
solids. If the fragments explode below the clouds, then 
spectroscopy must wait until the impact sites rotate into view 
from Earth. By that time everything will have cooled a great deal, 
and the cometary component will have been diluted by mixing with 
the Jovian atmosphere, making such study difficult. In that case 
the Jovian material itself may prove of interest, with 
spectroscopic study giving new knowledge of JupiterUs deeper 
atmospheric composition.
 
It seems somewhat more certain that new knowledge of JupiterUs 
atmosphere will be obtained, even if predictions differ as to 
exactly what that new knowledge will be. There is nearly unanimous 
agreement that the impacts will cause observable changes in 
Jupiter, at least locally at the impact sites. These may include 
changes in the visible appearance of the clouds, locally or more 
widely, measurable temperature fluctuations, again locally or more 
widely, composition changes caused by material brought up from 
below the clouds (if the fragments penetrate that deeply), and/or 
chemical reactions brought about by the thermal pulse and the 
introduction of cometary material. Any dynamic processes such as 
these will give a new and better understanding of the structure of 
JupiterUs atmosphere, perhaps of its motion as well as its static 
structure.
 
If sufficient material impacts JupiterUs rings or especially the 
ring satellites, then there should be local brightening caused by 
the increase in reflecting area due to the introduction of new 
material. These new ring particles will each take up their own 
orbits around Jupiter, gradually spreading out and causing local 
brightening followed by slow fading into the general ring 
background. Careful mapping of that brightening and fading will 
reveal a great deal about the structure and dynamics of the rings. 
Many believe that impacts on those small inner satellites are the 
source of the rings, the reason for their existence. Enhancement 
of the rings from Shoemaker-LevyJ9 impacts would be strong 
confirmation of this idea. Similarly, the interaction of cometary 
dust with the magnetosphere and with the Io torus will be quite 
informative, if the dust density proves sufficient to cause 
observable effects. Radio telescopes will be active in the 
magnetospheric studies, along with optical spectroscopy of the 
ions and atoms in the torus.
 
Last, but far from least, the physics of the impact phenomena 
themselves, determined from the reflected light curves and from 
spectra, will be most instructive. Note the inability of 
scientists to agree on the level of JupiterUs atmosphere at which 
the terminal explosion will occur. (A few even believe that there 
will be no terminal explosion or that it will occur so deep in 
that atmosphere as to be completely unobservable.) Entry phenomena 
on this scale cannot be reproduced, even by nuclear fusion 
explosions, and have never before been observed. Better knowledge 
of the phenomena may allow scientists to predict more accurately 
just how serious could be the results of future impacts of 
various-sized bodies on Earth, as well as to determine their 
effects in the past as registered by the fossil record.
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
Appendix A
Comparative Tables
 
Table 1. Energy comparisons.*
 
           Energy, J           Energy, Relative
 
Two 3,500-lb. cars colliding head-on at 55Jmph
           9.6 x 10^5          1
 
Explosion of 1 U.S. ton of TNT
           4.2 x 10^9          4,271
 
Explosion of a 20-megaton fusion bomb
           8.4 x 10^16         87,500,000,000
 
Total U.S. annual electric power production, 1990
           1 x 1019            10,400,000,000,000
 
Energy released in last second of 10^13 kg fragment of Shoemaker-
LevyJ9
         ~ 9 x 10^21           9,375,000,000,000,000
 
Total energy released by 1013-kg fragment of Shoemaker-LevyJ9
           1.8 x 10^22         18,750,000,000,000,000
 
Total sunlight on Jupiter for one day
           6.6 x 10^22         68,750,000,000,000,000
 
 
*1 BTU = 252 (small) calories = 1,055JJ = 2.93 Jx 10-4JkWh.
 
 
 
 
Table 2. Power comparisons.* 
 
Power Producer    Power, MW        Power, Relative
 
Hoover Dam        1,345            1
 
Grand Coulee Dam, final plant
                  9,700            7.2
 
Annual average, sum of all U.S. power plants
                  320,000          238
 
Average, impact of 1013-kg fragment of Shoemaker-Levy 9,
final sec       ~ 9 x 10^15        6,700,000,000,000
 
Sun               3.8 x 1020       280,000,000,000,000,000
 
 
*1 horsepower = 745.7JW = 7.457  x 10-4JMW.
 
 
 
 
Table 3. Size comparisons.*
 
Object                    Radius, km               Volume, km^3 
 
Jupiter                 71,350 (Equatorial)        1.4 x 10^15
                        67,310 (Polar)
 
Earth                   6,378 (Equatorial)         1.1 x 10^12
                        6,357 (Polar)
 
Comet Shoemaker-LevyJ9  4.5 (Equivalent sphere)    382
 
Comet Halley            7.65 x 3.60 x 3.61         365
 
 
*1 mi. = 1.609 km
 
 
 
 
Table 4. Brightness comparisons.
 
Object  Magnitude Vo(V Mag. at Opposition)     Relative Brightness
		
Largest fragment of Shoemaker-Levy 9 during last second
        ~ -10                                  1,000
 
Jupiter   -2.5                                 1
 
Ganymede   4.6                                 1/692
 
Io         5.0                                 1/1,000
 
Largest fragment of Shoemaker-Levy 9 as viewed today
           23.7                                1/30,000,000,000
 
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
Appendix B
The K-T Event
 
		Sixty-five million years ago about 70% of all species 
then living on Earth disappeared within a very short period. The 
disappearances included the last of the great dinosaurs. 
Paleontologists speculated and theorized for many years about what 
could have caused this Rmass extinction,S known as the K-T event 
(Cretaceous-Tertiary Mass Extinction event). Then in 1980 Alvarez, 
Alvarez, Asaro, and Michel reported their discovery that the 
peculiar sedimentary clay layer that was laid down at the time of 
the extinction showed an enormous amount of the rare element 
iridium. First seen in the layer near Gubbio, Italy, the same 
enhancement was soon discovered to be worldwide in that one 
particular 1-cm (0.4-in.) layer, both on land and at sea. The 
Alvarez team suggested that the enhancement was the product of a 
huge asteroid impact. 
 
On Earth most of the iridium and a number of other rare elements 
such as platinum, osmium, ruthenium, rhodium, and palladium are 
believed to have been carried down into EarthUs core, along with 
much of the iron, when Earth was largely molten. Primitive 
RchondriticS meteorites (and presumably their asteroidal parents) 
still have the primordial solar system abundances of these 
elements. A chondritic asteroid 10Jkm (6Jmi.) in diameter would 
contain enough iridium to account for the worldwide clay layer 
enhancement. This enhancement appears to hold for the other 
elements mentioned as well.
 
Since the original discovery many other pieces of evidence have 
come to light that strongly support the impact theory. The high 
temperatures generated by the impact would have caused enormous 
fires, and indeed soot is found in the boundary clays. A 
physically altered form of the mineral quartz that can only be 
formed by the very high pressures associated with impacts has been 
found in the K-T layer.
 
Geologists who preferred other explanations for the K-T event 
said, Rshow us the crater.S In 1990 a cosmochemist named Alan 
Hildebrand became aware of geophysical data taken 10Jyears earlier 
by geophysicists looking for oil in the Yucatn region of Mexico. 
There a 180-km (112-mi.) diameter ring structure called 
RChicxulubS seemed to fit what would be expected from a 65-
million-year-old impact, and further studies have largely served 
to confirm its impact origin. The Chicxulub crater has been age 
dated (by the 40Ar/39Ar method) at 65JmillionJyears! Such an 
impact would cause enormous tidal waves, and evidence of just such 
waves at about that time has been found all around the Gulf of 
Mexico. Similarly, glassy debris of appropriate age called 
tektites (and their decomposition products), which are produced by 
large impacts, have been found all around the Gulf.
 
One can never prove that an asteroid impact Rkilled the 
dinosaurs.S Many species of dinosaurs (and smaller flora and 
fauna) had in fact died out over the millions of years preceding 
the K-T event. The impact of a 10-km asteroid would most certainly 
have been an enormous insult to life on Earth. Locally there would 
have been enormous shock wave heating and fires, a tremendous 
earthquake, hurricane winds, and trillions of tons of debris 
thrown everywhere. It would have created months of darkness and 
cooler temperatures globally. There would have been concentrated 
nitric acid rains worldwide. Sulfuric acid aerosols may have 
cooled Earth for years. Life certainly could not have been easy 
for those species which did survive. Fortunately such impacts 
occur only about once every hundred million years.
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"
 
Appendix C
The Probability of Collisions with Earth
 
		Most bodies in the solar system with a visible solid 
surface exhibit craters. On Earth we see very few because 
geological processes such as weathering and erosion soon destroy 
the obvious evidence. On bodies with no atmosphere, such as 
Mercury or the Moon, craters are everywhere. Without going into 
detail, there is strong evidence of a period of intense cratering 
in the solar system that ended about 3.9JbillionJyears ago. Since 
that time cratering appears to have continued at a much slower and 
fairly uniform rate. The cause of the craters is impacts by comets 
and asteroids. Most asteroids follow sensibly circular orbits 
between the planets Mars and Jupiter, but all of these asteroids 
are perturbed, occasionally by each other and more regularly and 
dramatically by Jupiter. As a result some find themselves in 
orbits that cross that of Mars or even Earth. Comets on the other 
hand, as noted in Section 2, follow highly elongated orbits that 
often come close to Earth or other major bodies to begin with. 
These orbits are greatly affected if they come anywhere near 
Jupiter. Over the eons every moon and planet finds itself in the 
wrong place in its orbit at the wrong time, many times, and 
suffers the insult of a major impact.
 
EarthUs atmosphere protects us from the multitude of small debris, 
the size of grains of sand or pebbles, thousands of which pelt our 
planet every day. The meteors in our night sky are visible 
evidence of bodies of this type burning up high in the atmosphere. 
In fact, up to a diameter of about 10Jm (33Jft.) most stony 
meteoroids are destroyed in the atmosphere in a terminal 
explosion. Obviously some fragments do reach the ground, because 
we have stony meteorites in our museums. Such falls are known to 
cause property damage from time to time. On OctoberJ9, 1992, a 
fireball was seen streaking across the sky all the way from 
Kentucky to New York. A 27-lb. stony meteorite (chondrite) from 
the fireball fell in Peekskill, New York, punching a hole in the 
rear end of an automobile parked in a driveway and coming to rest 
in a shallow depression beneath it. Falls into a Connecticut 
dining room and an Alabama bedroom are other well documented 
incursions in this century. A 10-m body typically has the kinetic 
energy of about five Hiroshima fission bombs, however, and the 
shock wave it creates can do considerable damage even if nothing 
but comparatively small fragments survive to reach the ground. 
 
Many fragments of a 10-m iron meteoroid will reach the ground. The 
only well studied example of such a fall in recent times took 
place in the Sikhote-Alin Mountains of eastern Siberia on 
FebruaryJ12, 1947. About 150JU.S. tons of fragments reached the 
ground, the largest intact fragment weighing 3,839Jlb. The 
fragments covered an area of about 1J4J2Jkm (0.6J4J1.2Jmi.), 
within which there were 102Jcraters greater than 1Jm in diameter, 
the largest of them 26.5Jm (87Jft), and about 100Jmore smaller 
craters. If this small iron meteorite had landed in a city, it 
obviously would have created quite a stir. The effect of the 
larger pieces would be comparable to having a supersonic auto 
suddenly drop in! Such an event occurs about once per decade 
somewhere on Earth, but most of them are never recorded, occurring 
at sea or in some remote region such as Antarctica. It is a fact 
that there is no record in modern times of any person being killed 
by a meteorite.
 
It is the falls larger than 10Jm that start to become really 
worrisome. The 1908 Tunguska event described in SectionJ7 was a 
stony meteorite in the 100-m class. The famous meteor crater in 
northern Arizona, some 4,000Jft. in diameter and 600Jft. deep, was 
created 50,000Jyears ago by a nickel-iron meteorite perhaps 60Jm 
in diameter. It probably survived nearly intact until impact, at 
which time it was pulverized and largely vaporized as its 6-
7J4J1016 joules of kinetic energy were rapidly dissipated. An 
explosion equivalent to some 15Jmillion tons of TNT creates quite 
a bang! Falls of this class occur once or twice every 1,000Jyears.
 
There are now over 100Jring-like structures on Earth recognized as 
definite impact craters. Most of them are not obviously craters, 
their identity masked by heavy erosion over the centuries, but the 
minerals and shocked rocks present make it clear that impact was 
their cause. The Ries Crater in Bavaria is a lush green basin some 
25Jkm (15Jmi.) in diameter with the city of Nrdlingen in the 
middle. FifteenJmillion years ago a 1,500-m (5,000-ft.) asteroid 
or comet hit there, excavating more than a trillion tons of 
material and scattering it all over central Europe. This sort of 
thing happens about once every million years or so. Another step 
upward in size takes us to Chicxulub, described in detail in 
AppendixJB, an event that occurs once in 50-100JmillionJyears. 
Chicxulub is the largest crater known which seems definitely to 
have an impact origin, but there are a few ring-like structures 
that are 2-3Jtimes larger yet about which geologists are 
Rsuspicious.S
 
There are now more than 150Jasteroids known that come nearer to 
the Sun than the outermost point of EarthUs orbit. These range in 
diameter from a few meters to about 8Jkm. A working group chaired 
by D. Morrison estimates that there are some 2,100Jsuch asteroids 
larger than 1Jkm and perhaps 320,000Jlarger than 100Jm, the size 
that caused the Tunguska event and the Arizona meteor crater. An 
impact by one of the latter in the wrong place would be a great 
catastrophe, but it would not threaten civilization. An impact by 
an 8-km object is in the mass extinction category. In addition 
there are many comets in the 1-10-km class, 15Jof them in short-
period orbits that pass inside EarthUs orbit, and an unknown 
number of long-period comets. Virtually any short-period comet 
among the 100Jor so not currently coming near to Earth could 
become dangerous after a close passage by Jupiter.
 
This all sounds pretty scary. However, as noted earlier, no human 
in the past 1,000 years is known to have been killed by a 
meteorite or by the effects of one impacting. (There are ancient 
Chinese records of such deaths.) An individualUs chance of being 
killed by a meteorite is ridiculously small as compared to death 
by lightning, volcanism, earthquake, or hurricane, to say nothing 
of the multitude of human-aided events. That small probability was 
unlikely to have been any consolation to the dinosaurs, however. 
For this reason astronomers today are conducting ever-increasing 
searches for all of the larger asteroids that could become 
dangerous. Once discovered, with a few years of warning, there is 
every reason to believe that a space mission could be mounted Rto 
shove them aside."
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"

 
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *                                                                           *
 *                       Frequently Asked Questions about                    *
 *            the Collision of Comet Shoemaker-Levy 9 with Jupiter           *
 *                                                                           *
 *                         Last Updated 17-Apr-1994                          *
 *                          90 Days until Impact A                           *
 *                                                                           *
 *     The following is a list of answers to frequently asked questions      *
 * concerning the collision of comet Shoemaker-Levy 9 with Jupiter.  Thanks  *
 * to all those who have contributed.  Contact Dan Bruton ([email protected])   *
 * or John Harper ([email protected]) with comments, additions, corrections,  *
 * etc.  A PostScript version and updates of this FAQ list are available via *
 * anonymous ftp to tamsun.tamu.edu (128.194.15.32) in the /pub/comet        *
 * directory.  To subscribe to the "Comet/Jupiter Collision mailing list",   *
 * send mail to [email protected] (no subject) with the message: *
 *                                                                           *
 *     SUBSCRIBE SL9 Firstname Lastname                                      *
 *                                                                           *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 
RECENT CHANGES TO THIS FAQ LIST
 
        Question 1.3 : More GIF's and PostScript Graphics
        Question 2.3 : Location of crater chains on the Moon
        Question 2.9 : JPL's SL9 Educator's Book
                           and Modified FTP and WWW Sites  
 
GENERAL QUESTIONS
 
 Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 Q1.2: Who are Shoemaker and Levy?
 Q1.3: Where can I find a GIF image of this comet?
 Q1.4: What will be the effect of the collision?
 
SPECIFICS
 
 Q2.1: What are the impact times and impact locations of the comet fragments?
 Q2.2: What are the orbital parameters of the comet?
 Q2.3: Why did the comet break apart?
 Q2.4: What are the sizes of the fragments?
 Q2.5: How long is the fragment train?
 Q2.6: Will Hubble or Galileo be able to observe the collisions?
 Q2.7: How can I observe the effects of the collisions?
 Q2.8: To whom do I report my observations?
 Q2.9: Where can I find more information?
 
GENERAL QUESTIONS
 
Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 
     Yes, The shattered comet Shoemaker-Levy 9 (1993e) is expected to 
collide with Jupiter over a 5.6 day period in July 1994.  The first of 21 
comet fragments is expected to hit Jupiter on July 16, 1994 and the last on 
July 22, 1994.  All components of the comet will hit on the dark farside of 
Jupiter, out of sight from Earth.  The impact of the center of the comet 
train is predicted to occur at about -44 degrees Jupiter latitude at a point 
about 67 degrees east (toward the sunrise terminator) from the midnight 
meridian.  The angle of incidence of the impacts is between 41 and 42 degrees
for all the fragments.
     These new impact point estimates from Sekanina, Chodas, and Yeomans
are much closer to the morning terminator of Jupiter than the old estimates.
Although they are still all on the far side as viewed from the Earth, they are
now only 5-9 degrees behind the limb.  About 20 - 40 minutes after each hit,
the impact points will rotate past the limb of Jupiter as seen from Earth.
After these points cross the limb it will take another 17 minutes before
they cross the morning terminator into sunlight.
 
Q1.2: Who are Shoemaker and Levy?
 
     Eugene and Carolyn Shoemaker and David H. Levy found the 13.8 magnitude
comet on March 25, 1993 on photographic plates taken on March 22, 1993.  The
photographs were taken at Palomar Mountain in Southern California with a
0.46 meter Schmidt camera and were examined using a stereomicroscope to
reveal the comet [2,14].  James V. Scotti confirmed their discovery with the
Spacewatch Telescope at Kitt Peak in Arizona.  See [11] for more information
about the discovery.
 
Q1.3: Where can I find a GIF image of this comet?
 
     GIF images can be obtained via anonymous ftp or to SEDS.LPL.Arizona.edu
(128.196.64.66) in the /pub/astro/SL9 directory.  This site also supports
gopher.  Below is a list of the images at this site.  The files are listed 
here in reverse chronological order.  Most of the images are accompanied by 
a text file giving a description of the image.
 
sl90216.gif      February 16, 1994 Image from Kitt Peak (J. Scotti)
sl90216s.gif     Gray-stretched inverse version of sl90216.gif
sl90216x.gif     Enlarged inverse version of sl90216.gif
wfpclevy.gif     Photo Montage of January 24-27 Imaging of SL9 from HST
sl9hst.gif       Post-fix HST Mosaic of SL9 (Jan. 24-27)
sl90121.gif      January 21, 1994 Image from Kitt Peak (R. Jedicke)
sl90121x.gif     Enlarged view of sl90121.gif
sl9compl.gif     Six month comparison image of SL9 (Labeled)
sl9comp.gif      Six month comparison image of SL9 (Not Labeled)
1993eha.gif      View of the comet from HST
1993ehb.gif      From HST, focused on the center of the train of fragments
1993esw.gif      Ground-based view of the comet
sl03302b.gif     March 30, 1993 Image from Kitt Peak (J. Scotti)
sl03302c.gif     Pseudo-color version of sl03302b.gif
sl9_930330.gif   March 30, 1993 image of SL9, Spacewatch Telescope-J. Scotti
sl9w_930328.gif  March 28, 1993 image of SL9
shoelevy.gif     An early GIF image of SL9
 
   The following is a list of other collision related GIF graphics and MPEG 
animations that are also available at this site:
 
approach.gif       View of last 18 hours of trajectory, from Earth
earthview.gif      Full-disk view from Earth
earthviewzoom.gif  Close-up view from Earth 
vgr2view.gif       Full-disk view from Voyager 2 
vgr2viewzoom.gif   Close-up view of impact sites from direction of Voyager 2
galview.gif        View from Galileo
ulysview.gif       View from Ulysses 
poleview.gif       View from beneath Jupiter 
orbjupplane.gif    SL9's orbit projected into Jupiter's orbit plane 
orbsun.gif         SL9's orbit as seen from the Sun 
earthjup.gif       Jupiter-Facing Hemispheres of Earth at Impact Times of SL9
impact.gif         Graph of impact times with moon eclipses
index.gif          Mosaic of all images in this directory
mitwave1.gif       Frame from MIT Flow Visualization Lab. Simulation
mitwave2.gif       Frame from MIT Flow Visualization Lab. Simulation
mitwave.mpg        MIT Flow Visualization Lab. Simulation Animation
vidjv.mpg          Animation of SL9 entering Jupiter's Atmosphere
visejz.mpg         Animation of explosion produced by SL9 entering Jupiter
sl9rend.gif        Rendering 3 views of comet-Jupiter collision
sl9rend1.gif       Larger rendering comet-Jupiter from Earth
sl9rend2.gif       Larger rendering comet-Jupiter from Voyager 2
sl9rend3.gif       Larger rendering comet-Jupiter from south pole
 
Q1.4: What will be the effect of the collision?
 
     Each comet fragment will enter the atmosphere at a speed of 130,000 mph
(60 km/s).  At an altitude of 100 km above the visible cloud decks,
aerodynamic forces will overwhelm the material strength of the comet,
beginning to squeeze it and tear it apart.  Five seconds after entry, the
comet fragment will deposit its kinetic energy of around 10^28 ergs
(equivalent to around 200,000 megatons of TNT) at 100-150 km below the
cloud layer [19].  Bigger fragments will have more energy and go deeper.
     The hot (30,000 K) gas resulting from the stopped comet will explode,
forming a fireball similar to a nuclear explosion, but much larger.
The visible fireball will only rise 100 km or so above the cloudtops.
Above that height the density will drop so that it will become transparent.
The fireball material will continue to rise, reaching a height of perhaps
1000 km before falling back down to 300 km.  The fireball will spread out
over the top of the stratosphere to a radius of 2000-3000 km from the point
of impact (or so the preliminary calculations say).  The top of the resulting
shock wave will accelerate up out of the Jovian atmosphere in less than two
minutes, while the fireball will be as bright as the entire sunlit surface of
Jupiter for around 45 sec [18].  The fireball will be somewhat red, with a
characteristic temperature of 2000 K - 4000 K (slightly redder than the sun,
which is 5000 K).  Virtually all of the shocked cometary material will rise
behind the shock wave, leaving the Jovian atmosphere and then splashing back
down on top of the stratosphere at an altitude of 300 km above the clouds
[unpublished simulations by Mac Low & Zahnle].  Not much mass is involved in
this splash, so it will not be directly observable.  The splash will be
heavily enriched with cometary volatiles such as water or ammonia, and so may
contribute to significant high hazes.
        Meanwhile, the downward moving shock wave will heat the local clouds,
causing them to buoyantly rise up into the stratosphere.  This will allow
spectroscopists to attempt to directly study cloud material, a unique
opportunity to confirm theories of the composition of the Jovian clouds.
Furthermore, the downward moving shock may drive seismic waves (similar to
those from terrestrial earthquakes) that might be detected over much of the
planet by infrared telescopes in the first hour or two after each impact.
The strength of these two effects remains a topic of research.
        Finally, the disturbance of the atmosphere will drive internal
gravity waves ("ripples in a pond") outwards.  Over the days following the
impact, these waves will travel over much of the planet, yielding information
on the structure of the atmosphere if they can be observed (as yet an
open question).
     The "wings" of the comet will interact with the planet before and
after the collision of the major fragments.  The so-called "wings" are
defined to be the distinct boundary along the lines extending in both
directions from the line of the major fragments; some call these 'trails'.
Sekanina, Chodas and Yeomans have shown that the trails consist of larger
debris, not dust: 5-cm rock-sized material and bigger (boulder-sized and
building-sized).  Dust gets swept back above (north) of the trail-fragment
line due to solar radiation pressure.  The tails emanating from the major
fragments consist of dust being swept in this manner.  Only the small portion
of the eastern debris trail nearest the main fragments will actually impact
Jupiter, according to the model, with impacts starting only a week before
the major impacts.  The western debris trail, on the other hand, will impact
Jupiter over a period of months following the main impacts, with the latter
portion of the trail actually impacting on the front side of Jupiter as viewed
from Earth.
        The injection of dust from the wings and tail into the Jovian system
may have several consequences.  First, the dust will absorb many of the
energetic particles that currently produce radio emissions in the Jovian
magnetosphere.  The expected decline and recovery of the radio emission may
occur over as long as several years, and yield information on the nature and
origin of the energetic particles.  Second, the dust may actually form a
second faint ring around the planet.
     There are now two technical papers [18,19] on the atmospheric consequences
of the explosions available via anonymous ftp from oddjob.uchicago.edu in the
pub/jupiter directory.  The paper and figures are available in UNIX compressed
PostScript format; a couple of the computational figures are also available
in TIFF format.
 
SPECIFICS
 
Q2.1: What are the impact times and impact locations of the comet fragments?
 
     The following table gives the latest impact predictions.  The 21 major
fragments are denoted A through W in order of impact, with letters I and O
not used.  The predicted impact times for F, G, K, Q, R, and W have moved
slightly later (by up to 0.02 days), while those for H, L, and P are now
slightly earlier.  The impact points have generally moved a few tenths of a
degree closer to the limb as seen from the Earth.  Fragments J and M have
been deleted from the table because they have disappeared: they are not
visible in the HST image taken in late January.
 
Predictions as of 1994 February 23 by
P.W. Chodas, D.K. Yeomans and Z. Sekanina
JPL/Caltech
 
+=============================================================================+
| Fragment  UT Date/Hour  Jovicentric  Meridian Angle   Angle  Probability of |
|            of Impact     Latitude     Angle   S-F-J   E-J-F  viewing impact |
|          month dy hr mn    (deg)      (deg)   (deg)   (deg)  Io  Eu  Ga  Ca |
+=============================================================================+
|  A = 21   July 16 19      -43.26      64.43   73.95   98.73   0   3   3   3 |
|  B = 20   July 17 03      -43.34      64.73   74.18   98.49   3   3   3   3 |
|  C = 19   July 17 06      -43.37      64.90   74.30   98.36   3   2   3   3 |
|  D = 18   July 17 12      -43.42      65.11   74.46   98.20   3   0   3   3 |
|  E = 17   July 17 15      -43.80      64.98   74.50   98.21   1   0   3   3 |
|  F = 16   July 18 00      -44.24      63.09   73.40   99.42   0   0   3   3 |
|  G = 15   July 18 07      -44.19      65.00   74.66   98.09   0   0   3   3 |
|  H = 14   July 18 19      -44.04      64.99   74.60   98.13   3   0   0   3 |
|  J = 13   Disappeared                                                       |
|  K = 12   July 19 10      -44.43      66.16   75.51   97.22   0   3   0   3 |
|  L = 11   July 19 21      -44.52      65.60   75.17   97.58   0   3   0   3 |
|  M = 10   Disappeared                                                       |
|  N = 9    July 20 10      -44.78      66.40   75.79   96.97   0   3   0   3 |
|  P = 8    July 20 15      -45.00      65.61   75.34   97.47   3   3   0   3 |
|  Q = 7    July 20 19      -44.54      67.56   76.50   96.19   3   3   0   3 |
|  R = 6    July 21 07      -44.78      70.07   78.27   94.39   1   0   0   3 |
|  S = 5    July 21 15      -44.69      68.07   76.89   95.80   0   0   0   3 |
|  T = 4    July 21 18      -44.10      69.63   77.77   94.80   0   0   0   3 |
|  U = 3    July 21 21      -44.11      69.77   77.88   94.69   0   0   0   3 |
|  V = 2    July 22 04      -44.14      70.09   78.11   94.46   0   0   0   3 |
|  W = 1    July 22 08      -44.24      70.69   78.55   94.02   2   0   0   3 |
+=============================================================================+
| Approximate                                                                 |
| Uncertainty   43 min        0.6        2.5     1.6     1.7                  |
|  (1-sigma)                                                                  |
+=============================================================================+
 
Table Notes:
 
*  Two fragment designations are given: the letter designation is that used
   in a preprint (Sekanina, Chodas, and Yeomans); the numerical designation
   is that used by Jewitt.  Q=7 is the brightest.  Fragments J=13 and M=10
   have been deleted from the table because they are absent from the Hubble
   Space Telescope image taken in late January.  It is also now apparent from
   the HST image that P and Q each consist of two components.  In the above
   table, P refers to component P2=8b, the brighter and more easterly of the
   two P fragments, and Q refers to Q1=7a, the brighter and more southerly of
   the two Q fragments.
 
*  The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.
 
*  Angle S-F-J is the Sun-Fragment-Jupiter angle at impact; values less than
   90 deg indicate a nightside impact: all impacts are on the nightside.
 
*  Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact: all impacts are on the farside as
   viewed from Earth, with the later impacts being closer to the limb.
 
*  The predictions for fragments E and R are more uncertain than those for
   G, H, K, L, Q, S, and W, because the orbits are less well-determined.
 
*  The impact times above include the light time to the Earth (~ 43 minutes).
 
*  The probability that a given Galilean satellite will be in view of an
   impact is given in terms of sigmas: 0 indicates a probability of less than
   68%, 1 indicates 69-95%, 2 indicates 96-99%, and 3 indicates a probability
   greater than 99%.  For example, the probabilities that Io, Europa, and
   Callisto will be in view of the fragment Q impact are all greater than 99%.
 
*  The one-sigma uncertainties specified on the bottom line are average values
   obtained from Monte Carlo analyses for the eight fragments having the best
   orbit solutions.  The same analyses computed the probability that the
   fragments will in fact impact Jupiter is > 99.99%, and the probability that
   any will impact on the near side as viewed from the Earth is < 0.2%.
 
     The following are the 3-sigma (uncertainty) predictions for the
fragment impact times:
 
          on March 1         -  90 min
          on May 1           -  71 min
          on June 1          -  49 min
          on July 1          -  30 min
          on July 15         -  19 min
          at impact - 18 hr  -  10 min
 
The time between impacts is thought to be known with more certainty than the
actual impact times.  This means that if somehow the impact time of the first
fragment can be measured experimentally, then impact times of the fragments
that follow can be predicted with more accuracy.

Q2.2: What are the orbital parameters of the comet?
 
   Comet Shoemaker-Levy 9 is actually orbiting Jupiter, which is most
unusual: comets usually just orbit the Sun.  Only two comets have ever
been known to orbit a planet (Jupiter in both cases), and this was inferred
in both cases by extrapolating their motion backwards to a time before they
were discovered.  S-L 9 is the first comet observed while orbiting a planet.
Shoemaker-Levy 9's previous closest approach to Jupiter (when it broke up)
was on July 7, 1992 according to the new solution; the distance from the
center of Jupiter was about 96,000 km, or about 1.3 Jupiter radii.  The comet
is thought to have reached apojove (farthest from Jupiter) on July 14, 1993
at a distance of about 0.33 Astronomical Units from Jupiter's center.  The
orbit is very elliptical, with an eccentricity of over 0.995.  Computations
by Paul Chodas, Zdenek Sekanina, and Don Yeomans, suggest that the comet has
been orbiting Jupiter for 20 years or more, but these backward extrapolations
of motion are highly uncertain.
     See the PostScript plots called "fig*.ps" at SEDS.LPL.Arizona.EDU or [14]
for a visual representation of the orbit.  The right ascension and declination
of the comet along with some orbital elements can also be obtained via FTP at 
SEDS.LPL.Arizona.EDU in the /pub/astro/SL9 directory in the file called 
"elements.nuc".  This file is updated periodically.
 
Q2.3: Why did the comet break apart?
 
     The comet is thought to have broken apart due to tidal forces on its
closest approach to Jupiter (perijove) on July 7, 1992.  Shoemaker-Levy 9 is
not the first comet observed to break apart.  Comet West shattered in 1976
near the Sun [3].  Astronomers believe that in 1886 Comet Brooks 2 was ripped
apart by tidal forces near Jupiter [2].
     Furthermore, images of Callisto and Ganymede show crater chains which may
have resulted from the impact of a comet similar to Shoemaker-Levy 9 [3,17].
The satellite with the best example of aligned craters is Callisto with 13
crater chains.  There are three crater chains on Ganymede.  These were first
thought to be from basin ejecta; in other words secondary craters.  
     There are also a few examples on our Moon.  Jay Melosh and Ewen Whitaker 
have identified 2 possible crater chains on the moon which would be generated 
by near-Earth tidal breakup.  One is called the "Davy chain" and it is very
tiny but shows up as a small chain of craters aligned back toward Ptolemaeus. 
In near opposition images, it appears as a high albedo line; in high phase 
angle images, you can see the craters themselves.  The second is between 
Almanon and Tacitus and is larger (comparable to the Ganymede and Callisto 
chains in size and length).               
 
Q2.4: What are the sizes of the fragments?
 
     Using measurements of the length of the train of fragments and a model
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the
parent nucleus of the comet (before breakup) was only about 2 km across [13].
This would imply that the individual fragments are no larger than about 500
meters across.  However, images of the comet taken with the Hubble Space
Telescope in July 1993 indicate that the fragments are 3-4 km in diameter
(3-4 km is an upper limit based on their brightness).  A more elaborate tidal
disruption model by Sekanina, Chodas and Yeomans [20] predicts that the
original comet nucleus was at least 10 km in diameter.  This means the largest
fragments could be 3-4 km across, a size consistent with estimates derived
from the Hubble Space Telescope's July 1993 observations.
     The new images, taken with the Hubble telescope's new Wide Field and
Planetary Camera-II instrument on January 24-27, 1994, have given us an even 
clearer view of this fascinating object, which should allow a refinement of  
the size estimates.  In addition, the new images show strong evidence for 
continuing fragmentation of some of the remaining nuclei, which will be 
monitored by the Hubble telescope over the next several months.
 
Q2.5: How long is the fragment train?
 
     The angular length of the train was about 51 arcseconds in March 1993 [2].
The length of the train then was about one half the Earth-Moon distance.
In the day just prior to impact, the fragment train will stretch across 20
arcminutes of the sky, more that half the Moon's angular diameter.  This
translates to a physical length of about 5 million kilometers.  The train
expands in length due to differential orbital motion between the first and
last fragments.  Below is a table with data on train length based on Sekanina,
Chodas, and Yeomans's tidal disruption model:
 
           +=============================================+
           |    Date    Angular Length  Physical Length  |
           |               (arcsec)          (km)        |
           +=============================================+
           |  93 Mar 25       49            158,000      |
           |     Jul  1       67            265,000      |
           |  94 Jan  1      131            584,000      |
           |     Feb  1      161            669,000      |
           |     Mar  1      200            762,000      |
           |     Apr  1      255            893,000      |
           |     May  1      319          1,070,000      |
           |     Jun  1      400          1,366,000      |
           |     Jul  1      563          2,059,000      |
           |     Jul 15      944          3,593,000      |
           |    Impact A    1286          4,907,000      |
           +=============================================+
 
Q2.6: Will Hubble or Galileo be able to observe the collisions?
 
     The Hubble Space Telescope, like earthlings, will not be able to see the
collisions but will be able to monitor atmospheric changes on Jupiter. The new
impact points are more favorable for viewing from spacecraft: it can now be
stated with certainty that the impacts will all be visible to Galileo, and now
at least some impacts will be visible to Ulysses.  Although Ulysses does not
have a camera, it will monitor the impacts at radio wavelengths.  The impact
points are also viewable by both Voyager spacecraft, especially Voyager 2.
However, it is doubtful that the Voyagers will image the impacts because the
onboard software that controls the cameras has been deleted, and there is
insufficient time to restore and test the camera software.  The only Voyager
instruments likely to observe the impacts are the ultraviolet spectrometer
and planetary radio astronomy instrument.  Voyager 1 will be 52 AU from
Jupiter and will have a near-limb observation viewpoint.  Voyager 2 will be in
a better position to view the collision from a perspective of looking directly
down on the impacts, and it is also closer at 41 AU.
        Galileo will get a direct view of the impacts rather than the grazing
limb view previously expected.  The Ida image data playback is scheduled to
end at the end of June, so there should be no tape recorder conflicts with
observing the comet fragments colliding with Jupiter.  The problem is how to
get the most data played back when Galileo will only be transmitting at 10 bps.
One solution is to have both Ulysses and Galileo record the event and and store
the data on their respective tape recorders.  Ulysses observations of radio
emissions data will be played back first and will at least give the time of
each comet fragment impact.  Using this information, data can be selectively
played back from Galileo's tape recorder.  From Galileo's perspective, Jupiter
will be 60 pixels wide and the impacts will only show up at about 1 pixel,
but valuable science data can still collected in the visible and IR spectrum
along with radio wave emissions from the impacts.
 
Q2.7: How can I observe the effects of the collisions?
 
     One might be able to detect atmospheric changes on Jupiter using
photography, or CCD imaging.  It is important, however, to observe Jupiter
for several months in advance in order to know which features are due to 
impacts and which are naturally occurring.  It appears more and more likely
that most effects will be quite subtle.  Without a large ( > 15" ?) telescope
and good detector, little is likely to be seen.  There is a MSDOS program
written by Lenny Abbey that displays information about Jupiter's major
features and predicts the locations of Jupiter's moons, the Great Red Spot,
and the central meridian System I and System II longitudes.  See the file
called "jupe.description" in tamsun.tamu.edu in the /pub/comet directory
for more information about this program.
     One may be able to witness the collisions indirectly by monitoring the
brightness of the Galilean moons that may be behind Jupiter as seen from
Earth.  However, current calculations suggest that the brightenings may
be as little as 0.05% of the sunlit brightness of the moon [18].  If Io can
be caught in eclipse but visible from the earth during an impact, prospects
will improve significantly.  The MSDOS program "galsat51.zip" will calculate 
and display the locations of the Galilean satellites for the predicted impact 
times and can be obtained via ftp from tamsun.tamu.edu in the /pub/comet 
directory.  One could monitor the moons using a photometer, a CCD camera, or 
a video camera pointed directly into the eyepiece of a telescope.  If you do 
video you can get photometric information by frame grabbing and treating these
like CCD frames (applying darks, biases, and flats) [23].  
     The cutoff of radio emissions due to the entry of cometary dust into the
Jovian magnetosphere during the weeks around impact may be clear enough to be
detected by small radio telescopes.  Furthermore, impacts may be directly
detectable in radio frequencies.  Some suggest to listen in on 15-30 MHz during
the comet impact.  So it appears that one could use the same antenna for both 
the Jupiter/Io phenomenon and the Jupiter/comet impact.  There is an article 
in Sky & Telescope magazine which explains how to build a simple antenna for 
observing the Jupiter/Io interaction [4,24,25].  This simple antenna is less 
directional that a dipole or long-wire antenna.  See the file called 
"io_jup.radio" on tamsun.tamu.edu in the /pub/comet directory for more 
information. 
 
Q2.8: To whom do I report my observations?
 
   The Association of Lunar and Planetary Observers (ALPO) will distribute a 
handbook to interested observers.  Also, observation forms by Steve Lucas are 
available via ftp at tamsun.tamu.edu in the /pub/comet directory.  These 
forms also contain addresses of "Jupiter Watch Program" section leaders.  
"jupcom.zip" contains Microsoft Write files.  For addresses of ALPO, Steve
Lucas and other Jupiter recorders see the January 1994 issue of Sky & 
Telescope magazine [14].
 
Q2.9: Where can I find more information?
 
     The SL9 educator book put out by JPL is in the /pub/astro/SL9/EDUCATOR 
directory of SEDS.LPL.Arizona.edu.
 
===============================================================================
   FTP SITE NAME       IP ADDRESS       DIRECTORY              CONTENTS
===============================================================================
SEDS.LPL.Arizona.EDU (128.196.64.66)  /pub/astro/SL9         Images & Info
tamsun.tamu.edu      (128.194.15.32)  /pub/comet             Images & Info
oddjob.uchicago.edu                   /pub/jupiter           Article & figures
jplinfo.jpl.nasa.gov (137.78.104.2)   /news and /images      Images
ftp.cicb.fr          (129.20.128.34)  /pub/Images/ASTRO/hst  Images
 
===============================================================================
     WORLD WIDE WEB SITES                                         CONTENTS
===============================================================================
http://seds.lpl.arizona.edu/sl9/sl9.html                       Images and Info
http://pscinfo.psc.edu/general/research/mac_low/mac_low.html   Animations
http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html   Info and Images
 
REFERENCES
 
 [1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
 [2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
       page 38-39.
 [3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
       chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
 [4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
 [5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
 [6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
 [7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
 [8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
       September 1993, page 18.
 [9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
 [10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
 [11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
 [12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
       of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
 [13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
       Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
 [14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
       January 1994, page 40-44.
 [15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
 [16] "AstroNews", Astronomy, January 1994, page 19.
 [17] "AstroNews", Astronomy, February 1994, page 16.
 [18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
       Comet Shoemaker Levy 9", submitted to Icarus October 29, 1993.
 [19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
       Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
       submitted to Science on 10 February 1994.
 [20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the
       Appearance of Periodic Comet Shoemaker-Levy 9", submitted to Astronomical
       Journal, November 1993.
 [21] "On a collision Course with Jupiter", Mercury, Nov-Dec 1993, page 15-16.
 [22] "Timing the Crash", Sky & Telescope, February 1994, page 11.
 [23] "Capturing Jupiter on Video" Sky & Telescope, September 1993, page 102.
 [24] "Advanced Amateur Astronomy", Gerald North, (1991), page 296-298.
 [25] "Backyard Radio Astronomy", Astronomy, March 1983, page 75-77.
 
ACKNOWLEDGMENTS
 
     Thanks to Ross Smith for starting a FAQ and to all those who have
contributed :  Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke, Rik Hill,
Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke, David H. Levy,
Eugene and Carolyn Shoemaker, Jim Scotti, Richard A. Schumacher,
Louis A. D'Amario, John McDonald, Michael Moroney, Byron Han, Wayne Hayes,
David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki, Jeffrey A Foust,
Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina, Don Yeomans,
Richard Schmude, Lenny Abbey, Chris Lewicki, the Students for the Exploration 
and Development of Space (SEDS), and David A. Seal.
 
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

From: [email protected] (David M. Seidel)
Newsgroups: sci.space.news
Subject: SL-9  Ch. 8a  How Can These Impacts & Their Consequences Be Studied? - Space-Based
Date: 15 Apr 1994 08:39:07 -0700
Organization: Jet Propulsion Laboratory
Sender: [email protected]
 
8a. How Can These Impacts and Their Consequences be Studied?
 
Space-Based	
		There are at least four spacecraft -- Galileo, Ulysses, 
VoyagerJ2, and Clementine -- with some potential to observe the 
Jovian impacts from different vantage points than that of Earth. 
There is also the Hubble Space Telescope (HST), in orbit around 
Earth, which will view the event with essentially the same 
geometry as any Earth-based telescope. HST, however, has the 
advantages of perfect RseeingS (no atmospheric turbulence), very 
low scattered light, ultraviolet sensitivity, and the ability to 
observe much more than twoJhours each day. HST is scheduled to 
devote considerable time to the observation of Shoemaker-LevyJ9 
before as well as during the impacts.
 
The Galileo spacecraft has the best vantage point from which to 
observe the impacts. It is on its way to Jupiter and will be only 
246JmillionJkm away from the planet, less than a third the 
distance of Earth from Jupiter at that time. All of the impacts 
will occur directly in the field of view of its high resolution 
camera and 20!-25! of Jovian longitude from the limb. Images of 
Jupiter will be 60Jpicture elements (pixels) across, although the 
impact site will still be smaller than the resolution of the 
camera. Several instruments besides the camera have potential use, 
including an ultraviolet spectrometer, a near infrared mapping 
spectrometer, and a photopolarimeter radiometer. This last suite 
of instruments could acquire light curves (plots of intensity 
versus time) of the entry and fireball at many wavelengths from 
ultraviolet to thermal infrared (from wavelengths much shorter 
than visible light to much longer).
 
Using Galileo to make these observations will be challenging. The 
amount of data the spacecraft can transmit back to Earth is 
limited by the capability of its low-gain antenna and the time 
available on the receiving antennas of the National Aeronautics 
and Space AdministrationUs (NASAUs) Deep Space Network here on 
Earth. The RcommandsS that tell the spacecraft what to do must be 
sent up several weeks before the fact and before the impact times 
are known to better than about 20Jminutes with 95% certainty. A 
later command that simply triggers the entire command sequence may 
be possible. A lot of data frames can be stored in the Galileo 
tape recorder, but only about 5% of them can be transmitted back 
to Earth, so the trick will be to decide which 5% of the data are 
likely to include the impacts and to have the greatest scientific 
value, without being able to look at any of them first! After the 
fact, the impact times should be known quite accurately. This 
knowledge can help to make the decisions about which data to 
return to Earth.
 
The Ulysses spacecraft was designed for solar study and used a 
gravity assist from flying close to Jupiter to change its 
inclination (the tilt of its path relative to the plane of the 
planets) so it can fly over the poles of the Sun. In July 1994 it 
will be about 378JmillionJkm south of the plane of the planets 
(the ecliptic) and able to RlookS over the south pole of Jupiter 
directly at the impact sites. Unfortunately, Ulysses has no camera 
as a part of its instrument complement. It does have an extremely 
sensitive receiver of radio frequency signals from 1Jto 1000JkHz 
(kilohertz, or kilocycles in older terminology) called URAP 
(Unified Radio and Plasma wave experiment). URAP may be able to 
detect thermal radiation from the impact fireballs once they rise 
sufficiently high above interference from the Jovian ionosphere 
(upper atmosphere) and to measure a precise time history of their 
rapid cooling.
 
The Voyager 2 spacecraft is now far beyond Neptune (its last 
object of study back in 1989 after visiting Jupiter in 1979, 
Saturn in 1981, and Uranus in 1986) and is about 6.4JbillionJkm 
from the Sun. It can look directly back at the dark side of 
Jupiter, but the whole of Jupiter is now only two picture elements 
in diameter as seen by its high-resolution camera, if that 
instrument were to be used. In fact the camera has been shut down 
for several years, and the engineers who knew how to control it 
have new jobs or are retired. It would be very expensive to take 
the camera Rout of mothballsS and probably of limited scientific 
value. Voyager does have an ultraviolet spectrometer which is 
still taking data, and it will probably be used to acquire 
ultraviolet light curves (brightness versus time) of the impact 
phenomena. The possibility of using one or two other instruments 
is being considered, though useful results from them seem less 
likely.
 
A new small spacecraft called Clementine was launched on 
JanuaryJ25 of this year, intended to orbit the Moon and then 
proceed on to study the asteroid Geographos. Clementine has good 
imaging capabilities, but its viewpoint will not be much different 
from EarthUs. The impact sites will still be just over the limb, 
and ClementineUs resolution will be only a few picture elements on 
Jupiter. Since the spacecraft will be in cruise mode at the time, 
on its way to Geographos and not terribly busy, it seems probable 
that attempts will be made to observe RblipsS of light on the limb 
of Jupiter, from the entering fragments or the fireballs or 
perhaps light scattered from cometary material (coma) that has not 
yet entered the atmosphere. Useful light curves could result.
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"

Article: 5587
From: [email protected] (David M. Seidel)
Newsgroups: sci.space.news
Subject: SL-9  Ch. 8b How Can These Impacts and Their Consequences Be Studied? - Ground-Based
Date: 15 Apr 1994 08:40:34 -0700
Organization: Jet Propulsion Laboratory
Sender: [email protected]
 
8b. How Can These Impacts and Their Consequences be Studied?
 
Ground-Based
		Many large telescopes will be available on Earth with 
which to observe the phenomena associated with the Shoemaker-
LevyJ9 impacts on Jupiter in visible, infrared, and radio 
wavelengths. Small portable telescopes can fill in gaps in 
existing observatory locations for some purposes. Imaging, 
photometry, spectroscopy, and radiometry will certainly be carried 
out using a multitude of detectors. Many of these attempts will 
fail, but some should succeed.
 
Apart from the obvious difficulty that the impacts will occur on 
the back side of Jupiter as seen from Earth, the biggest problem 
is that Jupiter in July can only be observed usefully for about 
twoJhours per night from any given site. Earlier the sky is still 
too bright and later the planet is too close to the horizon. 
Therefore, to keep Jupiter under continuous surveillance would 
require a dozen observatories equally spaced in longitude clear 
around the globe. A dozen observatories is feasible, but equal 
spacing is not. There will be gaps in the coverage, notably in the 
Pacific Ocean, where Mauna Kea, Hawaii, is the only astronomical 
bastion.
 
Measuring the light curve of the entering fragments and the post-
explosion fireball can be done only by measuring the light 
reflected from something else, one of JupiterUs satellites or 
perhaps the dust coma accompanying the fragment. That dust coma 
could still be fairly dense out to distances of 10,000Jkm or more 
around each fragment. Moving at 60Jkm/s, it will be almost 
threeJminutes before all of the dust also impacts Jupiter. Proper 
interpretation of such observations will be difficult, however, 
because the area of the Rreflector,S the coma dust particles, will 
be changing as the observations are made. Another complication is 
the brightness of Jupiter itself, which will have to be masked to 
the greatest extent possible. Observations in visible light 
reflected from the satellites will be relatively straightforward 
and can be done with small telescopes and simple photometers or 
imaging devices. This equipment is small enough that it can be 
transported to appropriate sites.
 
Spectroscopy of the entry phenomena via reflected light from one 
of the Galilean satellites could be used to determine the 
composition of the comet and the physical conditions in the 
fireball, if the terminal explosions occur above JupiterUs clouds. 
If the explosion occurs below the clouds, there will be too little 
light to do useful spectroscopy with even the largest telescopes.
 
The impact zone on Jupiter will rotate into sight from Earth about 
20Jminutes after each impact, though quite foreshortened as 
initially viewed. Extensive studies of the zone and the area 
around it can be made at that time. Such studies surely will 
include imaging, infrared temperature measurements, and 
spectroscopy using many of the largest telescopes on Earth. These 
studies will continue for some weeks, if there is any evidence of 
changes in JupiterUs atmosphere and cloud structure as a result of 
the impacts.
 
For example, astronomers will use spectrometers to look for 
evidence of chemical changes in JupiterUs atmosphere. Some of the 
species observed might be those only present in the deep 
atmosphere and carried up by the fireball (if the explosion occurs 
deep enough). Others will be the result of changes to the 
chemistry of the upper atmosphere, taking place because of the 
energy deposited there by the impacts or because of the additional 
particulates.
 
The faint rings of Jupiter, mentioned in Section 5, can be 
usefully observed from the ground at infrared wavelengths. 
Shoemaker-LevyJ9 debris might bring in new ring material by 
hitting the two small satellites embedded in the rings (Metis and 
Adrastea). The rings surely will be monitored for some time using 
infrared imaging array detectors, which are sensitive to 
wavelengths more than eight times as long as red visible light. 
 
In Section 5, note was made of the Jovian magnetosphere, which 
makes its presence known at radio wavelengths, and the Io torus of 
various ions and atoms, which can be mapped spectroscopically. 
Either or both of these could be affected sufficiently by the 
intruding dust from Shoemaker-LevyJ9 to be detectably changed. 
Radio telescopes will surely monitor the former and optical 
telescopes the latter for weeks or months looking for changes. 
JupiterUs intense electromagnetic environment is responsible for 
massive auroral emission near the planetUs poles and less intense 
phenomena across the face of the planet. These may also be 
disrupted by the collisions and/or the dust Rinvasion,S making 
auroral monitoring a useful observing technique.
 
In summary, the phenomena directly associated with each impact 
from entry trail to rising fireball will last perhaps 
threeJminutes. The fallback of ejecta over a radius of a few 
thousand kilometers will last for about threeJhours. Seismic waves 
from each impact might be detectable for a day, and atmospheric 
waves for several days. Vortices and atmospheric hazes could 
conceivably persist for weeks. New material injected into the 
Jovian ring system might be detectable for years. Changes in the 
magnetosphere and/or the Io torus might also persist for some 
weeks or months. There is the potential to keep planetary 
observers busy for a long time!
 
 
 
 
Acknowledgments:
		This booklet is the product of many scientists, all of 
whom have cooperated enthusiastically to bring their best 
information about this exciting event to a wider audience. They 
have contributed paragraphs, words, diagrams, slides, and 
preprints as well as their critiques to this document, which 
attempts to present an event that no one is quite sure how to 
describe. Sincere thanks go to Mike AUHearn, Paul Chodas, Gil 
Clark, Janet Edberg, Steve Edberg, Jim Friedson, Mo Geller, Martha 
Hanner, Cliff Heindl, David Levy, Mordecai-Mark Mac Low, Al 
Metzger, Marcia Neugebauer, Glenn Orton, Elizabeth Roettger, Jim 
Scotti, David Seal, Zdenek Sekanina, Anita Sohus, Harold Weaver, 
Paul Weissman, Bob West, and Don Yeomans -- and to those who might 
have been omitted. The choice of material and the faults and flaws 
in the document obviously remain the responsibility of the author 
alone.
 
The writing and production of this material was made possible 
through the support of Jrgen Rahe and Joe Boyce, Code SL, NASA, 
and of Dan McCleese, Jet Propulsion Laboratory (JPL). For help in 
the layout and production of this booklet, on a very tight 
schedule, additional thanks go to the Design Services Group of the 
JPL Documentation Section.
 
All comments should be addressed to the author:
 
Ray L. Newburn, Jr.
Jet Propulsion Laboratory, MS 169-237
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
 
 
 
-- 
 
          _/ _/   _/ _/ _/ _/   _/ _/              David M. Seidel
         _/ _/   _/ _/     _/  _/ _/       Educational Services Specialist
        _/ _/   _/ _/ _/ _/   _/ _/           Jet Propulsion Laboratory
 _/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/    Public Education Office
_/ _/ _/ _/   _/ _/         _/ _/ _/ _/ _/         "Just say Know"

From:	US4RMC::"ASTRO%[email protected]" "Astronomy Discussion 
        List" 25-APR-1994 11:38:19.92 
To:	Multiple recipients of list ASTRO <ASTRO%[email protected]>
CC:	
Subj:	Re: Jupiter Impact

As promised, here is the telephone number for updates on the comet
impact on Jupiter.  Be warned, I have not tried this yet myself, so I
don't know what kind of information The Planetary Society is giving
out. The number is 1-800-9-WORLDS.  I hope this helps.... 

Todd K. Slisher

p.s.  Another nine year old asked me yesterday, "can we live on the
      sun"?  Now there's another _tough_ one. 

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date:         Sat, 23 Apr 1994 11:36:18 EDT
% Reply-To: Astronomy Discussion List <ASTRO%[email protected]>
% Sender: Astronomy Discussion List <ASTRO%[email protected]>
% From: Todd Slisher <D700071%[email protected]>
% Subject:      Re: Jupiter Impact
% To: Multiple recipients of list ASTRO <ASTRO%[email protected]>

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 28-APR-1994 17:22:42.83
CC:	
Subj:	Re: Observing Jupiter at Radio Wavelengths

	The following files are available via anonymous ftp on
the Univ. of Florida Dept.of Astronomy site astro.ufl.edu in the
/pub/jupiter directory.

 jupradio.txt -- Jovian Decametric Emission and the Collision of Comet
		 Shoemaker-Levy 1993e
    	         (Postscript version jupradio.ps)

 hist.ps      -- histogram of occurence probabilities of Jupiter radio
	         emission at different frequencies.

 april94.txt, may94.txt, june94.txt, july94.txt, aug94.txt 
	      -- Tables of predicted Jupiter radio storms for April
	         through August 1994. A file README.DOC is included
		 which provides an explanation of the tables.

	I hope this will be of benefit to those wishing to make radio
observations of Jupiter especially during the encounter with
Shoemaker-Levy 1993e.
				Leonard Garcia
	    
-- 
*************************************************************************
* Leonard N. Garcia              *  [email protected]                *
* Astronomy Department	         *					*
* University of Florida	         *					*
* P.O. Box 112055	         *					*
* Gainesville, FL 32611-2055     *					*
*************************************************************************

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Thu, 28 Apr 1994 14:26:31 +0700
% Errors-To: [email protected]
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: [email protected]
% Subject: Re: Observing Jupiter at Radio Wavelengths
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon"  1-MAY-1994
CC:	
Subj:	Jupiter/SL9 Radio Observations

   There's yet more information available at SEDS.LPL.Arizona.EDU! 

For those of you interested in radio observations during the SL9 impact,
Leonard Garcia of the University of Florida has made some information
avaiable.  The new files are in /pub/astro/SL9/jupradio.  This directory
will be mirrored from the University of Flordia daily.  Here the file
descriptions: 

# Directory: /pub/astro/SL9/jupradio
# Date: 5/1/94
# Radio Observation information for Jupiter

README.DOC	Explanation of predicted Jupiter radio storms tables
april94.txt 	Tables of predicted Jupiter radio storms for April 1994
aug94.txt 	Tables of predicted Jupiter radio storms for August 1994
jupradio.txt  	Jovian Decametric Emission and the Collision of SL9 and Jupiter
jupradio.ps	Postscript version of jupradio.txt
hist.ps      	Histogram of occurence probabilities of Jupiter radio
	         emission at different frequencies.
may94.txt	Tables of predicted Jupiter radio storms for May 1994
july94.txt	Tables of predicted Jupiter radio storms for July 1994
june94.txt	Tables of predicted Jupiter radio storms for June 1994

   If you have more information to add to this, it would be most appreciated.

-Chris Lewicki
[email protected]
Maintainer of SEDS.LPL.Arizona.EDU
'Legendary' Mars Observer GRS Flight Investigation Team
UA SEDS President
SEDS-USA Director of Special Projects

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Sun, 1 May 1994 15:11:51 +0700
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: Chris Lewicki <[email protected]>
% Subject: Jupiter/SL9 Radio Observations
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 11-MAY-1994 
CC:	
Subj:	Comet/Jupiter Collision FAQ

To : SL9 Mailing List Subscribers

 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *                                                                           *
 *                       Frequently Asked Questions about                    *
 *            the Collision of Comet Shoemaker-Levy 9 with Jupiter           *
 *                                                                           *
 *                         Last Updated 11-May-1994                          *
 *                            66 Days to Impact                              *
 *                                                                           *
 *     The following is a list of answers to frequently asked questions      *
 * concerning the collision of comet Shoemaker-Levy 9 with Jupiter.  Thanks  *
 * to all those who have contributed.  Contact Dan Bruton ([email protected])   *
 * or John Harper ([email protected]) with comments, additions, corrections,  *
 * etc.  A PostScript version and updates of this FAQ list are available via *
 * anonymous ftp to tamsun.tamu.edu (128.194.15.32) in the /pub/comet        *
 * directory.  To subscribe to the "Comet/Jupiter Collision Mailing List",   *
 * send mail to [email protected] (no subject) with the message: *
 *                                                                           *
 *     SUBSCRIBE SL9 Firstname Lastname                                      *
 *                                                                           *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *


RECENT CHANGES TO THIS FAQ LIST

        Question 1.3: More GIF Graphics
        Question 1.5: New Question
        Question 2.1: Updated impact times and impact locations
        Question 2.2: Radio Telescope Observations
        Question 2.3: Reflection of light from the moons
        Question 2.4: Updated orbital parameters of the comet
        Question 2.5: Location of crater chains on the Moon
        Question 2.8: Galileo's Observing Plans
        Question 2.9: More Jupiter Recorders
       Question 2.10: JPL's SL9 Book and Modified FTP and WWW Sites
          REFERENCES: New Journal Articles

GENERAL QUESTIONS

 Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 Q1.2: Who are Shoemaker and Levy?
 Q1.3: Where can I find a GIF image of this comet?
 Q1.4: What will be the effects of the collision?
 Q1.5: Can I see the effects in my telescope?

SPECIFICS

 Q2.1: What are the impact times and impact locations of the comet fragments?
 Q2.2: Can the effects of the collision be observed with radio telescopes?
 Q2.3: Will light from the explosions be reflected by any of Jupiter's moons?
 Q2.4: What are the orbital parameters of the comet?
 Q2.5: Why did the comet break apart?
 Q2.6: What are the sizes of the fragments?
 Q2.7: How long is the fragment train?
 Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?
 Q2.9: To whom can I report my observations?
 Q2.10: Where can I find more information?

REFERENCES

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

GENERAL QUESTIONS

Q1.1: Is it true that a comet will collide with Jupiter in July 1994?

     Yes, the shattered comet Shoemaker-Levy 9 (1993e) is expected to
collide with Jupiter over a 5.6 day period in July 1994.  The first of 21
comet fragments is expected to hit Jupiter on July 16, 1994 and the last on
July 22, 1994.  All components of the comet will hit on the dark farside of
Jupiter, out of sight from Earth.
     The impact of the center of the comet train is predicted to occur at a
Jupiter latitude of about -44 degrees at a point about 67 degrees east (toward
the sunrise terminator) from the midnight meridian.  These impact point
estimates from Sekanina, Chodas, and Yeomans are only 5 to 9 degrees behind
the limb of Jupiter as seen from Earth.  About 20 to 40 minutes after each
fragment hits, the impact points will rotate past the limb.  After these
points cross the limb it will take another 17 minutes before they cross the
morning terminator into sunlight.


Q1.2: Who are Shoemaker and Levy?

     Eugene and Carolyn Shoemaker and David H. Levy found the 13.8 magnitude
comet on photographic plates taken on March 24, 1993.  The photographs were
taken at Palomar Mountain in Southern California with a 0.46 meter Schmidt
camera and were examined using a stereomicroscope to reveal the comet [2,14].
James V. Scotti confirmed their discovery with the Spacewatch Telescope at
Kitt Peak in Arizona.  See [11] for more information about the discovery.


Q1.3: Where can I find a GIF image of this comet?

     GIF images can be obtained via anonymous ftp to SEDS.LPL.Arizona.EDU
(128.196.64.66) in the /pub/astro/SL9/images directory.  This site also
supports gopher.  Below is a list of the images at this site.  The files
are listed here in reverse chronological order.  Most of the images are
accompanied by a text file giving a description of the image and some of
the images are available in PostScript form.

sl90216.gif      February 16, 1994 Image from Kitt Peak (J. Scotti)
wfpclevy.gif     Photo Montage of January 24-27 Imaging of SL9 from HST
sl9hst.gif       Post-fix HST Mosaic of SL9 (Jan. 24-27)
sl90121.gif      January 21, 1994 Image from Kitt Peak (R. Jedicke)
sl9compl.gif     Six month comparison image of SL9
1993eha.gif      View of the comet from HST
1993ehb.gif      From HST, focused on the center of the train of fragments
1993esw.gif      Ground-based view of the comet
sl03302b.gif     March 30, 1993 Image from Kitt Peak (J. Scotti)
sl9_930330.gif   March 30, 1993 image of SL9, Spacewatch Telescope-J. Scotti
sl9w_930328.gif  March 28, 1993 image of SL9
shoelevy.gif     An early GIF image of SL9

   The following is a list of other collision related GIF graphics and MPEG
animations that are also available at SEDS.LPL.Arizona.EDU:

orbtrain.gif       SL9's orbit showing the length of the train
schematic2.gif     Updated diagram of fragment positions as seen from HST
schematic1.gif     Old Schematic diagram of SL9 showing positions of fragments
approach.gif       View of last 18 hours of trajectory, from Earth
earthview.gif      Full-disk view from Earth
earthviewzoom.gif  Close-up view from Earth
vgr2view.gif       Full-disk view from Voyager 2
vgr2viewzoom.gif   Close-up view of impact sites from direction of Voyager 2
galview.gif        View from Galileo
ulysview.gif       View from Ulysses
poleview.gif       View from beneath Jupiter
orbjupplane.gif    SL9's orbit projected into Jupiter's orbit plane
orbsun.gif         SL9's orbit as seen from the Sun
earthjup.gif       Jupiter-Facing Hemispheres of Earth at Impact Times of SL9
impact.gif         Graph of impact times with moon eclipses
index.gif          Mosaic of some of the images in this directory
mitwave1.gif       Frame from MIT Flow Visualization Lab. Simulation
mitwave2.gif       Frame from MIT Flow Visualization Lab. Simulation
mitwave.mpg        MIT Flow Visualization Lab. Simulation Animation
vidjv.mpg          Animation of SL9 entering Jupiter's Atmosphere
visejz.mpg         Animation of explosion produced by SL9 entering Jupiter
sl9rend.gif        Rendering 3 views of comet-Jupiter collision
sl9rend1.gif       Larger rendering comet-Jupiter from Earth
sl9rend2.gif       Larger rendering comet-Jupiter from Voyager 2
sl9rend3.gif       Larger rendering comet-Jupiter from south pole


Q1.4: What will be the effects of the collision?

     Each comet fragment will enter the atmosphere at a speed of 130,000 mph
(60 km/s).  At an altitude of 100 km above the visible cloud decks,
aerodynamic forces will overwhelm the material strength of the comet,
beginning to squeeze it and tear it apart.  Five seconds after entry, the
comet fragment will deposit its kinetic energy of around 10^28 ergs
(equivalent to around 200,000 megatons of TNT) at 100-150 km below the
cloud layer [19].  Bigger fragments will have more energy and go deeper.
     The hot (30,000 K) gas resulting from the stopped comet will explode,
forming a fireball similar to a nuclear explosion, but much larger.
The visible fireball will only rise 100 km or so above the cloudtops.
Above that height the density will drop so that it will become transparent.
The fireball material will continue to rise, reaching a height of perhaps
1000 km before falling back down to 300 km.  The fireball will spread out
over the top of the stratosphere to a radius of 2000-3000 km from the point
of impact (or so the preliminary calculations say).  The top of the resulting
shock wave will accelerate up out of the Jovian atmosphere in less than two
minutes, while the fireball will be as bright as the entire sunlit surface of
Jupiter for around 45 sec [18].  The fireball will be somewhat red, with a
characteristic temperature of 2000 K - 4000 K (slightly redder than the sun,
which is 5000 K).  Virtually all of the shocked cometary material will rise
behind the shock wave, leaving the Jovian atmosphere and then splashing back
down on top of the stratosphere at an altitude of 300 km above the clouds
[unpublished simulations by Mac Low & Zahnle].  Not much mass is involved in
this splash, so it will not be directly observable.  The splash will be
heavily enriched with cometary volatiles such as water or ammonia, and so may
contribute to significant high hazes.
        Meanwhile, the downward moving shock wave will heat the local clouds,
causing them to buoyantly rise up into the stratosphere.  This will allow
spectroscopists to attempt to directly study cloud material, a unique
opportunity to confirm theories of the composition of the Jovian clouds.
Furthermore, the downward moving shock may drive seismic waves (similar to
those from terrestrial earthquakes) that might be detected over much of the
planet by infrared telescopes in the first hour or two after each impact.
The strength of these two effects remains a topic of research.  The
disturbance of the atmosphere will drive internal gravity waves ("ripples in
a pond") outwards.  Over the days following the impact, these waves will
travel over much of the planet, yielding information on the structure of
the atmosphere if they can be observed (as yet an open question).
     The "wings" of the comet will interact with the planet before and after
the collision of the major fragments.  The so-called "wings" are defined to be
the distinct boundary along the lines extending in both directions from the
line of the major fragments; some call these 'trails'.  Sekanina, Chodas and
Yeomans have shown that the trails consist of larger debris, not dust: 5-cm
rock-sized material and bigger (boulder-sized and building-sized).  Dust gets
swept back above (north) of the trail-fragment line due to solar radiation
pressure.  The tails emanating from the major fragments consist of dust being
swept in this manner.  Only the small portion of the eastern debris trail
nearest the main fragments will actually impact Jupiter, according to the
model, with impacts starting only a week before the major impacts.  The
western debris trail, on the other hand, will impact Jupiter over a period of
months following the main impacts, with the latter portion of the trail
actually impacting on the front side of Jupiter as viewed from Earth.
        The injection of dust from the wings and tail into the Jovian system
may have several consequences.  First, the dust will absorb many of the
energetic particles that currently produce radio emissions in the Jovian
magnetosphere.  The expected decline and recovery of the radio emission may
occur over as long as several years, and yield information on the nature and
origin of the energetic particles.  Second, the dust may actually form a
second faint ring around the planet.


Q1.5: Can I see the effects in my telescope?

     One might be able to detect atmospheric changes on Jupiter using
photography or CCD imaging.  It is important, however, to observe Jupiter
for several months in advance in order to know which features are due to
impacts and which are naturally occurring.  It appears more and more likely
that most effects will be quite subtle.  Without a large ( > 15" ?) telescope
and good detector, little is likely to be seen.
     It is possible that the impacts may create a new, temporary storm at the
latitude of the impacts.  Modeling by Harrington et al. suggests this is
possible [30].  The 21 nuclei of comet Shoemaker-Levy 9 will strike just
south of the South Temperate Zone of Jupiter.  Reta Beebe of New Mexico State
points out that if the nuclei penetrate deep enough, water vapor may shoot
high into the atmosphere where it could turn into a bluish shroud over
a portion of the South Temperate Zone [31].
     Impacts of the largest fragments may create one or two features.  A spot
might develop that could be a white or dark blue nodule and would likely have
a maximum diameter of 2,000 km to 2,500 km which in a telescope would be 1" to
1.5" across.  This feature would be very short-lived with the impact site
probably returning to normal after just a few rotations of Jupiter.  A plume
might also develop that would look dark against the South Temperate Zone's
white clouds or could appear as a bright jet projected from Jupiter limb [31].
     The table below shows the approximate sizes of features that already exist
on Jupiter for comparison.

     + ==================================================================+
     |         FEATURE                            SIZE ESTIMATES         |
     + ==================================================================+
     |      Great Red Spot                       29000 by 12000 km [32]  |
     |    White Spots FA,BC,DE                   7500 by 3000 km         |
     | Shadows of Io, Europa, and Ganymede       4300, 4200, 7100 km     |
     +===================================================================+

     Below is a list of files available at tamsun.tamu.edu in the /pub/comet
directory that may be helpful in identifying features on Jupiter:

  may1994.transit   Transit Times for Red Spot and White Spots for May 1994
  may1994.moons     Jovian Moon events for May 1994 (Shadows, Eclipses, etc.)
  meridian.bas      PC BASIC Program, System I & II Long. for Central Meridian
  redspot.bas       PC BASIC Program; Location of GRS; System I and II Long.
  redtran.bas       PC BASIC Program; Transit times of the GRS
  jupe.description  Description of a PC program showing features of Jupiter


* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *


SPECIFICS

Q2.1: What are the impact times and impact locations of the comet fragments?

     The following table gives the latest impact predictions as of
April 23, 1994.  All the information in the table except for the System II
Longitudes was provided P.W. Chodas, D.K. Yeomans and Z. Sekanina
(JPL/Caltech), P.D. Nicholson (Cornell).

                      IMPACT TIMES AND LOCATIONS (July 1994)
  +========================================================================+
  |                 UT Date    Jovicentric   Meridian   E-J-F   System II  |
  |                of Impact     Latitude     Angle     Angle   Longitude  |
  | Fragment       dy  hr mn      (deg)       (deg)     (deg)     (deg)    |
  +========================================================================+
  |  A = 21   July 16  20: 1     -43.31       65.09     98.27      118     |
  |  B = 20   July 17   3:11     -43.34       65.42     98.02       17     |
  |  C = 19   July 17   7: 3     -43.41       65.59     97.88      157     |
  |  D = 18   July 17  11:58     -43.47       65.81     97.70      335     |
  |  E = 17   July 17  14:56     -43.56       65.40     97.96       83     |
  |  F = 16   July 18   2:37     -45.06       64.83     98.03      148     |
  |  G = 15   July 18   7:35     -43.71       66.81     96.91      326     |
  |  H = 14   July 18  19:23     -43.78       66.57     97.07       34     |
  |  J = 13    Disappeared                                                 |
  |  K = 12   July 19  10:40     -43.94       68.25     95.83      226     |
  |  L = 11   July 19  21:55     -44.00       67.76     96.17      274     |
  |  M = 10    Disappeared                                                 |
  |  N =  9   July 20  10:25     -44.97       65.87     97.30       10     |
  |  P2= 8b   July 20  15:29     -45.10       66.46     96.86      193     |
  |  P1= 8a    Disappeared                                                 |
  |  Q2= 7b   July 20  19:27     -44.38       68.89     95.29      334     |
  |  Q1= 7a   July 20  19:54     -44.10       69.31     95.04      350     |
  |  R =  6   July 21   5:41     -44.20       69.61     94.80      344     |
  |  S =  5   July 21  15:24     -44.18       70.20     94.38      336     |
  |  T =  4   July 21  18:30     -44.23       70.30     94.30       88     |
  |  U =  3   July 21  21:43     -44.26       70.44     94.19      205     |
  |  V =  2   July 22   4:48     -44.27       70.75     93.96      101     |
  |  W =  1   July 22   8:19     -44.21       71.05     93.77      229     |
  +========================================================================+
  | Approximate                                                            |
  | Uncertainty       22 min       0.11        0.62      0.44       14     |
  |  (1-sigma)                                                             |
  +========================================================================+

Table Notes:

*  The 21 major fragments are denoted A through W in order of impact, with
   letters I and O not used.  It is apparent from the HST image taken in late
   January that that P and Q each consist of two components.  Impact times
   for fragments J, M, and P1 are not included in the table because they have
   disappeared: they are not visible in the HST image taken in March 1994

*  The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

*  The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.

*  Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact.

*  The impact times above include the light time to the Earth (~ 43 minutes).

*  The angle of incidence of the impacts is between 41 and 42 degrees
   for all the fragments.

*  See "impacts.940423" at SEDS.LPL.Arizona.EDU in the /pub/astro/SL9/info
   directory for more details about these predictions.

     The following are the 1-sigma (uncertainty) predictions for the
fragment impact times:

          on March 1         -  30 min
          on May 1           -  24 min
          on June 1          -  16 min
          on July 1          -  10 min
          on July 15         -   6 min
          at impact - 18 hr  -   3 min

The time between impacts is thought to be known with more certainty than the
actual impact times.  This means that if somehow the impact time of the first
fragment can be measured experimentally, then impact times of the fragments
that follow can be predicted with more accuracy.


Q2.2: Can the effects of the collision be observed with radio telescopes?

     The cutoff of radio emissions due to the entry of cometary dust into the
Jovian magnetosphere during the weeks around impact may be clear enough to be
detected by small radio telescopes.  Furthermore, impacts may be directly
detectable in radio frequencies.  Some suggest to listen in on 15-30 MHz during
the comet impact.  So it appears that one could use the same antenna for both
the Jupiter/Io phenomenon and the Jupiter/comet impact.  There is an article
in Sky & Telescope magazine which explains how to build a simple antenna for
observing the Jupiter/Io interaction [4,24,25].  This antenna is less
directional than a dipole or long-wire antenna.
     For those interested in radio observations during the SL9 impact, Leonard
Garcia of the University of Florida has made some information available.  The
following files are available via anonymous ftp on the University of Florida,
Department of Astronomy site astro.ufl.edu in the/pub/jupiter directory:

  README.DOC      Explanation of predicted Jupiter radio storms tables
  jupradio.txt    Jovian Decametric Emission and the SL9/Jupiter Collision
  jupradio.ps     Postscript version of jupradio.txt
  hist.ps         Histogram of occurrence probabilities of Jupiter radio
                        emission at different frequencies.
  may94.txt       Tables of predicted Jupiter radio storms for May 1994
  june94.txt      Tables of predicted Jupiter radio storms for June 1994
  july94.txt      Tables of predicted Jupiter radio storms for July 1994


Q2.3: Will light from the explosions be reflected by any of Jupiter's moons?

     One may be able to witness the collisions indirectly by monitoring the
brightness of the Galilean moons that may be behind Jupiter as seen from
Earth.  One could monitor the moons using a photometer, a CCD camera, or a
video camera.  However, current calculations suggest that the brightenings may
be as little as 0.05% of the sunlit brightness of the moon [18].  If a moon
can be caught in eclipse but visible from the earth during an impact, prospects
will improve significantly.  According to current predictions, the only impact
certain to occur during a satellite eclipse is K=12 with Europa eclipsed.
However, H=14 and W=1 impact only about 2 sigma after Io emerges from eclipse
at longitude 20 deg, and B=20, E=17 and F=16 impact 0.5-2 sigma after Amalthea
emerges from eclipse at longitude 34 deg.
     The following files contain information concerning the reflection of light
by Jupiter's moons and are available at SEDS.LPL.Arizona.EDU :

   impact_24apr.ps   PostScript Plot of impact times at satellite availability
   jsat8.export      Jovian satellite locations (condensed version)
   jsat8. full       Jovian satellite locations (full version)
   impacts.940423    More on Jovian Satellites
   galsat51.zip      MSDOS Program that Displays relative positions of
                      Jupiter's Moons during times of impact


Q2.4: What are the orbital parameters of the comet?

   Comet Shoemaker-Levy 9 is actually orbiting Jupiter, which is most unusual:
comets usually just orbit the Sun.  Only two comets have ever been known to
orbit a planet (Jupiter in both cases), and this was inferred in both cases by
extrapolating their motion backwards to a time before they were discovered.
S-L 9 is the first comet observed while orbiting a planet.  Shoemaker-Levy 9's
previous closest approach to Jupiter (when it broke up) was on July 7, 1992;
the distance from the center of Jupiter was about 96,000 km, or about 1.3
Jupiter radii.  The comet is thought to have reached apojove (farthest from
Jupiter) on July 14, 1993 at a distance of about 0.33 Astronomical Units from
Jupiter's center.  The orbit is very elliptical, with an eccentricity of over
0.995.  Computations by Paul Chodas, Zdenek Sekanina, and Don Yeomans, suggest
that the comet has been orbiting Jupiter for 20 years or more, but these
backward extrapolations of motion are highly uncertain.  See "elements.940422"
and "ephemeris.940422" at SEDS.LPL.Arizona.EDU for more information.


Q2.5: Why did the comet break apart?

     The comet broke apart due to tidal forces on its closest approach to
Jupiter (perijove) on July 7, 1992 when it passed within the theoretical
Roche limit of Jupiter.  Shoemaker-Levy 9 is not the first comet observed
to break apart.  Comet West shattered in 1976 near the Sun [3].  Astronomers
believe that in 1886 Comet Brooks 2 was ripped apart by tidal forces near
Jupiter [2].
     Furthermore, images of Callisto and Ganymede show crater chains which may
have resulted from the impact of a shattered comet similar to Shoemaker-Levy
9 [3,17].  The satellite with the best example of aligned craters is Callisto
with 13 crater chains.  There are three crater chains on Ganymede.  These
were first thought to be from basin ejecta; in other words secondary craters.
See [27] for more photos of crater chains.
     There are also a few examples of crater chains on our Moon.  Jay Melosh
and Ewen Whitaker have identified 2 possible crater chains on the moon which
would be generated by near-Earth tidal breakup.  One is called the "Davy
chain" and it is very tiny but shows up as a small chain of craters aligned
back toward Ptolemaeus.  In near opposition images, it appears as a high
albedo line; in high phase angle images, you can see the craters themselves.
The second is between Almanon and Tacitus and is larger (comparable to the
Ganymede and Callisto chains in size and length).


Q2.6: What are the sizes of the fragments?

     Using measurements of the length of the train of fragments and a model
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the
parent nucleus of the comet (before breakup) was only about 2 km across [13].
This would imply that the individual fragments are no larger than about 500
meters across.  Images of the comet taken with the Hubble Space Telescope in
July 1993 indicate that the fragments are 3-4 km in diameter (3-4 km is an
upper limit based on their brightness).  A more elaborate tidal disruption
model by Sekanina, Chodas and Yeomans [20] predicts that the original comet
nucleus was at least 10 km in diameter.  This means the largest fragments
could be 3-4 km across, a size consistent with estimates derived from the
Hubble Space Telescope's July 1993 observations.
     The new images, taken with the Hubble telescope's new Wide Field and
Planetary Camera-II instrument on January 24-27, 1994, have given us an even
clearer view of this fascinating object, which should allow a refinement of
the size estimates.  In addition, the new images show strong evidence for
continuing fragmentation of some of the remaining nuclei, which will be
monitored by the Hubble telescope over the next several months.


Q2.7: How long is the fragment train?

     The angular length of the train was about 51 arcseconds in March 1993 [2].
The length of the train then was about one half the Earth-Moon distance.
In the day just prior to impact, the fragment train will stretch across 20
arcminutes of the sky, more that half the Moon's angular diameter.  This
translates to a physical length of about 5 million kilometers.  The train
expands in length due to differential orbital motion between the first and
last fragments.  Below is a table with data on train length based on Sekanina,
Chodas, and Yeomans's tidal disruption model:

           +=============================================+
           |    Date    Angular Length  Physical Length  |
           |               (arcsec)          (km)        |
           +=============================================+
           |  93 Mar 25       49            158,000      |
           |     Jul  1       67            265,000      |
           |  94 Jan  1      131            584,000      |
           |     Feb  1      161            669,000      |
           |     Mar  1      200            762,000      |
           |     Apr  1      255            893,000      |
           |     May  1      319          1,070,000      |
           |     Jun  1      400          1,366,000      |
           |     Jul  1      563          2,059,000      |
           |     Jul 15      944          3,593,000      |
           |    Impact A    1286          4,907,000      |
           +=============================================+


Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?

     The Hubble Space Telescope, like earthlings, will not be able to see the
collisions but will be able to monitor atmospheric changes on Jupiter.  The new
impact points are more favorable for viewing from spacecraft: it can now be
stated with certainty that the impacts will all be visible to Galileo, and now
at least some impacts will be visible to Ulysses.  Although Ulysses does not
have a camera, it will monitor the impacts at radio wavelengths.
        Galileo will get a direct view of the impacts rather than the grazing
limb view previously expected.  The Ida image data playback is scheduled to
end at the end of June, so there should be no tape recorder conflicts with
observing the comet fragments colliding with Jupiter.  The problem is how to
get the most data played back when Galileo will only be transmitting at 10 bps.
One solution is to have both Ulysses and Galileo record the event and and store
the data on their respective tape recorders.  Ulysses observations of radio
emissions data will be played back first and will at least give the time of
each comet fragment impact.  Using this information, data can be selectively
played back from Galileo's tape recorder.  From Galileo's perspective, Jupiter
will be 60 pixels wide and the impacts will only show up at about 1 pixel,
but valuable science data can still collected in the visible and IR spectrum
along with radio wave emissions from the impacts.  (See "galileo.txt" at
SEDS.LPL.Arizona.EDU for more information.)
     The impact points are also viewable by both Voyager spacecraft, especially
Voyager 2.  Jupiter will appear as 2.5 pixels from Voyager 2's viewpoint and
2.0 pixels for Voyager 1.  However, it is doubtful that the Voyagers will
image the impacts because the onboard software that controls the cameras has
been deleted, and there is insufficient time to restore and test the camera
software.  The only Voyager instruments likely to observe the impacts are the
ultraviolet spectrometer and planetary radio astronomy instrument.  Voyager 1
will be 52 AU from Jupiter and will have a near-limb observation viewpoint.
Voyager 2 will be in a better position to view the collision from a perspective
of looking directly down on the impacts, and it is also closer at 41 AU.


Q2.9: To whom can I report my observations?

     Observation forms by Steve Lucas are available via ftp at oak.oakland.edu
in the /pub/msdos/astrnomy directory.  These forms also contain addresses of
"Jupiter Watch Program" section leaders.  "jupcom02.zip" contains Microsoft
Write files.  The Association of Lunar and Planetary Observers (ALPO) will also
distribute a handbook to interested observers.  The handbook "The Great Crash
of 1994" is available for $10 by

                        ALPO Jupiter Recorder
                        Phillip W. Budine
                        R.D. 3, Box 145C
                        Walton, NY 13856 U.S.A.

The cost includes printing, postage and handling.
     John Rogers, the Jupiter Section Director for the British Astronomical
Association, will be collecting data from regular amateur Jupiter observers
in Britain and worldwide.  He can be reached via email ([email protected])
or fax (UK [223] 333840).  For other addresses see page 44 of the January 1994
issue of Sky & Telescope magazine [14].


Q2.10: Where can I find more information?

     The SL9 educator's book put out by JPL is in the /pub/astro/SL9/EDUCATOR
directory of SEDS.LPL.Arizona.edu.  See also "factsheet.txt" or "factsheet.ps"
in the /pub/astro/SL9/info directory of this site.
     There are two technical papers [18,19] on the atmospheric consequences
of the explosions available via anonymous ftp from oddjob.uchicago.edu in the
pub/jupiter directory.  The paper and figures are available in UNIX compressed
PostScript format; a couple of the computational figures are also available
in TIFF format.
     SEDS (Students for the Exploration and Development of Space) has set up
an anonymous account which allows you to use "lynx" - a VT100 WWW browser.
To access this service, telnet to SEDS.LPL.Arizona.EDU and login as "www"
(no password required).  This will place you at the SEDS home page, from which
you can select Shoemaker-Levy 9.  A similar "gopher" interface is available at
the same site.  Just login as "gopher".
     Below is a list of FTP and WWW sites with SL9 information:

===============================================================================
   FTP SITE NAME       IP ADDRESS       DIRECTORY              CONTENTS
===============================================================================
SEDS.LPL.Arizona.EDU (128.196.64.66)  /pub/astro/SL9         Images & Info
oddjob.uchicago.edu                   /pub/jupiter           Article & figures
jplinfo.jpl.nasa.gov (137.78.104.2)   /news and /images      Images
ftp.cicb.fr          (129.20.128.34)  /pub/Images/ASTRO/hst  Images
tamsun.tamu.edu      (128.194.15.32)  /pub/comet             Images & Info

===============================================================================
     WORLD WIDE WEB SITES                                           CONTENTS
===============================================================================
http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html      Info & Images
http://seds.lpl.arizona.edu/sl9/sl9.html                          Images & Info
http://pscinfo.psc.edu/research/user_research/user_research.html  Animations


REFERENCES

[1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
[2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
      page 38-39.
[3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
      chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
[4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
[5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
[6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
[7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
[8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
      September 1993, page 18.
[9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
[10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
[11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
[12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
      of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
[13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
      Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
[14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
      January 1994, page 40-44.
[15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
[16] "AstroNews", Astronomy, January 1994, page 19.
[17] "AstroNews", Astronomy, February 1994, page 16.
[18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
      Comet Shoemaker Levy 9", submitted to Icarus October 29, 1993.
[19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
      Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
      submitted to Science on 10 February 1994.
[20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the
      Appearance of Periodic Comet Shoemaker-Levy 9", submitted to Astronomical
      Journal, November 1993.
[21] "On a collision Course with Jupiter", Mercury, Nov-Dec 1993, page 15-16.
[22] "Timing the Crash", Sky & Telescope, February 1994, page 11.
[23] "Capturing Jupiter on Video" Sky & Telescope, September 1993, page 102.
[24] North, Gerald, "Advanced Amateur Astronomy", page 296-298, (1991).
[25] "Backyard Radio Astronomy", Astronomy, March 1983, page 75-77.
[26] Harrington, J., R. P. LeBeau, K. A. Backes, and T. E. Dowling,
     "Dynamic response of Jupiter's atmosphere to the impact of comet
     Shoemaker-Levy 9" Nature 368: 525-527 (1994).
[27] David Morrison, "Satellites of Jupiter", page 392, (1982).
[28] Weaver, H. A., P. D. Feldman, M. F. A'Hearn, C. Arpigny, R. A. Brown,
     E. F. Helin, D. H. Levy, B. G. Marsden, K. J. Meech, S. M. Larson,
     K. S. Knoll, J. V. Scotti, Z. Sekanina, C. S. Shoemaker, E. M. Shoemaker,
     T. E. Smith, A. D. Storrs, D. K. Yeomans, and B. Zellner,
     "Hubble Space Telescope Observations of Comet P/Shoemaker-Levy 9 (1993e)."
     Science 263, page 787-791, (1994).
[29] Duffy, T.S., W.L. Vos, C.S. Zha, H.K. Mao, and R.J. Hemley.  "Sound
     Velocities in Dense Hydrogen and the Interior of Jupiter"  Science 263,
     page 1590-1593, (1994).
[30] Harrington, J., R. P. LeBeau, K. A. Backes, & T. E. Dowling, "Dynamic
     response of Jupiter's atmosphere to the impact of comet P/Shoemaker-
     Levy 9", Nature 368, page 525-527, April 7, 1994.
[31] Olivares, Jose, "Jupiter's Magnificent Show", Astronomy, April 1994,
     page 74-79.
[32] Schmude, Richard W., "Observations of Jupiter During the 1989-90
     Apparition", The Strolling Astronomer: J.A.L.P.O., Vol. 35, No. 3.,
     September 1991.

ACKNOWLEDGMENTS

     Thanks to Ross Smith for starting a FAQ and to all those who have
contributed :  Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke, Rik Hill,
Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke, David H. Levy,
Eugene and Carolyn Shoemaker, Jim Scotti, Richard A. Schumacher,
Louis A. D'Amario, John McDonald, Michael Moroney, Byron Han, Wayne Hayes,
David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki, Jeffrey A Foust,
Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina, Don Yeomans,
Richard Schmude, Lenny Abbey, Chris Lewicki, the Students for the Exploration
and Development of Space (SEDS), David A. Seal, and Leonard Garcia.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .


% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Wed, 11 May 1994 14:06:52 +0700
% Message-Id: <[email protected]>
% Originator: [email protected]
% Sender: [email protected]
% From: [email protected]
% Subject: Comet/Jupiter Collision FAQ
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

    	The May 23 issue of Time magazine has the comet SL-9 impact
    on Jupiter as its cover story, complete with a warning to Earth
    about similar incidents.  Have to tie it into humanity somehow.
    
    	Larry
    

From:	VERGA::US4RMC::"[email protected]" 24-MAY-1994 16:13:23.96
To:	Multiple recipients of list <[email protected]>
CC:	
Subj:	DOME-L digest 164

			    DOME-L Digest 164

Topics covered in this issue include:

  1) Covering P/SL9-Jupiter fr. yr. Pltm. - Part 1 of 4
	by Robert Landis <[email protected]>
  2) P/SL9-Jupiter fr. yr. Pltm - Part 2 of 4
	by Robert Landis <[email protected]>
  3) P/SL9-Jupiter fr. yr. Pltm - Part 3 of 4
	by Robert Landis <[email protected]>
  4) P/SL9-Jupiter fr. yr. Pltm - Part 4 of 4
	by Robert Landis <[email protected]>

----------------------------------------------------------------------

Topic No. 1

Date: Tue, 24 May 1994 15:47:18 -0400 (EDT)
From: Robert Landis <[email protected]>
To: "Planetarian's Digest" <[email protected]>
Subject: Covering P/SL9-Jupiter fr. yr. Pltm. - Part 1 of 4
Message-ID: <[email protected]>

Due to the nature of the overwhelming requests I received at MAPS last
week, I'm making this paper available on the Internet.  Note it is sans
illustrations.  It will be posted to dome-l and sci.astro.planetarium.
Good luck!

++Rob Landis, STScI
  Moving Targets Group

email:  [email protected]


				MAPS Conference
		            Southworth Planetarium
		             Portland, ME  04103

	                       18 - 21 May 1994


		"Comet P/Shoemaker-Levy's Collision with Jupiter:  
            Covering HST's Planned Observations from Your Planetarium"


Abstract:  Comet Shoemaker-Levy 9 (1993e) was discovered in March
1993. Early ground-based observations indicated the comet had
fragmented into several pieces.  The comet is in a highly inclined,
elliptical orbit around Jupiter.  P/Shoemaker-Levy 9 was tidally
ripped apart during peri-Jove in July 1992. The Hubble Space Telescope
has provided the most detailed look to date and resolved 20 separate
nuclei.  The nuclei are expected to slam into Jupiter over a five-day
period beginning on 16 July 1994.  The total energy of the collisions
will be equivalent to 100 million megatons of TNT (more than 10,000
times the total destructive power of the world's nuclear arsenal at
the height of the Cold War).  An armada of spacecraft will observe the
event:  Voyager 2, Galileo, IUE, Ulysses, and the Hubble Space
Telescope. HST will be the astronomical instrument of choice to
observe P/SL9, and the after effects of the energy imparted into the
Jovian atmosphere.  NASA Select television may provide planetarium
patrons with a ringside seat of the unfolding drama at Jupiter. 


Introduction

	The author and Steve Fentress (Strasenburgh Planetarium) had
remarkable success covering the Voyager 2/Neptune encounter during
August 1989 using exist- ing NASA video and still images.  No special
effects were needed -- nor used -- to bring Voyager 2's odyssey to the
Upstate New York community.  During the first week of December 1993,
several major planetaria achieved similar success in their coverage of
the first servicing mission to the Hubble Space Telescope .  Another
opportunity for planetaria to cover fast-breaking astronomical and
space science news awaits this summer as P/Shoemaker-Levy 9 collides
with Jupiter.  What follows is background material on the HST, the
comet, Jupiter, and the planned observations of the upcoming
collisions. 

	Planetaria and science centers worldwide have a unique
opportunity to be involved in the understanding and exploration of our
solar system when you participate in the P/Shoemaker-Levy collision
with Jupiter.  Public interest in your program will have been greatly
stimulated before and during the series of collisions by daily
television broadcasts, newspapers, and magazines.  In certain areas of
the nation, local cable companies will be carrying the NASA Select
signal to further stimulate interest in the event. 

	We at the Space Telescope Science Institute and National Aeronautics 
and Space Administration anticipate that the public interest will be extremely 
high and that you may expect large attendances at your location.

	Never before in modern times has a collision between two solar system 
bodies been observed.  The instrument of choice to observe this unique event 
will be the Hubble Space Telescope. 
 
		The Hubble Space Telescope:  Planned Observations of 
		Periodic Comet Shoemaker-Levy 9  (1993e) and Jupiter

	The Hubble Space Telescope is a NASA project with
international coopera- tion from the European Space Agency (ESA).  HST
is a 2.4-meter reflecting telescope which was deployed in low-Earth
orbit (600 kilometers) by the crew of the space shuttle Discovery
(STS-31) on 25 April 1990. 

	Responsibility for conducting and coordinating the science
operations of the Hubble Space Telescope rests with the Space
Telescope Science Institute (STScI) on the Johns Hopkins University
Homewood Campus in Baltimore, Maryland. STScI is operated for NASA by
the Association of University for Research in Astronomy, Incorporated
(AURA). 

	HST's current complement of science instruments include two
cameras, two spectrographs, and fine guidance sensors (primarily used
for astrometric observations).  Because of HST's location above the
Earth's atmosphere, these science instruments can produce high
resolution images of astronomical objects. Ground-based telescopes can
seldom provide resolution better than 1.0 arc-seconds, except
momentarily under the very best observing conditions.  HST's
resolution is about 10 times better, or 0.1 arc-seconds. 

	It is generally expected that nearly every observatory in the
world will be observing events associated with Comet Shoemaker-Levy's
impacts on Jupiter. Most observatories are setting aside time and
resources but delaying detailed planning until the last possible
minute in order to optimize their observations based on the latest
theoretical predictions and the latest observations of the cometary
properties.  Having the advantage of being above the Earth's turbulent
atmosphere, HST is the astronomical spacecraft of choice to observe
the unfolding drama of Comet P/Shoemaker-Levy 9 collision with
Jupiter.  Other spacecraft to observe the event include the
International Ultraviolet Explorer (IUE), Extreme Ultraviolet
Explorer, Galileo, Voyager 2, Ulysses, and possibly others. 

	From 16 July through 22 July 1994, pieces of an object designated as
Comet P/Shoemaker-Levy 9 will collide with Jupiter, and may have observable 
effects on Jupiter's atmosphere, rings, satellites, and magnetosphere. Since 
this is the first collision of two solar system bodies ever to be observed,
there is large uncertainty about the effects of the impact.  Shoemaker-Levy 9 
consists of nearly 20 discernible bodies with diameters estimated at 2 to 4 
kilometers (km), depending on method of estimation and assumptions about the 
nature of the bodies, a dust coma surrounding these bodies, and an unknown
number of smaller bodies.  All the large bodies and much of the dust will be
involved in the energetic, high-velocity impact with Jupiter.   

	The Hubble Space Telescope has the capability of obtaining the
highest resolution images of all observations and will continue to
image the morphology and evolution of the comet until days before
first fragments of the comet impact with Jupiter.  HST's impressive
array of science instruments will study Jupiter, P/Shoemaker-Levy 9,
and the Jovian environs before, during, and after the collision
events.   The objective of these observations is to better cons- train
astrometry, impact times,  fragment sizes, study the near-fragment
region and perform deep spectroscopy on the comet.  During the
collision events it is hoped that the HST will be able to image the
fireball at the limb, and after collisions the atmosphere, rings,
satellites, and magnetosphere will be monitored for changes caused by
the collision.  The HST will devote approxi- mately 18 hours of time
with the Wide Field/Planetary Camera (WF/PC -- pronounced "wif-pik"). 
The disk of Jupiter will be about 150 pixels across in the images, a
resolution of about 1000 km/pixel. 

	The HST program that has been approved consists of 112 orbits of obser-
vations of both the comet and Jupiter.  The observations will be made by six 
different teams.


Table 1: Science Observation Team (SOT) Principal Investigators for 
         the HST Jupiter Campaign.


Principal 	Science 	Target		Science Objectives
Investigator	Instrument
========================================================================
________________________________________________________________________
Hal Weaver	WFPC+FOS 	SL9		morphology, breakup,
(STScI) 					OH emission
________________________________________________________________________
Heidi Hammel    WFPC            Jupiter  	seismic/gravity waves
(MIT)                                    	clouds and wind fields
________________________________________________________________________
Keith Noll      FOS+HRS       	Jupiter  	composition changes 
(STScI)						at impact sites
________________________________________________________________________
Melissa McGrath FOS+HRS       	magnetosphere   dust contamination
(STScI)                                         of magnetosphere
________________________________________________________________________
John Clarke     WFPC+FOC      	Jupiter   	UV imaging of clouds 
(U Mich)                                        and aurorae
________________________________________________________________________
Bob West        WFPC            Jupiter    	stratospheric haze
(JPL)
________________________________________________________________________

Table 2:  HST Jupiter/Shoemaker-Levy Campaign Programs

o UV Observations of the Impact of Comet SL9 with Jupiter
o A Search for SiO in Jupiter's Atmosphere
o Abdundances of Stratospheric Gas Species from Jovian Impact Events
o SL9's Impact on the Jovian Magnetosphere
o Observations of Io's and Europa's Regions of Jovian Magnetosphere for
  Cometary Products
o Dynamical Parameters of Jupiter's Troposphere and Stratosphere
o HST Observations of the SL9 Impacts on Jupiter's Atmosphere
o Comparison of Meterological Models with HST Images
o FUV Imaging of Jupiter's Upper Atmosphere
o Auroral Signature of the Interaction of SL9 with the Jovian Magnetosphere
o HST Imaging Investigation of SL9
o Cometary Particles as Tracers of Jupiter's Stratospheric Circulation

A bit more than 1/3 of the observations will be of the comet with the
remainder focused on Jupiter and environs.  The comet observations
have already begun, the first being made in late January.  The next
will be in late March, with three more observations spaced in time up
to mid-July,  just before impact.  The Jupiter observations begin the
week before impact.  The impact week has many observations, and
followup observations continue sporadically until late August. Details
of the observing program are being finalized. 

		###next:  Background on P/SL9 and Jupiter###


------------------------------

Topic No. 2

Date: Tue, 24 May 1994 15:47:39 -0400 (EDT)
From: Robert Landis <[email protected]>
To: "Planetarian's Digest" <[email protected]>
Subject: P/SL9-Jupiter fr. yr. Pltm - Part 2 of 4
Message-ID: <[email protected]>

		Some Background on Comet Shoemaker-Levy 9 and Jupiter

	A comet, already split into many pieces, will strike the
planet Jupiter in the third week of July of 1994.  It is an event of
tremendous scientific interest but, unfortunately, one which is likely
to be unobservable by the general public. Nevertheless, it is a unique
phenomenon and secondary effects of the impacts will be sought after
by both amateur and professional astronomers. 

				    Significance

	The impact of Comet Shoemaker-Levy 9 onto Jupiter represents
the first time in human history that people have discovered a body in
the sky and been able to predict its impact on a planet more than
seconds in advance.  The impact will deliver more energy to Jupiter
than the largest nuclear warheads ever built, and up to a significant
percentage of the energy delivered by the impact which is generally
thought to have caused the extinction of the dinosaurs on Earth,
roughly 65 million years ago. 

				      History

	Periodic Comet Shoemaker-Levy 9 (1993e) is the ninth short-period comet
discovered by husband and wife scientific team of Carolyn and Gene Shoemaker 
and amatuer astronomer David Levy.  The comet was photographically discovered 
on 24 March 1993 with the 0.46-meter Schmidt telescope at Mt. Palomar.  On the
original image it appeared 'squashed'.  Subsequent confirmation photographs at 
a larger scale taken by Jim Scotti with the Spacewatch telescope on Kitt Peak
showed that the comet was split into many separate fragments.  Scotti reported
at least five condensations in a very long, narrow train approximately 47
arc-seconds in length and and about 11 arc-seconds in width, with dust trails
extending from either end of the nuclear train.  Its discovery was a
serendipitous product of their continuing search for near-Earth objects,
Near-Earth objects are bodies whose orbits come nearer to the Sun than that 
of Earth and hence have some potential for collisions with Earth. 

	The International Astronomical Union's Central Bureau for Astronomical
Telegrams immediately issued a circular, announcing the discovery of the new
comet.  The comet's brightness was reported as about 14th magnitude, more than 
a thousand times too faint to be seen with the naked eye.  Bureau director Brian
G. Marsden noted that the comet was some 4 degrees from Jupiter and that its
motion suggested that it could be near Jupiter's distance from the Sun.

                  
	Before the end of March it was realized that the comet had made a very 
close approach to Jupiter in mid-1992 and at the beginning of April, after 
sufficient observations had been made to determine the orbit more reliably, 
Brian Marsden found that the comet is in orbit around Jupiter. 

	By late May it became apparent that the comet was likely to
impact Jupiter in 1994.  Since then, the comet has been the subject of
intensive study.  Searches of archival photographs have identified
pre-discovery images of the comet from earlier in March 1993 but
searches for even earlier images have been unsuccessful. 

				Cometary Orbit

	According to the most recent computations, the comet passed
less than 1/3 of a Jovian radius (120,000 km) above the clouds of
Jupiter late on 7 July 1992 (UT).  The individual fragments separated
from each other 1-1/2 hours after closest approach to Jupiter and they
are all in orbit around Jupiter with an orbital period of about two
years.  Calculations of the orbit prior to 7 July 1992 are very
uncertain but it seems very likely that the comet was previously in
orbit around Jupiter for two decades or more.  Ed Bowell and Lawrence
Wasserman of the Lowell Observatory have integrated the best currently
available orbit for P/Shoemaker-Levy 9  in a heliocentric reference
frame, and noted that the calcula- tions put the "comet" in a
"Jupiter-grazing" orbit before about 1966.  Wasserman and Bowell's
possible Jupiter close approaches are in 2-, 3-, and 4-year intervals.

Table 3:  Possible Close Approaches of 1993e with Jupiter

	       Distance			  Year/Month/Date

	1993e 0.08963 AU from Jupiter on 1971   4   26.0       	  	
	1993e 0.06864 AU from Jupiter on 1975   4   26.8 
	1993e 0.07000 AU from Jupiter on 1977   5    7.0 
	1993e 0.11896 AU from Jupiter on 1980   2    1.8                       
	1993e 0.12453 AU from Jupiter on 1982   5   26.0                        
	1993e 0.11937 AU from Jupiter on 1984  10    4.5
	1993e 0.07031 AU from Jupiter on 1987   7   12.4               
	1993e 0.06090 AU from Jupiter on 1989   8    2.5                    
	1993e 0.00072 AU from Jupiter on 1992   7    8.0                       
	1993e         Impacts Jupiter on 1994   7   16.8

     
Because the orbit takes the comet nearly 1/3 of an astronomical unit
(30 million miles) from Jupiter, the sun causes significant changes in
the orbit.  Thus, when the comet again comes close to Jupiter in 1994
it will actually impact the planet, moving almost due northward at 60
km/sec aimed at a point only halfway from the center of Jupiter to the
visible clouds. 

	All fragments will hit Jupiter in the southern hemisphere, at
latitudes near 45 degrees south, between 16 and 22 July 1994,
approaching the atmosphere at an angle roughly 45 degrees from the
vertical.  The times of the impacts are now known to within roughly 20
minutes,  but continuing observations leading up to the impacts will
refine the precision of the predictions.  The impacts will occur on
the back side of Jupiter as seen from Earth; that is, out of direct
view from the Earth (this also means that the comet will strike on
Jupiter's nightside).  This area will be close to the limb of Jupiter
and will be carried by Jupiter's rotation to the front,  illuminated
side less than half an hour after the impact.  The grains ahead of and
behind the comet will impact Jupiter over a period of four months,
centered on the time of the impacts of the major fragments.  The
grains in the tail of the comet will pass behind Jupiter and remain in
orbit around the planet. 

				The Nature of the Comet

	The exact number of large fragments is not certain since the
best images show hints that some of the larger fragments may be
multiple.  At least 21 major fragments were originally identified.  No
observations are capable of resolving the individual fragments to show
the solid nuclei.  Images with the Hubble Space Telescope suggest that
there are discrete, solid nuclei in each of the largest fragments
which, although not spatially resolved, produce a single, bright pixel
that stands out above the surrounding coma of grains.  Reasonable
assumptions about the spatial distribution of the grains and about the
reflectivity of the nuclei imply sizes of 2 to 4 km (diameter) for
each of the 11 brightest nuclei. Because of the uncertainties in these
assumptions, the actual sizes are very uncertain and there is a small
but not negligible possibility that the peak in the brightness at each
fragment is due not to a nucleus but to a dense cloud of grains. 

	No outgassing has been detected from the comet but
calculations of the expected amount of outgassing suggest that more
sensitive observations are needed because most ices vaporize so slowly
at Jupiter's distance from the sun.  The spatial distribution of dust
suggests that the material ahead of and behind the major fragments in
the orbit are likely large particles from the size of sand up to
boulders.  The particles in the tail are very small, not much larger
than the wavelength of light. The brightnesses of the major fragments
were observed to change by factors up to 1.7 between March and July
1993, although some became brighter while others became fainter.  This
suggests intermittent release of gas and grains from the nuclei. 

	Studies of the dynamics of the breakup suggest that the
structural strength of the parent body was very low and that the
parent body had a diameter of order 5 km.  This is somewhat smaller
than one would expect from putting all the observed fragments back
together but the uncertainties in both estimates are large enough that
there is no inconsistency. 

				Crater Chains

	Although none of the fragments will hit any of Jupiter's large
satellites, Voyager data indicate that tidally split comets have hit
the Galilean satellites in the past.  Until the discovery of Comet
P/Shoemaker-Levy 9, the strikingly linear crater chains on Callisto
and Ganymede had remained unexplained.  It is quite likely that these
crater chains were formed by comets similar to P/SL9. 

	The longest of the chains, is 620 km long and comprises 25
craters.  The first interpretation hinted that these were secondary
impact chains, formed by material ejected from large basins -- very
much akin to the Earth's Moon.  The Callisto chains are much
straighter and more uniform than most secondary chains. For 15 years
the crater chains remained unexplained.  In light of P/SL9's nature,
it is logical to conclude that the crater chains on Callisto (and
Ganymede) were formed when tidally disrupted comets impacted the
Jovian satellites. 

	To date, thirteen crater chains have been identified on
Callisto.  Upon recent re-examination of Voyager's data, three more
similar chains have now been identified on Ganymede.  The next
opportunity to identify and re-examine these features will be when the
Galileo spacecraft enters Jovian orbit in December, 1995. 

				The Planet Jupiter

	Jupiter is the largest of the nine known planets, almost 11
times the diameter of Earth and more than 300 times its mass.  In
fact, the mass of Jupiter is almost 2.5 times that of all the other
planets combined. Being composed largely of the light elements
hydrogen (H) and helium (He), its mean density is only 1.3 times that
of water.  The mean density of Earth is 5.2 times that of water. The
pull of gravity on Jupiter at the top of the clouds at the equator is
2.4 times greater than Earth's surface.  The bulk of Jupiter rotates
once in 9 hours and 56 minutes, although the period determined by
watching cloud features differs by up to five minutes due to intrinsic
cloud motions. 

	The visible "surface" of Jupiter is a deck of clouds of
ammonia crystals, the tops of which occur at a level where the
pressure is about half that at Earth's surface. The bulk of the
atmosphere is made up of 89% molecular hydrogen (H2) and 11% helium
(He). There are small amounts of gaseous ammonia (NH3), methane (CH4),
water (H2O), ethane (C2H6), acetylene (C2H2), carbon monoxide (CO),
hydrogen cyanide (HCN), and even more exotic compounds such as
phosphine (PH3) and germane (GeH4). At levels below the deck of
ammonia clouds there are believed to be ammonium hydro-sulfide (NH4SH)
clouds and water crystal (H2O) clouds, followed by clouds of liquid
water. The visible clouds of Jupiter are very colorful.  The cause of
these colors is not yet known. "Contamination" by various polymers of
sulfur (S3, S4, S5, and S8), which are yellow, red, and brown, has
been suggested as a possible cause of the riot of color, but in fact
sulfur has not yet been detected spectroscopically, and there are many
other candidates as the source of the coloring. 

	The meteorology of Jupiter is very complex and not well
understood. Even in small telescopes, a series of parallel light bands
called zones and darker bands called belts is quite obvious.  The
polar regions of the planet are dark.  Also present are light and dark
ovals, the most famous of these being "the Great Red Spot." The Great
Red Spot is larger than Earth, and although its color has brightened
and faded, the spot has persisted for at least 162.5 years, the
earliest definite drawing of it being Schwabe's of 5 September 1831.
(There is less positive evidence that Hooke observed it as early as
1664.) It is thought that the brighter zones are cloud-covered regions
of upward moving atmosphere, while the belts are the regions of
descending gases, the circulation driven by interior heat. The spots
are thought to be large-scale vortices, much larger and far more
permanent than any terrestrial weather system. 

	The interior of Jupiter is totally unlike that of Earth. Earth
has a solid crust "floating" on a denser mantle that is fluid on top
and solid beneath, underlain by a fluid outer core that extends out to
about half of Earth's radius and a solid inner core of about 1,220-km
radius. The core is probably 75% iron, with the remainder nickel,
perhaps silicon, and many different metals in small amounts. Jupiter
on the other hand may well be fluid throughout, although it could have
a "small" solid core (upwards of 15 Earth masses) of heavier elements
such as iron and silicon extending out to perhaps 15% of its radius.
The bulk of Jupiter is fluid hydrogen in two forms or phases, liquid
molecular hydrogen on top and liquid metallic hydrogen below; the
latter phase exists where the pressure is high enough, say 3-4 million
atmospheres. There could be a small layer of liquid helium below the
hydrogen, separated out gravitationally, and there is clearly some
helium mixed in with the hydrogen.  The hydrogen is convecting heat
(transporting heat by mass motion) from the interior, and that heat is
easily detected by infrared measurements, since Jupiter radiates twice
as much heat as it receives from the Sun.  The heat is generated
largely by gravitational contraction and perhaps by gravitational
separation of helium and other heavier elements from hydrogen, in
other words, by the conversion of gravitational potential energy to
thermal energy.  The moving metallic hydrogen in the interior is
believed to be the source of Jupiter's strong magnetic field. 

	Jupiter's magnetic field is much stronger than that of Earth. 
It is tipped about 11 degrees to Jupiter's rotational axis, similar to
Earth's, but it is also offset from the center of Jupiter by about
10,000 km. The magnetosphere of charged particles which it affects
extends from 3.5 million to 7 million km in the direction toward the
Sun, depending upon solar wind conditions, and at least 10 times that
far in the anti-Sun direction.  The plasma trapped in this rotat- ing,
wobbling magnetosphere emits radio frequency radiation measurable from
Earth at wavelengths from 1 m or less to as much as 30 km. The shorter
waves are more or less continuously emitted, while at longer
wavelengths the radiation is quite sporadic. Scientists will carefully
monitor the Jovian magnetosphere to note the effect of the intrusion
of large amounts of cometary dust into the Jovian magnetosphere. 

	The two Voyager spacecraft discovered that Jupiter has faint
dust rings extending out to about 53,000 km above the atmosphere.  The
brightest ring is the outermost, having only about 800-km width.  Next
inside comes a fainter ring about 5,000 km wide, while very tenuous
dust extends down to the atmosphere. Again, the effects of the
intrusion of the dust from Shoemaker-Levy 9 will be interesting to
see, though not easy to study from the ground. 

			      The Impact into Jupiter

	All 20-plus major impacts will occur at approximately the same
position on Jupiter relative to the center of the planet, but because
the planet is rotating the impacts will occur at different points in
the atmosphere. The impacts will take place at approximately 45
degrees south latitude and 6.5 degrees of longitude from the limb,
just out of view from Earth (approximately 15 degrees from the dawn
terminator). Jupiter has a rotation period of 9.84 hours, or a
rotation rate of about 0.01 degrees/sec, so the impacts will occur on
the farside of the planet but the point of impact in the atmosphere
will rotate across the limb within about 11 minutes after the impact,
and cross the dawn termninator within about 25 minutes from the
impact. >From this point on the effects on the atmosphere should be
observable from Earth, but the viewing of the atmosphere where the
impact occurred will improve as the site rotates towards the center of
the disk and we can see it face on.  The comet particles will be
moving almost exactly from (Jovian) south to north at the time of the
impact, so they will strike the planet at an angle of 45 degrees to
the surface. (The surface is defined for convenience as the Jovian
cloud tops.) The impact velocity will be Jovian escape velocity, 60
km/sec. 

	The times of collision of these fragments with Jupiter can
only be currently estimated within about 20 minutes. As measurements
of the orbit are made over the next few months the accuracy of these
estimates should improve, so by June 1 the impact time will be known
with an accuracy of about 16 minutes and by July 1 about 10 minutes.
Eighteen hours before the first impact the uncertainty will be
approximately 3 minutes. The relative positions of the fragments to
each other are known much more accurately than the absolute position,
so once the first fragment impacts Jupiter, the collision times of the
remaining fragments will be better constrained.  The first fragment,
A, will collide with Jupiter on 16 July at 19:13 Universal Time (UT). 
Jupiter will be approximately 5.7 AU (860 million km) from Earth, so
the time for light to travel to the Earth will be about 48 minutes,
and the collision will be observed on Earth at 20:01 UT (16:01 PM EDT)
on 16 July. 

	For Earth-based observations, Jupiter will rise at about noon
and set around midnight, so there will be a limited window to observe
the collisions.  The head of the dust train around the fragments will
reach Jupiter 1 to 2 months before the particles arrive. 

	The predicted outcomes of the impacts with Jupiter span a
large range. This is due in part to the uncertainty in the size of the
impacting bodies but even for a fixed size there is a wide range of
predictions, largely because planetary scientists have never observed
a collision of this magnitude.  It is not known what the effects of
the impacts of the large fragments will be on Jupiter, the large mass
(~1012 to 1014 kg) and high velocity (60 km/sec) guarantee highly
energetic collisions.  Various models of this collision have been
hypothesized, and there is general agreement that a fragment will
travel through the atmosphere to some depth and explode, creating a
fireball which will rise back above the cloud tops. The explosion will
also produce pressure waves in the atmosphere and "surface waves" at
the cloud tops.  The rising material may consist of an equal amount of
vaporized comet and Jovian atmosphere, but details about this, the
depth of the explosion, the total amount of material ejected above the
cloud tops, and almost all other effects of the impact are highly
model dependent. Each impact (and the subsequent fall-back of ejected
material over a period of ~3 hours after the collision will probably
affect an area of the atmosphere from one to a few thousand km around
the impact site. It will be difficult to see the objects within about
8 Jovian radii (~570,000 km). 

	If the cometary nuclei have the sizes estimated from the
observations with the Hubble Space Telescope and if they have the
density of ice, each fragment will have a kinetic energy equivalent to
roughly 10 million megatons of TNT (10^29 to 10^30 ergs).  The total
energy of the collisions [of all fragments] may be as great as 100
million megatons of TNT; roughly 10,000 times the total destructive
power of the world's nuclear arsen at the height of the Cold War.  The
impacts will be as energetic as the collision of a large asteroid or
comet with the Earth 65 million years ago.  This latter cosmic
catastrophe most probably led to the extinction of the dinosaurs and
hundreds of other species at the geologic Cretaceous-Tertiary (K-T)
boundary layer. 

	The predictions of the effects differ in how they model the
physical pro- cesses and there are significant uncertainties about
which processes will dominate the interaction.  If ablation (melting
and vaporization) and fragmentation dominate, the energy can be
dissipated high in the atmosphere with very little material
penetrating far beneath the visible clouds.  If the shock wave in
front of the fragment also confines the sides and causes the fragment
to behave like a fluid, then nuclei could penetrate far below the
visible clouds.  Even in this case, there are disagreements about the
depth to which the material will penetrate, with the largest estimates
being several hundred kilometers below the cloudtops. 

	The short-term effects at the atmospheric site of impact may
be profound. Thermal plumes may rise to 700 km.  Whether permanent
disturbances, such as a new Great Red Spot or White Ovals form, is
also a subject of great debate.  The HST will monitor the atmosphere
for changes in cloud morphology as each impact site rotates into view
within a couple hours of the impact. 

	In any case, there will be an optical flash lasting a few
seconds as each nucleus passes through the stratosphere.  The
brightness of this flash will depend critically on the fraction of the
energy which is released at these altitudes.  If a large fragment
penetrates below the cloudtops and releases much of its energy at
large depths, then the initial optical flash will be faint but a
buoyant hot plume will rise in the atmosphere like the fireball after
a nuclear explosion, producing a second, longer flash lasting a minute
or more and radiating most strongly in the infrared.  Although the
impacts will occur on the far side of Jupiter, estimates show that the
flashes may be bright enough to be observed from Earth in reflection
off the inner satellites of Jupiter, particularly Io, if a satellite
happens to be on the far side of Jupiter but still visible as seen
from Earth.  The flashes will also be directly visible from the
Galileo spacecraft. 

	The shock waves produced by the impact onto Jupiter are
predicted to penetrate into the interior of Jupiter, where they will
be bent, much as the seismic waves from earthquakes are bent in
passing through the interior of Earth. These may lead to a prompt
(within an hour or so) enhancement of the thermal emission over a very
large circle centered on the impact.  Waves reflected from the
density-discontinuities in the interior of Jupiter might also be
visible on the front side within an hour or two of the impact. 
Finally, the shock waves may initiate natural oscillations of Jupiter,
similar to the ringing of a bell, although the predictions disagree on
whether these oscillations will be strong enough to observe with the
instrumentation currently available.  Observation of any of these
phenomena can provide a unique probe of the interior structure of
Jupiter, for which we now have only theoretical models with almost no
observational data. 

	The plume of material that would be brought up from Jupiter's
troposphere (below the clouds) will bring up much material from the
comet as well as material from the atmosphere itself.  Much of the
material will be dissociated and even ionized but the composition of
this material can give us clues to the chemical composition of the
atmosphere below the clouds.  It is also widely thought that as the
material recombines, some species, notably water, will condense and
form clouds in the stratosphere.  The spreading of these clouds in
latitude and longitude can tell us about the circulation in the
stratosphere and the altitude at which the clouds form can tell us
about the composition of the material brought up from below.  The
grains of the comet which impact Jupiter over a period of several
months may form a thin haze which will also circulate through the
atmosphere.  Enough clouds might form high in the stratosphere to
obscure the clouds at lower altitudes that are normally seen from Earth. 

	Interactions of cometary material with Jupiter's magnetic
field have been predicted to lead to observable effects on Jupiter's
radio emission, in- jection of material into Jupiter's auroral zone,
and disruption of the ring of grains that now encircles Jupiter. 

	Somewhat less certainly the material may cause observable changes in 
the torus of plasma that circles Jupiter in association with the orbit of Io 
or may release gas in the outer magnetosphere of Jupiter.  It has also been 
predicted that the cometary material may, after ten years, form a new ring 
about Jupiter although there are some doubts whether this will happen.

		    ###next:  Overview of HST####

------------------------------

Topic No. 3

Date: Tue, 24 May 1994 15:47:59 -0400 (EDT)
From: Robert Landis <[email protected]>
To: "Planetarian's Digest" <[email protected]>
Subject: P/SL9-Jupiter fr. yr. Pltm - Part 3 of 4
Message-ID: <[email protected]>

		     Overview of the Hubble Space Telescope

	The Hubble Space Telescope is a coooperative program of the European 
Space Agency (ESA) and the National Aeronautics and Space Administration (NASA)
to operate a long-lived space-based observatory for the benefit of the inter-
national astronomical community.  HST is an observatory first dreamt of in
the 1940s, designed and built in the 1970s and 80s, and operational only in the
1990s.  Since its preliminary inception, HST was designed to be a different type
of mission for NASA -- a permanent space-based observatory.  To accomplish this
goal and protect the spacecraft against instrument and equipment failures, NASA
had always planned on regular servicing missions.  Hubble has special grapple
fixtures, 76 handholds, and stabilized in all three axes.

	When originally planned in 1979, the Large Space Telescope
program called for return to Earth, refurbishment, and relaunch every
5 years, with on-orbit servicing every 2.5 years.  Hardware lifetime
and reliability requirements were based on that 2.5-year interval
between servicing missions.  In 1985, contamina- tion and structural
loading concerns associated with return to Earth aboard the shuttle
eliminated the concept of ground return from the program.  NASA
decided that on-orbit servicing might be adequate to maintain HST for
its 15-year design life.  A three year cycle of on-orbit servicing was
adopted.  The first HST servicing mission in December 1993 was an
enormous success.  Future servicing missions are tentatively planned
for March 1997, mid-1999, and mid-2002.  Contingency flights could
still be added to the shuttle manifest to perform specific tasks that
cannot wait for the next regularly scheduled servicing mission (and/or
required tasks that  were not completed on a given servicing mission).

	The four years since the launch of HST in 1990 have been
momentous, with the discovery of spherical aberration and the search
for a practical solution. The STS-61 (Endeavour) mission of December
1993 fully obviated the effects of spherical aberration and fully
restored the functionality of HST. 

			The Science Instruments

Wide Field/Planetary Camera 2

	The original Wide Field/Planetary Camera (WF/PC1) was changed
out and displaced by WF/PC2 on the STS-61 shuttle mission in December
1993.  WF/PC2 was a spare instrument developed in 1985 by the Jet
Propulsion Laboratory in Pasadena, California. 

	WF/PC2 is actually four cameras.  The relay mirrors in WF/PC2 are 
spherically aberrated to correct for the spherically aberrated primary mirror 
of the observatory.  (HST's primary mirror is 2 microns too flat at the edge, 
so the corrective optics within WF/PC2 are too high by that same amount.)

	The "heart" of WF/PC2 consists of an L-shaped trio of
wide-field sensors and a smaller, high resolution ("planetary") camera
tucked in the square's remaining corner. 

	WF/PC2 has been used to image P/SL9 and will be used
extensively to "map" Jupiter's features before, during, and after the
collision events. 

Corrective Optics Space Telescope Axial Replacement 

	COSTAR is not a science instrument; it is a corrective optics
package that displaced the High Speed Photometer during the first
servicing mission to HST. COSTAR is designed to optically correct the
effects of the primary mirror's aberration on the three remaining
scientific instruments:  Faint Object Camera (FOC), Faint Object
Spectrograph (FOS), and the Goddard High Resolution Spectrograph (GHRS). 

Faint Object Camera

	The Faint Object Camera is built by the European Space Agency.
 It is the only instrument to utilize the full spatial resolving power
of HST. 

	There are two complete detector system of the FOC.  Each uses
an image intensifier tube to produce an image on a phosphor screen
that is 100,000 times brighter than the light received.  This phosphor
image is then scanned by a sensitive electron-bombarded silicon (EBS)
television camera.  This system is so sensitive that objects brighter
than 21st magnitude must be dimmed by the camera's filter systems to
avoid saturating the detectors.  Even with a broad-band filter, the
brightest object which can be accurately measured is 20th magnitude. 

	The FOC offers three different focal ratios: f/48, f/96, and
f/288 on a standard television picture format.  The f/48 image
measures 22 X 22 arc-seconds and yields resolution (pixel size) of
0.043 arc-seconds.  The f/96 mode provides an image of 11 X 11
arc-seconds on each side and a resolution of 0.022 arc-seconds. The
f/288 field of view is 3.6 X 3.6 arc-seconds square, with resolution
down to 0.0072 arc-seconds. 

Faint Object Spectrograph

	A spectrograph spreads out the light gathered by a telescope
so that it can be analyzed to determine such properties of celestial
objects as chemical composition and abundances, temperature, radial
velocity, rotational velocity, and magnetic fields. The Faint Object
Spectrograph (FOS) exmaines fainter objects than the HRS, and can
study these objects across a much wider spectral range from the UV
(1150 A) through the visible red and the near-IR (8000 A). 

	The FOS uses two 512-element Digicon sensors (light
intensifiers) to light. The "blue" tube is sensitive from 1150 to 5500
A (UV to yellow).  The "red" tube is sensitive from 1800 to 8000 A
(longer UV through red).  Light can enter the FOS through any of 11
different apertures from 0.1 to about 1.0 arc-seconds in diameter. 
There are also two occulting devices to block out light from the
center of an object while allowing the light from just outside the
center to pass on through. This could allow analysis of the shells of
gas around red giant stars of the faint galaxies around a quasar. 

	The FOS has two modes of operation PP low resolution and high
resolu- tion.  At low resolution, it can reach 26th magnitude in one
hour with a resolving power of 250.  At high resolution, the FOS can
reach only 22nd magnitude in an hour (before S/N becomes a problem),
but the resolving power is increased to 1300. 

Goddard High Resolution Spectrograph

	The High Resolution Spectrograph also separates incoming light
into its spectral components so that the composition, temperature,
motion, and other chemical and physical properties of the objects can
be analyzed.  The HRS contrasts with the FOS in that it concentrates
entirely on UV spectroscopy and trades the extremely faint objects for
the ability to analyze very fine spectral detail.  Like the FOS, the
HRS uses two 521-channel Digicon electronic light detectors, but the
detectors of the HRS are deliberately blind to visible light. One tube
is sensitive from 1050 to 1700 A; while the other is sensitive from
1150 to 3200 A. 

	The HRS also has three resolution modes:  low, medium, and
high.  "Low resolution" for the HRS is 2000 A higher than the best
resolution available on the FOS.  Examining a feature at 1200 A, the
HRS can resolve detail of 0.6 A and can examine objects down to 19th
magnitude.  At medium resolution of 20,000; that same spectral feature
at 1200 A can be seen in detail down to 0.06 A, but the object must be
brighter than 16th magnitude to be studied.  High resolution for the
HRS is 100,000; allowing a spectral line at 1200 A to be resolved down
to 0.012 A.  However, "high resolution" can be applied only to objects
of 14th magnitude or brighter.  The HRS can also discriminate between
variation in light from ojbects as rapid as 100 milliseconds apart. 

			Mission Operations and Observations

	Although HST operates around the clock, not all of its time is
spent observing.  Each orbit lasts about 95 minutes, with time
allocated for housekeeping functions and for observations. 
"Housekeeping" functions includes turning the telescope to acquire a
new target, or avoid the Sun or Moon, switching communica- tions
antennas and data transmission modes, receiving command loads and
downlinking data, calibrating and similar activities. 

	When STScI completes its master observing plan, the schedule
is forwarded to Goddard's Space Telescope Operations Control Center
(STOCC), where the science and housekeeping plans are merged into a
detailed operations schedule.  Each event is translated into a series
of commands to be sent to the onboard computers.  Computer loads are
uplinked several times a day to keep the telescope operating
efficiently. 

	When possible two scientific instruments are used
simultaneously to observe adjacent target regions of the sky.  For
example, while a spectrograph is focused on a chosen star or nebula,
the WF/PC can image a sky region offset slightly from the main viewing
target.  During observations the Fine Guidance Sensors (FGS) track
their respective guide stars to keep the telescope pointed steadily at
the right target. 

	In an astronomer desires to be present during the observation,
there is a console at STScI and another at the STOCC, where monitors
display images or other data as the observations occurs.  Some limited
real-time commanding for target acquisition or filter changing is
performed at these stations, if the observation program has been set
up to allow for it, but spontaneous control is not possible. 

	Engineering and scientific data from HST, as well as uplinked
operational commands, are transmitted through the Tracking Data Relay
Satellite (TDRS) system and its companion ground station at White
Sands, New Mexico.  Up to 24 hours of commands can be stored in the
onboard computers.  Data can be broadcast from HST to the ground
stations immediately or stored on tape and downlinked later. 

	The observer on the ground can examine the "raw" images and
other data within a few minutes for a quick-look analysis.  Within 24
hours, GSFC formats the data for delivery to the STScI.  STScI is
responsible for data processing (calibration, editing, distribution,
and maintenance of the data for the scientific community). 

	Competition is keen for HST observing time.  Only one of every
ten proposals is accepted.  This unique space-based observatory is
operated as an international research center; as a resource for
astronomers world-wide. 

	The Hubble Space Telescope is the unique instrument of choice
for the upcom- ing collision of Comet Shoemaker-Levy 9 into Jupiter. 
The data gleaned from this momentous event will be invaluable for
decades to come. 

				Other Spacecraft

Galileo

	Galileo is enroute to Jupiter and will be about 1.5 AU (230
million km) from Jupiter at the time of the impact.  At this range,
Jupiter will be ~60 pixels across in the solid state imaging camera, a
resolution of ~2400 km/pixel. Galileo will have a direct view of the
impact sites, with an elevation of approx- imately 23 degrees above
the horizon as seen from the impact point.  The unavaila- bility of
the main antenna, forcing use of the low-gain antenna for data trans-
mission, severely limits the imaging options available to Galileo. The
low-gain antenna will be able to transmit to Earth at 10 bits/sec, so
real-time transmission of imaging will not be possible.  The Galileo
tape recorder can store ~125 full-frame equivalents. On-board data
compression and mosaicking may allow up to 64 images per frame to be
stored, but playback of the recorded images must be completed by
January, 1995 when Galileo reaches Jupiter.  This will only allow
transmission of ~5 full-frame equivalents, or approximately 320
images.  There will be the capability for limited on-board editing and
the images can be chosen after the impacts have occured, so the impact
timing will be well known, but the imaging times must be scheduled
weeks before the impacts. Each image requires 2.33 seconds, so a full
frame of 64 images will cover ~2.5 minutes, and consist of ~2400
kilobits. A new mosaic can be started in ~6 seconds.  The camera has a
number of filters from violet through near-IR and requires 5 to 10
seconds to change filters. In addition to imaging data, Galileo has a
high time resolution photopolarimeter radiometer, near-infrared
mapping spectrometer, radio reciever, and ultraviolet spectrometer
which can be used to study the collisions. The limited storage
capacity and low transmission rate of Galileo make the timing of all
the impact observations critical. 

Ulysses

	The Ulysses spacecraft is in a high inclination orbit relative
to the ecliptic plane, which will carry it under the south pole of the
Sun in September 1994.  Its payload includes sensitive radio receivers
that may be able to observe both the immediate consequences of the
collisions of Comet Shoemaker-Levy 9 frag- ments with Jupiter and the
long-term effects on the Jovian magnetosphere. 

	Ulysses will be 2.5 AU (375 million km) south of Jupiter at
the time of impact and will also have a direct line of sight to the
impact point. From this position the Ulysses unified radio and plasma
wave (URAP) experiment will monitor radio emissions between 1 and 940
KHz, sweeping through the spectrum approximately every 2 minutes. URAP
will be able to detect radio emissions down to 1014 ergs.  There are
no imaging experiments on Ulysses. 

Voyager 2

	Voyager 2 is on it's way out of the solar system, 44 AU from
Jupiter at the time of the impact. The planetary radio astronomy (PRA)
experiment will be monitoring radio emissions in the 1 KHz to 390 KHz
range with a detection limit of 1019 to 1020 ergs.  PRA will sweep
through this spectrum every 96 seconds. The Voyager 2 imaging system
will not be used. 

International Ultraviolet Explorer

	The International Ultraviolet Explorer (IUE) satellite will be
devoting 55 eight-hour shifts (approximately 2-1/2 weeks total) of
ultraviolet (UV) spectroscopic observations to the Comet
Shoemaker-Levy 9 impact events, with 30 shifts allotted to the
American effort (Principal Investigators:  Walt Harris, University of
Michigan; Tim Livengood, Goddard Space Flight Center; Melissa McGrath,
Space Telescope Science Institute) and 25 shifts allotted to the
European effort (PIs: Rene Prange, Institute d'Astrophysique Spatiale;
Michel Festou, Observatoire Midi-Pyrenees).  The observing campaign
will begin with baseline observations in mid-June, and continue
through mid-August.  During the week of the actual impacts,  IUE will
be observing the Jovian system continuously. 

	The IUE campaign will be devoted to in-depth studies of the
Jovian aurorae, the Jovian Lyman-alpha bulge, the chemical composition
and structure of the upper atmosphere, and the Io torus.  The IUE
observations will provide a comprehensive study of the physics of the
cometary impact into the Jovian atmosphere, which can provide new
insights into Jupiter's atmospheric structure, composition, and
chemistry, constrain global diffusion processes and timescales in the
upper atmosphere, characterize the response of the Lyman-alpha bulge
to the impacting fragments and associated dust, study the atmospheric
modification of the aurora by the impact material deposited by the
comet and by the material ejected into the magnetosphere from the deep
atmosphere, and investigate the mass loading processes in the magnetosphere. 

Ground-Based

	Many large telescopes will be available on Earth with which to
observe the phenomena associated with the Shoemaker-Levy 9 impacts on
Jupiter in visible, infrared, and radio wavelengths.  Small portable
telescopes can fill in gaps in existing observatory locations for some
purposes. Imaging, photometry, spectroscopy, and radiometry will
certainly be carried out using a multitude of detectors. Many of these
attempts will fail, but some should succeed.  Apart from the obvious
difficulty that the impacts will occur on the back side of Jupiter as
seen from Earth, the biggest problem is that Jupiter in July can only
be observed usefully for about two hours per night from any given
site.  Earlier the sky is still too bright and later the planet is too
close to the horizon. Therefore, to keep Jupiter under continuous
surveillance would require a dozen observatories equally spaced in
longitude clear around the globe. A dozen observatories is feasible,
but equal spacing is not. There will be gaps in the coverage, notably
in the Pacific Ocean, where Mauna Kea, Hawaii, is the only
astronomical bastion. 

				The Kuiper Airborne Observatory (KAO)

	The KAO is a modified C-141 aircraft with a 36-inch (0.9
meter) telescope mounted in it.  The telescope looks out the left side
of the airplane through an open hole in the fuselage.  No window is
used because a window would increase the infrared background level. 
The telescope is stabilized by: 1) a vibration isolation system (shock
absorbers); 2) a spherical air bearing; 3) a gyroscope controlled
pointing system; and 4) an optical tracking system.  The telescope can
point to a couple of arc-seconds even in moderate turbulence. 

	The airplane typically flies at 41,000 feet (12.5 km), above
the Earth's tropopause.  The temperature is very cold there, about -50
degrees Celsius, so water vapor is largely frozen out.  There is about
10 precipitable microns of water in the atmospheric column above the
KAO (about the same amount as in the atmosphere of Mars).  This allows
the KAO to observe most of the infrared wavelengths that are obscured
by atmospheric absorption at ground-based sites. Flights are normally
7.5 hours long, but the aircraft has flown observing missions as long
as 10 hours.  The comet impact flights are all around 9.5 hours to
maximize the observing time on Jupiter after each impact.  Because
these observations will be made in the infrared and the infrared sky
is about as dark in the daytime as it is at night, we will be able to
observe in the afternoon and into the evening. 

	The main advantage that the airborne observatory brings to
bear is its ability to observe water with minimal contamination by
terrestrial water vapor. The observing projects focus on observing
tropospheric water (within Jupiter's cloud deck) brought up by the
comet impact, or possibly on water in the comet if it breaks up above
Jupiter's tropopause.  The KAO team will also look for other compounds
that would be unobservable from the ground due to terrestrial
atmospheric absorption. 

	The KAO will be deployed to Australia to maximize the number
of times the immediate aftermath of an impact can be observed.  The
available integration time on each flight will be typically 4-5 hours,
from impact time to substantially after the central meridian crossing
of the impact point.  The KAO will leave NASA Ames on 12 July, return
on 6 August.  The last part of the deployment will be devoted to
observations of southern hemisphere objects as part of the regular
airborne astronomy program. 

		###next:  HST Science Observation Teams###

------------------------------

Topic No. 4

Date: Tue, 24 May 1994 15:48:26 -0400 (EDT)
From: Robert Landis <[email protected]>
To: "Planetarian's Digest" <[email protected]>
Subject: P/SL9-Jupiter fr. yr. Pltm - Part 4 of 4
Message-ID: <[email protected]>

			HST Science Observation Teams

Spectroscopy

	The Jupiter spectroscopy team headed by Keith Noll (STScI)
will search for molecular remnants of the comet and fireball in
Jupiter's upper atmosphere.  The team consists of seven investigators:
 Noll (STScI), Melissa McGrath (STScI), L. Trafton (University of
Texas),  Hal Weaver (STScI),  J. Caldwell (York University), Roger
Yelle (University of Arizona),  and S. Atreya (University of Michigan). 

		Even though the comet's mass is dwarfed by the mass of
Jupiter, the impact can cause local disturbances to the composition of
the atmosphere that could be detectable with HST.  The two
spectrometers on HST, the Faint Object Spectrograph (FOS) and the
Goddard High Resolution Spectrograph (HRS), will be used to search for
the spectral fingerprints of unusual molecules near the site of one of
the large impacts. 

	Jupiter's stratosphere will be subject to two sources of
foreign material, the comet itself, and gas from deep below Jupiter's
cloudtops.  There are large uncertainties in the predictions of how
deep the comet fragments will penetrate into Jupiter's atmosphere
before they are disrupted.  But, if they do penetrate below Jupiter's
clouds as predicted by some, a large volume of heated gas could rise
into Jupiter's stratosphere.  As on the Earth, Jupiter's stratosphere
is lacking in the gases that condense out at lower altitudes.  The
sudden introduction of gas contain- ing some of these condensible
molecules can be likened to what happens on Earth when a volcano such
as Pinatubo injects large amounts of gas and dust into the
stratosphere. Once in this stable portion of the atmosphere on either
planet, the unusual material can linger for years. 

	The spectroscopic investigation will consist of 12 orbits
spread over three complementary programs.  Several of the observations
will be done within the first few days after the impact of fragment G
on 18 July at 07:35 UTC.  The team also wants to study how the atmosphere 
evolves so some observations will continue into late August. 

	The FOS will obtain broad-coverage spectra from ~1750 - 3300
A. Quite a few atmospheric molecules have absorptions in this
interval, particularly below 2000 A. One molecule that we will look
for with special interest is hydrogen sulfide (H2S), a possible ingredient 
for the still-unidentified coloring agent in Jupiter's clouds. 

	The spectroscopy team will focus in on two spectral intervals
with the HRS. In one experiment, the team will search for silicon
oxide (SiO) which should be produced from the rocky material in the
cometary nucleus.  The usefulness of this molecule is the fact that it
can come only from the comet since any silicon in Jupiter's atmosphere
resides far below the deepest possible penetration of the frag- ments.
Measuring this will help sort out the relative contributions of the
comet and Jupiter's deep atmosphere to the disturbed region of the
stratosphere.  Finally, the spectroscopy team will use the HRS to
search for carbon monoxide (CO) and other possible emissions near 1500
A.  CO is an indicator of the amount of oxygen introduced into the
normally oxygen-free stratosphere.  Any results obtained with the HRS
will be combined with ground-based observations of CO at infrared
wavelengths sensitive to deeper layers to reconstruct the variation of
CO with altitude. 

Atmospheric Dynamics

	The HST Jupiter atmospheric dynamics team, led by Heidi Hammel
(Massachu- setts Institute of Technology), will be carefully
monitoring Jupiter to observe how its atmosphere reacts to incoming
cometary nuclei.  The atmospheric dynamics team consists of four
investigators:  Hammel (MIT),  Reta Beebe (New Mexico State
University), Andrew Ingersoll (California Institute of Technology),
and Glenn Orton (JPL/Caltech). 

	Researchers at the Massachusetts Institute of Technology have
conducted computer simulations of the collisions' effect on Jupiter's
weather.  These simulations show waves travelling outward from the
impact sites and propagating around the planet in the days following
each impact.  The predicted "inertia- gravity" waves are on Jupiter's
"surface" (atmosphere) may emanate from the impact sites and would be
analagous to the ripples from dropping a pebble in a pond. 

	Some theorists believe that the waves will be "seismic" in
nature, with the atmosphere of Jupiter ringing like a bell.  Such
phenomenon may occur within the first hours after an impact.  These
seismic waves would travel much faster than the inertia-gravity waves,
and quite likely more difficult to detect. 

	Using HST, Hammel's team hopes to detect and observe the
inertia-gravity waves which may take hours to days.  The temperature
deviation in such a typical wave may be as much as 0.1 to 1! Celsius;
quite possibly visible from Earth in the best telescopic views. 

	The speed at which these waves travel depends on their depth
in the atmos- phere and on stability parameters that are only poorly
known.  While Hammel's team will observe the impact and its aftermath
with the Hubble Space Telescope, researchers Joseph Harrington and
Timothy Dowling, also of MIT, will utilize the NASA Infrared Telescope
Facility on Mauna Kea, Hawaii.  Both groups hope to measure wave
speeds and thus determine the Jovian atmospheric parameters more
accurately.  Better-known parameters will, in turn, improve
understanding of planetary weather systems. 

	Another exciting possibility is that new cloud features may
form at the impact locations.  These clouds might then be trapped by
surrounding high-speed jets and spun up into vortices that might last
for days or weeks. 

	Finally,  cometary material will impact Jupiter's upper
atmosphere. This material (ices and dust) could significantly alter
the reflectivity of the atmosphere, and could linger for weeks or 
months.   The goal of Hammel's HST observing plan is to observe all of
these phenomena, while simultaneously and comprehensively mapping of
Jupiter's atmosphere. 

	The primary "products" will be multicolor WF/PC "maps"
(images) of Jupiter. These new WF/PC2 maps will be compared against
the latest Jupiter images with older, WF/PC1 images, as well as
Voyager spacecraft images of Jupiter.  At the very least,  an
exquisite time-lapse series of the best images of Jupiter ever
acquired by ground-based astronomy and spacecraft will be obtained. 

								ATTACHMENT A

Current [as of 16 May 1994] HST Observing and Collision Event Timeline for
P/Shoemaker-Levy and Jupiter 

29 Apr 94:   Updated A. Storrs/R. Landis.  

	     Revised by R. Landis to account for new impact times
	     based on JPL data from D. Yeomans/P. Chodas.

___________________________________________________________________
	   
Orb# Starting Time:   SAA               Activity:
			(start--end)


    195                                 FOC-- Prangee 
    195                                 FOC-- Prangee 
    195                                 FOS-- Noll
    195                                 HRS-- Noll (SiO) 
*   195:23:40:00                       
*   196:00:23:57                       
*   196:02:00:21                       
*   196:03:45:42  4:27--end (05)
*                 4:30--end (02)
*   196:05:22:13  6:10--end (05)
                  6:13--end (02)
*   196:06:58:46  1 min (02)
*   196:08:35:17
*   196:10:11:49
1   196:11:48:21                        WFPC map-- Hammel
2   196:13:24:53                        WFPC map-- Hammel
3   196:15:01:24                 	WFPC map-- Hammel
4   196:16:37:57                 	WFPC map-- Hammel
5   196:18:14:28                 	WFPC map-- Hammel
6   196:19:51:00                 	WFPC map-- Hammel

7   196:21:27:32  21:57--22:17 (05)
8   196:23:04:04  23:33--end   (05)
9   197:00:40:36  01:13--end   (05)
                  01:17--01:30 (02)
10  197:02:17:07  02:53--end   (05)
                  02:57--end   (02)
11  197:03:53:40  04:36--end   (05)
                  04:39--end   (02)
12  197:05:30:11  06:18--end   (05)
                  06:22--end   (02)
13  197:07:06:43
14  197:08:43:15
15  197:10:19:46
16  197:11:56:18                        
17  197:13:32:50                   	    
18  197:15:09:21                   	    
19  197:16:45:53
20  197:18:22:25                                              A impact 197:20:01
21  197:19:58:56  20:35--20:44 (05)     WFPC-- Hammel

22  197:21:35:28  22:02--22:27 (05)
23  197:23:12:00  23:41--end   (05)
                  23:46--23:57 (02)
24  198:00:48:32  01:21--end   (05)
                  01:24--01:38 (02)
25  198:02:25:03  03:02--end   (05)                           B impact 198:03:11
                  03:05--end   (02)
26  198:04:01:35  04:45--end   (05)
                  04:47--end   (02)
27  198:05:38:07  06:27--end   (05)                           
                  06:30--end   (02)                           C impact 198:07:03
28  198:07:14:39                        
29  198:08:51:10                        WFPC-- Clarke
30  198:10:27:42                                              D impact 198:11:58
31  198:12:04:14                            
32  198:13:40:45                        WFPC-- Hammel         E impact 198:14:56
33  198:15:17:17                        WFPC-- Hammel
34  198:16:53:48                        WFPC-- Hammel
35  198:18:30:20                        WFPC-- 1/2 Hammel, 
                                               1/2 Clarke
36  198:20:06:52  20:34--20:53 (05)
37  198:21:43:23  22:09--22:36 (05)
                  22:17--22:22 (02)
38  198:23:19:55  22:48--end   (05)     3 WFPC DARKS
                  23:53--00:05 (02)
39  199:00:56:26                                              
40  199:02:32:58  03:10--end   (05)                           F impact 199:02:37
                  03:13--end   (02)
41  199:04:09:29  04:53--end   (05)
                  04:57--end   (02)
42  199:05:46:01  06:36--end   (05)     FOC--Prangee          
43  199:07:22:33                        WFPC-- Hammel         G impact 199:07:35
44  199:08:59:04                        WFPC-- Hammel
45  199:10:35:35                        FOS-- Noll
46  199:12:12:07
47  199:13:48:39                        WFPC-- Clarke
48  199:15:25:10
49  199:17:01:42
50  199:18:38:12                        HRS-- Noll (SiO)      H impact 199:19:23

51  199:20:14:44  20:39--21:02 (05)
52  199:21:51:16  22:17--22:44 (05)
                  22:22--22:31 (02)
53  199:23:27:47  23:46--end   (05)
                  00:00--00:14 (02)
54  200:01:04:19  01:37--end   (05)
                  01:40--01:57 (02)
55  200:02:40:51                               	     
56  200:04:17:22  05:02--end   (05)    	    	
                  05:05--end   (02)
57  200:05:53:53  06:45--end   (05)     HRS-- Noll (SiO)
                  06:47--end  (02)
58  200:07:30:24                        WFPC-- Hammel
59  200:09:06:56                        WFPC-- Hammel         
60  200:10:43:26                        WFPC-- 1/2 Hammel,    K impact 200:10:40
                                               1/2 Clarke
61  200:12:19:59                        
62  200:13:56:31
63  200:15:33:02                        HRS-- Noll (G140L)
64  200:17:09:34
65  200:18:48:04  19:15--19:27 (05)
66  200:20:22:38  20:45--21:11 (05)
67  200:21:59:08  22:24--22:53 (05)                           L impact 200:21:55
                  22:29--22:39 (02)
68  200:23:35:39  00:03--end   (05)     3 WFPC DARKS
                  00:07--00:23 (02)
69  201:01:12:12  1:45 --end   (05)
                  1:48 --2:05  (02)
70  201:02:48:42  3:28 --end   (05)
                  3:31 --end   (02)
71  201:04:25:14  5:11 --end   (05)         		 			
72  201:06:01:45  6:53 --end   (05)    
73  201:07:38:17
74  201:09:14:47                                              N impact 201:10:25
75  201:10:51:19                       HRS-- Noll (G140L)
76  201:12:27:51                       HRS-- Noll (G140L)
77  201:14:04:22                       WFPC-- Prange (4 ex)                    
78  201:15:40:54                       WFPC-- 1/2 Hammel,    P2 impact 201:15:29
                                              1/2 Clarke
79  201:17:17:26
80  201:18:53:58  19:17--19:37 (05)                          Q2 impact 201:19:27
81  201:20:30:29  20:42--21:19 (05)    WFPC-- Hammel         Q1 impact 201:19:54
                  20:58--21:05 (02)
82  201:22:07:00  22:31--23:02 (05)
                  22:36--23:44 (02)
83  201:23:43:31  00:12--end   (05)
                  00:15--00:32 (02)
84  202:01:20:03  1:53--end    (05)
                  1:57--2:14   (02)
85  202:02:56:35  3:37--end    (05)
                  3:39--end    (02)
86  202:04:33:06  5:19--end    (05)
                  5:22--end    (02)                           R impact 202:05:41
87  202:06:09:38                        WFPC-- Hammel         
88  202:07:46:09                        WFPC-- 1/2 Hammel, 
                                               1/2 Clarke
89  202:09:22:41                        WFPC-- Hammel
90  202:10:59:12                        WFPC-- Hammel
91  202:12:35:43                        WFPC-- 1/2 Hammel,
                                               1/2 Clarke
92  202:14:12:15                        WFPC-- Hammel         S impact 202:15:24
93  202:15:48:46                        FOS-- Noll
94  202:17:25:18                        HRS-- Noll (G140L)    T impact 202:18:30
95  202:19:01:50  19:22--19:45 (05)
96  202:20:38:20  20:59--21:28 (05)
                  21:05--21:14 (02)                           U impact 202:21:43
97  202:22:14:52  22:38--23:09 (05)
                  22:43--22:57
98  202:23:51:23  0:20 --end   (05)     3 WFPC DARKS
                  0:23 --0:39  (02)
99  203:01:27:55  2:02 --end   (05)
                  2:05 --end   (02)
100 203:03:04:27  3:16 --end   (05)
                  3:18 --end   (02)                           
101 203:04:40:57  5:28 --end   (05)                           V impact 203:04:48
                  5:31 --end   (02)
102 203:06:17:29                        WFPC-- Hammel
103 203:07:54:01                        WFPC-- Hammel         W impact 203:08:19
104 203:09:30:32                        WFPC-- 1/2 Hammel, 
                                               1/2 Clarke
105 203:11:07:04                        
106 203:12:43:35                        HRS-- Noll (SiO, 3x8)
107 203:14:20:07                        HRS-- Noll (SiO,2x12)
108 203:15:56:38
109 203:17:33:10  17:55--18:10 (05)
110 203:19:09:41  19:28--19:54 (05)
			 1 min (02) 
111 203:20:46:12  21:07--21:36 (05)
                  21:12--21:23 (02)
112 203:22:22:44  22:46--23:17 (05)
                  22:50--23:06 (02)
113 203:23:59:16  0:28 --end   (05)
                  0:32 --0:48  (02)
114 204:01:35:47  2:12 --end   (05)
                  2:14 --end   (02)
115 204:03:12:19  3:54 --end   (05)
                  3:57 --end   (02)
116 204:04:48:50  5:37 --end   (05)
                  5:39 --end   (02)
117 204:06:25:21                         WFPC map-- Hammel
118 204:08:01:53                         WFPC map-- Hammel
119 204:09:38:25                         WFPC map-- Hammel
120 204:11:14:57 	                 WFPC map-- Hammel
121 204:12:51:27  	                 WFPC map-- Hammel
122 204:14:27:59  	                 WFPC map-- Hammel
123 204:16:04:31
124 204:17:41:02  17:58--18:20 (05)
125 204:19:17:34  19:35--20:02 (05)
                  19:42--19:48 (02)
126 204:20:54:08  21:14--21:44 (05)
                  21:18--21:32 (02)
127 204:22:30:58  22:50--23:24 (05)
                  22:58--23:14 (02)
128 205:00:07:09  0:37 --end   (05)
                  0:40 --end   (02)
129 205:01:43:41  2:20 --end   (05)
                  2:23 --end   (02)
130 205:03:20:13  4:03 --end   (05)
                  4:05 --end   (02)
131 205:04:56:44  5:45 --end   (05)
                  5:49 --end   (02)
132 205:06:53:16                        HRS-- McGrath
133 205:08:09:47                        HRS-- McGrath
134 205:09:46:19                        HRS-- McGrath
135 205:11:22:51                        HRS-- McGrath
136 205:12:59:22                        HRS-- McGrath
137 205:14:35:54                        HRS-- McGrath
138 205:16:12:26  16:38--16:44 (05)
139 205:17:48:57  18:04--18:28 (05)
140 205:19:25:29  19:42--20:11 (05)
                  19:48--19:57 (02)
141 205:21:02:00  21:22--21:52 (05)
                  21:25--21:40 (02)
142 205:22:38:32  23:03--23:32 (05)
                  23:07--23:23 (02)
143 206:00:15:04  0:46 --end   (05)
                  0:48 --end   (02)
144 206:01:51:36  2:28 --end   (05)
                  2:32 --end   (02)
145 206:03:28:07  4:12 --end   (05)
                  4:14 --end   (02)
146 206:05:04:39  5:54 --end   (05)
147 206:06:41:11                        FOS-- McGrath
148 206:08:17:42                        FOS-- McGrath
149 206:09:54:15                        FOS-- McGrath
150 206:11:30:46                        FOS-- McGrath
151 206:13:07:17                        FOS-- McGrath (Shemansky)
152 206:14:43:49                        FOS-- McGrath (Shemansky)
    206:16:20:21  16:35--16:54 (05)
    206:17:56:53  18:11--18:37 (05)
                  18:18--18:23 (02)
    206:19:33:24  19:50--20:19 (05)
                  19:54--20:07 (02)
    206:21:09:57  21:29--21:59 (05)
                  21:33--21:49 (02)
    206:22:46:28  23:12--23:39 (05)
                  23:14--23:32 (02)
    206:00:23:00  0:54 --end   (05)
                  0:57 --1:14  (02)
    207:01:59:32  2:37 --end   (05)
                  2:40 --end   (02)
    207:03:36:04  4:20 --end   (05)
                  4:23 --end   (02)
    207:05:12:36  6:03 --end   (05)
    207:06:49:07
    207:08:25:40
    207:10:02:11
    207:11:38:43
    207:13:15:15
    207:14:51:46
    207:16:28:19  16:41--17:03 (05)
    207:18:04:50  18:18--18:45 (05)
                  18:24--18:32 (02)
    207:19:41:23  19:57--20:27 (05)
                  20:01--20:15 (02)
    207:21:17:55  21:38--22:07 (05)
                  21:42--21:57 (02)
    210                                  WFPC-- Clarke
    211      (for 4 orbits)              WFPC map-- Hammel
    222                                  FOC-- Prangee (2 orbits)
    222                                  FOS-- Noll
    222                                  HRS-- Noll (G140L)
    234
    234
    234      (for 5 orbits)              WFPC map-- Hammel
    242 +/- 7d                           FOS-- Noll


Three digit numbers are day of year (1994): day 197 is July 16. All
times are UT (at Earth). Orbit times are from the extrapolation done
on Feb 4, 1994. Impact times are from the 1 Feb. JPL posting. 

All times subject to change due to uncertainty in extrapolation of HST's orbit
and in prediction of impact times.

Note that FGS control cannot be used between 197:06 and 198:13, due to the
proximity of the Moon.

Each orbit (visibility period) lasts 52 min. In the SAA duration
column, ending time labeled "end" means it lasts until the visibility
period of the HST ends. 

The numbers of the orbits here are rather arbitrary. Orbit # 1 here
corresponds to orbit No. 23031 from HST's numbering convention. 

							       ATTACHMENT B

                                                              
			HST, Jupiter, and Comet Bibliography

Popular Books

Kerr, Richard and Elliot, James, Rings:  Discoveries from Galileo to Voyager,
The MIT Press, Cambridge, Massachusetts, 1984.

Littman, Mark, Planets Beyond:  Discovering the Outer Solar System, Wiley
Science Editions, New York, New York, 1988.

Peek, Bertrand M., The Planet Jupiter:  The Observer's Handbook, Faber & Faber
Limited, London, England, 1958 [revised, 1981].

Smith, Robert W., The Space Telescope:  A Study of NASA, Science,
Technology and Politics, Cambridge University Press, Cambridge,
England, 1989 [revised, 1993]. 

Shea, J.F. et al., Report of the Task Force on the Hubble Space Telescope
Servicing Mission (1993).

Magazine Articles

Articles on HST and Comet P/Shoemaker-Levy have appeared in popular magazines
such as Astronomy, Sky & Telescope, Mercury, Discover, Science News, New
Frontier, and The Planetary Report.

Asker, James R., "Spacecraft Armada to Watch Comet Collide with Jupiter,"
Aviation Week & Space Technology, 24 January 1994.

Chaisson, E.J. and Villard, R., "Hubble Space Telescope:  The Mission," Sky &
Telescope, April, 1990.

Fienberg, Richard T., "HST:  Astronomy's Discovery Machine," Sky & Telescope,
April, 1990.

Fienberg, Richard T. "Hubble's Road to Recovery," Sky & Telescope, November
1993.

Hawley, Steven A., "Delivering HST to Orbit," Sky & Telescope, April 1990.

Hoffman, Jeffrey A., "How We'll Fix the Hubble Space Telescope," Sky &
Telescope November 1993. 

Landis, Rob, "Jupiter's Ethereal Rings," Griffith Observer, May 1991.

O'Dell, C.R., "The Large Space Telescope Program," Sky & Telescope, December
1972.

Peterson, Ivars, "Jupiter's Model Spot," Science News, 19 February 1994.

Smith, Douglas L., "When a Body Hits a Body Comin' Through the Sky," Caltech
Alumni Magazine Engineering & Science, Fall 1993.

Tucker, W., "The Space Telescope Science Institute," Sky & Telescope, April
1985.

Villard, Ray, "From Idea to Observation:  The Space Telescope at Work,"
Astronomy, June, 1989.

Villard, Ray, "The World's Biggest Star Catalogue," Sky & Telescope, December
1989.

Scientific Articles

HST science results are published in professional journals such as Geophysical
Research Letters, Icarus, Astronomical Journal, Astrophysical Journal, Nature,
Science, Scientific American, and Space Science Reviews, as well as in the
proceedings of professional organizations.  Some specific articles of interest
include:


Chevalier, Roger A. and Sarazin, Craig L., "Explosions of Infalling Comets in
Jupiter's Atmosphere," submitted to Astrophysical Journal, 20 July 1994.

Kerr, Richard A., "Jupiter Hits May be Palpable Afterall," Science, 262:505, 22
October 1993.

Melosh, H.J. and Schenk, P., "Split Comets and the Origin of Crater Chains on
Ganymede and Callisto," Nature, 365:731-733, 21 October 1993.

Scotti, J.V. and Melosh, H.J., "Estimate of the Size of Comet Shoemaker-Levy 9
from a Tidal Breakup Model, " Nature, 365:733-735, 21 October 1993.

Weaver, H.A. et al., "Hubble Space Telescope Observations of Comet
P/Shoemaker-Levy 9 (1993e)," Science, 263:787-790, 11 February 1994.


								ATTACHMENT C

Abbreviations/Acronym List

COSTAR  Corrective Optics Space Telescope Axial Replacement

ESA  European Space Agency

EVA  Extravehicular Activity

FOC  Faint Object Camera

FOS  Faint Object Spectrograph

FGS  Fine Guidance Sensor

GO  General Observer (also Guest Observer)

GHRS  Goddard High Resolution Spectrograph, also referred to as HRS.

GTO  Guaranteed Time Observer

HST  Hubble Space Telescope

JPL  Jet Propulsion Laboratory

LEO Low-Earth Orbit

MT Moving Targets or Moving Targets Group (at STScI)

NASA  National Aeronautics and Space Administration

NICMOS  Near-Infrared Camera and Multi-Object Spectrometer

OSS  Observation Support Branch (at STScI)

P/SL9  Shorthand for Periodic Comet Shoemaker-Levy 9 (SL9-A refers to
one of the cometary fragments, in this example fragment "A", of the comet) 

RSU  Rate-sensing unit (gyroscope)

SAA  South Atlantic Anomaly

SADE  Solar Array Drive Electronics

SMOV  Servicing Mission Observatory Verification

SPB  Science Planning Branch (at STScI)

SPSS  Science Planning & Scheduling Branch (at STScI)

SOT  Science Observation Team

STIS  Space Telescope Imaging Spectrograph

STS-61  Space Transportation System; the first servicing mission is
the 61st shuttle mission on the manifest since the space shuttle 
first flew in 1981. 

STScI  Space Telescope Science Institute.

WF/PC  (pronounced "wif-pik")  Wide Field/Planetary Camera


							   ATTACHMENT D


A variety of line art supplied by JPL, Lowell Observatory, the University of
Maryland-College Park, and the STScI.  Most is self-explanatory.

Facts at a Glance

One-way light time, Jupiter to Earth:	48 minutes

Radius of Jupiter:			71,350 km (equatorial)
					67,310 km (polar)	
Radius of Earth:			6378 km (equatorial)
					6357 km (polar)
P/Shoemaker-Levy:			4.5? km (equivalent sphere)
P/Halley:				7.65 x 3.60 x 3.61 km
Mass of Jupiter:			1.90 x 1030 g (~318 ME)
Rotation period:			9 hours 56 minutes
Number of known moons:			16
Discovery date P/Shoemaker-Levy:	24 March 1994
Time of first impact (P/SL9-A):		16 July 1994, 20:01 UTC
Time of P/SL9-Q's impact:		20 July 1994, 19:27 UTC
Time of last impact (P/SL9-W):		22 July 1994, 08:09 UTC
HST deployment date:			24 April 1990
HST first servicing mission:		2 - 13 December 1993
Diameter of HST's primary mirror:	2.4 meters
Cost of HST:				$1.5 Billion (1990 dollars)


NASA Select is carried on Spacenet 2, transponder 5, channel 9, 69
degrees West, transponder frequency is 3880 MHz, audio subcarrier is
6.8 MHz, polarization is horizontal. 


Acknowledgements

This document would not be possible if not for the support of the
Science Observation Team and the Science Planning Branch/Moving
Targets Group at the Space Telescope Science Institute.  The selection
of material and any errors are the sole responsibility of the author. 

This paper represents the combined efforts of scientists and science writers 
and is a selected compilation of several texts, original manuscript, and sub-
mitted paragraphs.  Gratitude and many thanks go to Mike A'Hearn (University 
of Maryland), Reta Beebe (New Mexico State University), Ed Bowell (Lowell
Observatory), Paul Chodas (JPL), Ted Dunham (NASA-Ames), Heidi Hammel (MIT), 
Joe Harrington (MIT), Dave Levy, Chris Lewicki (SEDS-University of Arizona),
Mordecai MacLow (University of Chicago), Lucy-Ann McFadden (University of
Maryland), Melissa McGrath (STScI), Ray Newburn (JPL), Keith Noll (STScI),
Elizabeth Roettger (JPL), Jim Scotti (University of Arizona), Dave Seal (JPL),
Carolyn & Gene Shoemaker, Zdenek Sekanina (JPL), Ed Smith (STScI), Lawrence
Wasserman (Lowell Observatory), Hal Weaver (STScI), Don Yeomans (JPL) and to 
all others who may have been omitted.

All comments should be addressed to the author:

Rob Landis
Space Telescope Science Institute
Science Planning Branch/Moving Targets Group
3700 San Martin Drive,
Baltimore, MD  21218

------------------------------

End of DOME-L Digest 164
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From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 26-MAY-1994 
CC:	
Subj:	Comet/Jupiter Collision : New Files

To : SL9 Mailing List

   There are some new PostScript images showing the results of
fireball simulations by Sandia National Laboratories at
tamsun.tamu.edu (128.194.15.32) in the /pub/comet/sandia directory. 
Also, the following files are now available in the /incoming or
/pub/comet directory: 

COMETFAQ.PS   -  Updated PostScript version of comet.faq (May 11, 1994)

TRACKER1.ZIP  -  MSDOS program that displays the location of the Great Red Spot,
                 the white spots FA, BC, and DE during the summer of 1994.
                 Also shown are the impact sites of the comet fragments.

GALSAT52.ZIP  -  Updated MSDOS program that displays the positions of the
                 Galilean Satellites for a given date and time.  The latest
                 impact times and locations are used in the program.  Note
                 that Europa will be in eclipse for impact K.

JUP_P1B.GIF  -  Scanned photo of Jupiter showing two small white ovals south
                of white spots BC and DE of the south temperate belt. The photo
                was taken on May 12, 1994 at 6:40 UT.  Perhaps we should also
                keep an eye one these so that they are not thought to be the
                results of the impacts. (Photo by Don Carona, Texas A&M)

Hope you find these files useful.
Clear skies,
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .

Note : This message was sent via the listserver [email protected].
Replying to this message could send your reply to all subscribers.  Please
send replies to [email protected].  Thanks.

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From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 26-MAY-1994 14:13:18.62
CC:	
Subj:	Hypertext version of SL9 Educator's Guide now available

	I've created a hypertext version of the SL9 Educator's Guide by JPL
for those with WWW access.  To go directly to it, use the URL:

	http://seds.lpl.arizona.edu/sl9/Educator/toc.html

This is also accessible from the SL9 home page:

	http://seds.lpl.arizona.edu/sl9/sl9.html

While some of the figures that accompany the original document aren't 
available, I've created as many substitute links as possible, including
some rather interesting ones (well, I think they're interesting... :-)

JPL has planned for some time to create an "official" hypertext version of
the Educator's Guide.  When this is made available I'll include a link to
it in the SL9 page.  

If you have any comments or suggestions about this version, please e-mail
me at [email protected].

Jeff Foust
[email protected]

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From:	US4RMC::"[email protected]" "MAIL-11 Daemon"  6-JUN-1994 14:09:44.08
CC:	
Subj:	Updated SL9 impact times

[Courtesy of Paul Chodas, JPL]

==============================================================================

Here's a quick update to last week's table of Predicted Impact Parameters.

Our latest orbit solutions use astrometric data two weeks more recent than
those in our last table, and the uncertainties have decreased accordingly.
The predicted impact times have now started to move earlier: about 10 minutes
earlier on average for the major fragments, a half an hour earlier on average
for fragments F, N, and P, and over an hour earlier for A and D.  Fragment U
is the only fragment for which we received no new data; it is still the most
uncertain.

This is a shorter version of the table, which we plan to issue more
frequently.

Paul Chodas
1994 June 5

==============================================================================

Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
- ---------------------------------------------------------------

  P.W. Chodas and D.K. Yeomans (JPL/Caltech)

  Predictions as of 1994 June 3
  Date of last astrometric data in these solutions: 1994 June 1

{This is a shorter version of our earlier table; we plan to issue this
 version more frequently than the full version.}

The predictions for all fragments except Q2 are based on independent orbit
solutions; the orbit reference identifier is given in the rightmost column.
The orbit solution for fragment Q2 was obtained by applying a disruption model
to the orbit for Q1, and using astrometric measurements of Q2 relative to Q1.

Immediately to the right of the predicted impact times, we give the 1-sigma
uncertainties in those times for all fragments except Q2.  We have made an
effort to make these uncertainties realistic: they are not formal uncertainty
values.  NOTE: To obtain a 95% confidence level, one should use a +/- 2 sigma
window around the predicted impact time.  The uncertainties for fragment Q2
have not been quantified, but are probably comparable to those for P2.

The dynamical model used for the predictions includes perturbations due to
the Sun, planets, Galilean satellites and the oblateness of Jupiter.  The
planetary ephemeris used was DE245.

- ----------------------------------------------------------------
Fragment   Impact   1-sig   Jovicentric   Meridian  Angle
          Date/Time  Unc.   Lat.   Long.   Angle    E-J-F   Orbit
         July  (UT) (min)   (deg)  (deg)   (deg)    (deg)    Ref.
- ---------------h--m---------------------------------------------
 A = 21   16  19:55   26   -43.23   176    63.56    99.35    A10
 B = 20   17  03:07   23   -43.45    77    63.67    99.22    B11
 C = 19   17  06:59   24   -43.33   217    64.53    98.64    C8
 D = 18   17  11:18   28   -43.34    14    63.49    99.36    D9
 E = 17   17  15:30   17   -43.70   164    66.13    97.41    E25
 F = 16   18  00:40   23   -43.79   139    64.17    98.77    F16
 G = 15   18  07:52   16   -43.80    37    66.99    96.77    G25
 H = 14   18  19:47   16   -43.86   109    67.32    96.52    H23
 K = 12   19  10:39   16   -43.96   287    68.15    95.90    K24
 L = 11   19  22:40   16   -44.07     2    68.95    95.31    L25
 N = 9    20  10:21   26   -44.59    67    67.13    96.49    N12
 P2= 8b   20  15:27   25   -44.82   253    66.46    96.91    P11
 Q2= 7b   20  19:49        -44.48    48    69.27    95.00
 Q1= 7a   20  20:16   15   -44.20    64    69.69    94.75    Q27
 R = 6    21  05:59   19   -44.27    57    70.24    94.34    R22
 S = 5    21  15:46   17   -44.26    51    70.76    93.97    S32
 T = 4    21  18:16   44   -45.28   145    67.43    96.14    T7
 U = 3    22  00:25   85   -45.19     3    71.74    93.15    U6
 V = 2    22  04:06   31   -44.52   141    68.16    95.77    V8
 W = 1    22  08:34   19   -44.29   299    71.32    93.57    W25

Notes:

1. Fragments J=13 and M=10 are omitted because they have faded from view.
   Fragments P=8 and Q=7 each consist of multiple components.  The March'94
   HST image shows that P1=8a has almost completely faded away (so it too is
   omitted from the Table), and that P2=8b has split.  We do not as yet
   have sufficient data to obtain independent predictions for the two
   components of P2=8b.

2. The impact date/time is the time the impact would be seen at the Earth
   (if the limb of Jupiter were not in the way); the date is the day in
   July 1994; the time is given as hours and minutes of Universal Time.

3. The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

4. The impact longitude is in System III, measured westwards on the planet.

5. The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.  This relative
   longitude is known much more accurately than the absolute longitude.

6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact.  All impacts will be just on the
   farside as viewed from Earth; later impacts are closer to the limb.

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From:	US4RMC::"[email protected]" "MAIL-11 Daemon"  4-JUN-1994 04:56:00.34
CC:	
Subj:	The spectrum of SL9 bolides

To the subscribers of the SL9 list and other members of scientific community.

ON THE SPECTRUM OF THE BOLIDES ARISING DURING THE COLLISION OF
COMET SHOEMAKER-LEVY 9 WITH JUPITER

J. Borovicka, Ondrejov Observatory  ([email protected])

This letter considers the spectrum of the light produced during
the penetration of the fragments of comet SL9 into the atmosphere
of Jupiter. Only simple arguments are used; no detailed calculation
was made. The conclusion is that not only the total brightness of
the bolides but even the shape of the spectrum is highly uncertain.
The observation of spectra of the satellite reflections is of great
scientific importance.
_____________________________________________________________________

In general, we have two possibilities when predicting the radiation
of the bolides of SL9. The first is to extrapolate the experience from
terrestrial meteors, the second is to rely on numerical modelling.

    The summary of terrestrial meteor spectra
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Meteors radiate in individual emission atomic lines and, to less
extent, molecular bands. No continuous thermal radiation has been
observed. See e.g. [1 (page 166), 2, 3] for photographs of meteor
spectra. The spectra can be easily interpreted as the radiation
of a volume of hot gas around the meteoric body. The volume is optically
very thin in continuum but may be optically thick in some lines.

A more detailed analysis [3, 4] revealed the following facts:

1. The ratio of air:meteoric vapors in the hot gas is at least
   10:1 in mass, though the lines of air (N and O) are rather
   faint in the visual region.

2. The cross-section of the radiating volume is at least two orders
   of magnitude larger than the cross-section of the body itself.

3. The spectrum consists in fact of two components. The first component
   is produced by the gas of temperature 4000-5000 K. The main radiators
   are neutral Na, Mg, Fe, Ca, Mn, Cr, and ionized Ca. This component
   dominates in spectra of slow meteors (20 km/s). The second
   component corresponds to the temperature of 10000 K and dominates
   in fast meteors (60 km/s). The main radiators are ionized Ca,
   Mg, Si, and neutral O and H (H alpha line). The difference in
   the radiators is caused by different temperature, not chemical
   composition. The second component is probably connected with the
   shock wave. However, the presence of faint lines of ionized nitrogen
   shows that also higher ionization and excitation than corresponds
   to the temperature of 10000 K occurs in meteors.

    Numerical simulations
    ~~~~~~~~~~~~~~~~~~~~~
were presented in [5]. In the model, the shock wave radiates as
black body with the temperature of 30000 K. This radiation is also
the cause of the ablation of the body. The area of the radiating
shock is the same as the area of the impactor.

    Discussion
    ~~~~~~~~~~
The results of the numerical simulations do not correspond to the
terrestrial experience. Of course, the impact of SL9 on Jupiter
will be a quite different event than the terrestrial meteors. The
main difference is the mass of the impactor, which will be by orders
of magnitude larger. The second difference is the composition
of Jupiter's atmosphere. The intensity of the shock and the opacity
of the negative ion of hydrogen may really enhance the optical thickness
of the shock and it can radiate as blackbody. The open question is
the cross-section of the shock.

However, the lack of thermal radiation in observed meteors raises
some doubts. For example, the Benesov fireball moving at relatively
low height of 25~km above the Earth's surface (0.03 bar) with velocity
of 14 km/s and mass of order of 1000 kg produced a pure line+molecular
band spectrum (the first component, T=5000 K) with no thermal continuum.
Numerical simulation would probably predict something else.

The mode of ablation of kilometer-size bodies remains therefore uncertain.
The observation of the end of comet SL9 may improve substantially
our knowledge in this respect, if the spectrum of the bolide were
recorded. The spectrum may be continuous or emission-line type. The
superposition of several spectra arising in different regions is possible.
If spectral lines are produced, the most hopeful line is the
H alpha at 6563 A, due to the large abundance of hydrogen in Jupiter's
atmosphere. The nearby lines of Si II at 6347 and 6371 A may be
used to study the radiation of meteoric vapors. If the temperature
exceeds 10000 K (and 30000 K seems to be quite possible), more
ionized species will radiate (N II, O II, N III, O III, Si III, Si IV,
He II).

My personal feeling is that the maximum of the brightness of the
bolides will occur higher in the Jupiter's atmosphere than predicted
in [5] and the bolides will be more luminous.

    References
    ~~~~~~~~~~
[1] Bronshten V.A.: Physics of Meteoric Phenomena, Reidel, Dordrecht (1983)
[2] Halliday I.: The spectra of meteors from Halley's comet, Astron.
    Astrophys. 187, 921-924 (1987)
[3] Borovicka J.: A fireball spectrum analysis, Astron. Astrophys.
    279, 627-645 (1993)
[4] Borovicka J.: Two components in meteor spectra, presented at the
    ACM'93 conference, Belgirate; Planet. Space Sci., in press
[5] Zahnle K. and Mac Low M.-M.: The collision of Jupiter and comet
    Shoemaker-Levy 9, Icarus, in press; available electronically

June 3, 1994

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From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 10-JUN-1994 
CC:	
Subj:	New SL9 Files

To : SL9 Mailing List

     Here is some information about the SL9 fireballs and a list of
some new files available.  Thanks to all who sent information about SL9.

<>  Dan -
<>
<> I don't know if you get specific suggestions for amateur observations, but
<> if you read our paper submitted to GRL you know that we are very interested
<> in the arrival time of the fireball above the limb of Jupiter.  I think that
<> this arrival time could be determined quite accurately if the fireball is as
<> bright as we expect it to be (if the fragments are indeed greater than 1 km),
<> especially for the impacts closest to the limb (the last couple of days).
<> Our simulations also indicate that when the fireball cools it will form a
<> debris cloud that will rise hundreds of km above the Jovian cloudtops, and
<> will enter sunlight within minutes of the impact.  The arrival time of this
<> giant cloud into sunlight would provide data on its trajectory, which in
<> turn would help us know how big the comet fragment was.  It is possible
<> that it would be big (bright) enough to be seen by amateurs.
<>
<> When I read the FAQs and the discussions on the internet I see no mention
<> of these potentially interesting and valuable observations.  I  think the
<> probability is very high that these effects will be visible for some of the
<> later impacts (e.g. W and R, visible from Hawaii, S, visible from India and
<> the far East, Q1 and Q2, visible from Africa, parts of eastern Europe and the
<> Middle East, L, Brazil and West Africa, K, South Pacific and Australia, and
<> maybe even V, on the final night, visible in the Western half of the U.S.).
<> I'd encourage the amateurs in these locations to anticipate the very real
<> possibility of seeing the fireball within tens of seconds after the impact,
<> and a few minutes later after it has cooled, condensed, and entered the
<> sunlight.
<>
<> If you would like I will send you a graph of our calculated fireball
<> trajectory plotted against line-of-sight elevations.  It can be used to
<> determine the times of arrival that can potentially be determined by
<> amateurs.
<>
<> Sincerely,
<>
<> Mark Boslough

   Here are the new files from Sandia National Laboratories that are
available at tamsun.tamu.edu (128.194.15.32) in the /pub/comet/sandia
directory. 

sandia-grl.txt    Paper involving mass and penetration depth of SL9
sandia-grl.ps     Postscript version of sandia-grl.txt
sandia-traj.ps    Graph of calculated fireball trajectory
sandia-traj.gif   GIF version of sandia-traj.ps
sandia-agu1.gif   Diagram of fragment entry; simulation
sandiafig3.gif    Figure for "sandiapaper.ps"; fireball from 3km fragment

 Also, the following files are now available in the /incoming or
/pub/comet directory: 

jun1994.moons     Jovian moon events for June 1994; eclipses, shadows, etc.
jun1994.transit   Transit Times for Red Spot and White Spots for June 1994

TRACKER2.ZIP  -  MSDOS program that displays the locations of impact sites
                 of the comet fragments for a given date and time as seen from
                 Earth.  Also shown are the locations of the Great Red Spot,
                 the white spots FA, BC, and DE.

I hope you find these files useful.

Clear skies,
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .


P.S.  If you only have email access, then I can send information about how
to obtain the files.

Note : This message was sent via the listserver [email protected].
Replying to this message could send your reply to all subscribers.  Please
send replies to [email protected] or [email protected].  Thanks.

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From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 11-JUN-1994 11:55:26.30
CC:	
Subj:	Live TV broadcast

Hello, I'm Jim Moskowitz of the Franklin Institute Science Museum.  I
was (tangentially) involved in the 'Neptune All Night' live broadcast
we did over PBS during the '89 Voyager flyby, and I've just learned
that we're going to be doing a PBS broadcast for SL9 as well. 

On Wednesday, July 20th, from 10:30 to 11:30 PM EST we'll be providing
PBS stations with a show talking about the impacts and their effects,
featuring images from Hubble, discussion with Levy and the Shoemakers,
a piece by Arthur C. Clarke, and probably much more. 

My understanding is that it will be up to the local PBS stations to
decide whether to show this program (as opposed to, maybe, an
'Eastenders' rerun). You may want to call your area station and
express interest in having the program shown in your area... 

-Jim  ([email protected])

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From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 14-JUN-1994 
CC:	
Subj:	Comet show on PBS

I forwarded the earlier message about this upcoming special on
PBS to the mailing list and newsgroup on satellite TV and I got
the following response from a PBS spokesperson.  Note that your
local PBS station will normally pick up one of the live feeds
listed below so that you will see it at 10:30-11:30 local time.
If you have a TVRO satellite dish you can watch it 5 times :-)

-----------------begin included message --------------------------

Date:         Mon, 13 Jun 1994 16:54:58 GMT
Reply-To: HOMESAT - Home Satellite Technology <[email protected]>
From: Maryanne Schuessler <[email protected]>
Organization: Public Broadcasting Service
Subject:      PBS: Great Comet Crash 7/20

As a followup to an earlier posting from Mike Gingell who forwarded
the message from Jim Moskowitz of the Franklin Institute Science
Museum about PBS coverage of the Comet Shoemaker-Levy 's collision
with Jupiter, here's what the satellite feed schedule will be --

"THE GREAT COMET CRASH"

Wednesday July 20, 1994   (into early Thursday morning 7/21)

10:30pm - 11:30pm     Telstar 401-Ku 6 (PBS Schedule B)
11:30pm - 12:30am     Telstar 401-Ku 6 (PBS Schedule B)
12:30am - 1:30 am     Telstar 401-Ku 6 (PBS Schedule B)
 1:30am - 2:30 am     Telstar 401-Ku 7 (PBS Schedule C)
 2:30am - 3:30 am     Telstar 401-Ku 5 (PBS Schedule A)
 2:30am - 3:30 am     Telstar 401-C band 8 (PBS Schedule X)

Also on the PBS schedules that night, "MISSIONS TO THE MOON" and
"APOLLO 13: TO THE EDGE AND BACK."    It should be quite a night.

--
Maryanne Schuessler
Broadcast Operations Department, Public Broadcasting Service
Alexandria, Virginia 22314

----------------------end of included message ----------------------

Mike,  [email protected]    Raleigh, NC USA, (919) 850-6444 (day)

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From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 14-JUN-1994 
CC:	
Subj:	Comet/Jupiter Collision FAQ

To : SL9 Mailing List

     We will try to use the newsgroup "alt.com" for more discussions
of the collision of comet Shoemaker-Levy 9 with Jupiter since there is
probably not enough time to make a new newsgroup. 

     Also, there is a gathering of professional and amateur
astronomers every week on the IRC (Internet Relay chat) channel
#Astronomy for real time discussions.  Friday and Sunday sessions are
held at 20:00 UT. 

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

                     Frequently Asked Questions about
          the Collision of Comet Shoemaker-Levy 9 with Jupiter

                        Last Updated 14-Jun-1994
                            32 Days to Impact

    The following is a list of answers to frequently asked questions
concerning the collision of comet Shoemaker-Levy 9 with Jupiter.  Thanks
to all those who have contributed.  Contact Dan Bruton ([email protected])
or John Harper ([email protected]) with comments, additions, corrections,
etc.  A PostScript version and updates of this FAQ list are available via
anonymous ftp to tamsun.tamu.edu (128.194.15.32) in the /pub/comet
directory.  To subscribe to the "Comet/Jupiter Collision Mailing List",
send mail to [email protected] (no subject) with the message:
SUBSCRIBE SL9 Firstname Lastname.

RECENT CHANGES TO THIS FAQ LIST

        Question 1.1: Limb Crossing Times
        Question 1.3: HST March images
        Question 1.4: More predictions
        Question 2.1: Updated impact times and impact locations
        Question 2.3: Galilean satellite eclipses
        Question 2.4: Updated orbital parameters of the comet
        Question 2.5: Images of crater chains
       Question 2.10: Mail access to files
          REFERENCES: New Journal Articles

GENERAL QUESTIONS

 Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 Q1.2: Who are Shoemaker and Levy?
 Q1.3: Where can I find a GIF image of this comet?
 Q1.4: What will be the effects of the collision?
 Q1.5: Can I see the effects in my telescope?

SPECIFICS

Q2.1: What are the impact times and impact locations?
Q2.2: Can the collisions be observed with radio telescopes?
Q2.3: Will light from the explosions be reflected by any moons?
Q2.4: What are the orbital parameters of the comet?
Q2.5: Why did the comet break apart?
Q2.6: What are the sizes of the fragments?
Q2.7: How long is the fragment train?
Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?
Q2.9: To whom can I report my observations?
Q2.10: Where can I find more information?

REFERENCES
ACKNOWLEDGMENTS

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

GENERAL QUESTIONS

Q1.1: Is it true that a comet will collide with Jupiter in July 1994?

     Yes, the shattered comet Shoemaker-Levy 9 (1993e) is expected to
collide with Jupiter over a 5.6 day period in July 1994.  The first of 21
comet fragments is expected to hit Jupiter on July 16, 1994 and the last on
July 22, 1994.  The 21 major fragments are denoted A through W in order of
impact, with letters I and O not used.  All of the comet fragments will hit
on the dark farside of Jupiter.  The probability that all of the comet
fragments will hit Jupiter is greater that 99.9%.  The probability that any
fragment will impact on the near side as viewed from the Earth is < 0.01%.
     The impact of the center of the comet train is predicted to occur at a
Jupiter latitude of about -44 degrees at a point about 67 degrees east
(toward the sunrise terminator) from the midnight meridian.  These impact
point estimates from Chodas and Yeomans are only 5 to 9 degrees behind the
limb of Jupiter as seen from Earth.  About 8 to 18 minutes after each
fragment hits, the impact points will rotate past the limb.  The impact
sites of the later fragments are closer to the limb and will therefore
rotate into view sooner after impact.  After these points cross the limb it
will take another 18 minutes before they cross the morning terminator into
sunlight.


Q1.2: Who are Shoemaker and Levy?

     Eugene and Carolyn Shoemaker and David H. Levy found the 13.8 magnitude
comet on photographic plates taken on March 24, 1993.  The photographs were
taken at Palomar Mountain in Southern California with a 0.46 meter Schmidt
camera and were examined using a stereomicroscope to reveal the comet [2,14].
James V. Scotti confirmed their discovery with the Spacewatch Telescope at
Kitt Peak in Arizona.  See [11] for more information about the discovery.


Q1.3: Where can I find a GIF image of this comet?

     GIF images can be obtained from SEDS.LPL.Arizona.EDU (128.196.64.66)
in the /pub/astro/SL9/images directory.  Below is a list of the images at
this site.  The files are listed here in reverse chronological order:

Comet1993eA.gif    March HST image of SL9 comet train
Comet1993eB.gif    Time comparison image of SL9 comet fragment
sl90216.gif        February 16, 1994 Image from Kitt Peak (J. Scotti)
wfpclevy.gif       Photo Montage of January 24-27 Imaging of SL9 from HST
sl9hst.gif         Post-fix HST Mosaic of SL9 (Jan. 24-27)
sl90121.gif        January 21, 1994 Image from Kitt Peak (R. Jedicke)
sl9compl.gif       Six month comparison image of SL9
1993eha.gif        View of the comet from HST
1993ehb.gif        From HST, focused on the center of the train of fragments
1993esw.gif        Ground-based view of the comet
sl03302b.gif       March 30, 1993 Image from Kitt Peak (J. Scotti)
sl9_930330.gif     March 30, 1993 image of SL9, Spacewatch, J. Scotti
sl9w_930328.gif    March 28, 1993 image of SL9
shoelevy.gif       An early GIF image of SL9

     The following is a list of other collision related GIF graphics and
MPEG animations that are also available at SEDS.LPL.Arizona.EDU:

gipul.gif          Gipul Catena crater chain on Jupiter's moon, Callisto
chain.gif          Crater Chain on Jupiter's Moon, Callisto
orbtrain.gif       SL9's orbit showing the length of the train
schematic2.gif     Diagram of fragment positions as seen from HST; Mar'94
schematic1.gif     Diagram of fragment positions as seen from HST; Jan'94
approach.gif       View of last 18 hours of trajectory, from Earth
earthview.gif      Full-disk view from Earth
earthviewzoom.gif  Close-up view from Earth
vgr2view.gif       Full-disk view from Voyager 2
vgr2viewzoom.gif   Close-up view of impact sites from direction of Voyager 2
galview.gif        View from Galileo
ulysview.gif       View from Ulysses
poleview.gif       View from beneath Jupiter
orbjupplane.gif    SL9's orbit projected into Jupiter's orbit plane
orbsun.gif         SL9's orbit as seen from the Sun
earthjup.gif       Jupiter-Facing Hemispheres of Earth at Impact Times of SL9
impact.gif         Graph of impact times with moon eclipses
index.gif          Mosaic of some of the images in this directory
mitwave1.gif       Frame from MIT Flow Visualization Lab. Simulation
mitwave2.gif       Frame from MIT Flow Visualization Lab. Simulation
mitwave.mpg        MIT Flow Visualization Lab. Simulation Animation
vidjv.mpg          Animation of SL9 entering Jupiter's Atmosphere
visejz.mpg         Animation of explosion produced by SL9 entering Jupiter
sl9rend.gif        Rendering 3 views of comet-Jupiter collision
sl9rend1.gif       Larger rendering comet-Jupiter from Earth
sl9rend2.gif       Larger rendering comet-Jupiter from Voyager 2
sl9rend3.gif       Larger rendering comet-Jupiter from south pole


Q1.4: What will be the effects of the collision?

     As seen from the Earth, the fragments will disappear behind the limb of
Jupiter only 5 to 15 seconds before impact.  The later fragments will be
visible closer to impact.  Fragment W will disappear only 5 seconds before
impact, at an altitude of only about 200 km above the 1-bar pressure level:
it may well start its bolide phase while still in view.  Furthermore, any
sufficiently dense post-impact plume will have to rise only a few hundred
kilometers to be visible from Earth.
     Simulations by Mark Boslough and others indicate that when the fireball
resulting from an impact cools it will form a debris cloud that will rise
hundreds of kilometers above the Jovian cloudtops, and will enter sunlight
within minutes of the impact.  The arrival time of this giant cloud into
sunlight would provide data on its trajectory, which in turn would help us
know how big the comet fragment was.  It is possible that it would be big
(bright) enough to be seen by amateurs [42,43].  Mark Boslough of Sandia
National Laboratories also states that the probability is very high that
these effects will be visible for some of the later impacts (e.g. W and R,
visible from Hawaii, S, visible from India and the far East, Q1 and Q2,
visible from Africa, parts of eastern Europe and the Middle East, L, Brazil
and West Africa, K, South Pacific and Australia, and maybe even V, on the
final night, visible in the Western half of the U.S.).  Observers in these
locations are encouraged to anticipate the possibility of seeing the fireball
within tens of seconds after the impact, and a few minutes later after it has
cooled, condensed, and entered the sunlight.
     Jupiter will be about 770 million kilometers (480,000,000 miles) from
Earth, so it will be difficult to see the effects from Earth.  Also,
the comet fragments will not effect Jupiter as a whole very much.  It will
be like sticking 21 needles into an apple: "Locally, each needle does
significant damage but the whole apple isn't really modified very much." [35].
The energy deposited by the comet fragments fall well short of the energy
required to set off sustained thermonuclear fusion.  Jupiter would have to
be more than 10 times more massive to sustain a fusion reaction.
     Each comet fragment will enter the atmosphere at a speed of 130,000 mph
(60 km/s).  At an altitude of 100 km above the visible cloud decks,
aerodynamic forces will overwhelm the material strength of the comet,
beginning to squeeze it and tear it apart.  Five seconds after entry, the
comet fragment will deposit its kinetic energy of around 10^28 ergs
(equivalent to around 200,000 megatons of TNT) at 100-150 km below the
cloud layer [19].  Bigger fragments will have more energy and go deeper.
     The hot (30,000 K) gas resulting from the stopped comet will explode,
forming a fireball similar to a nuclear explosion, but much larger.
The visible fireball may only rise 100 km or so above the cloudtops.
Above that height the density may drop so that it will become transparent.
The fireball material will continue to rise, reaching a height of perhaps
1000 km before falling back down to 300 km.  The fireball will spread out
over the top of the stratosphere to a radius of 2000-3000 km from the point
of impact (or so the preliminary calculations say).  The top of the resulting
shock wave will accelerate up out of the Jovian atmosphere in less than two
minutes, while the fireball will be as bright as the entire sunlit surface of
Jupiter for around 45 sec [18].  The fireball will be somewhat red, with a
characteristic temperature of 2000 K - 4000 K (redder than the sun, which is
5800 K).  Virtually all of the shocked cometary material will rise behind the
shock wave, leaving the Jovian atmosphere and then splashing back down on top
of the stratosphere at an altitude of 300 km above the clouds [unpublished
simulations by Mac Low & Zahnle].  Not much mass is involved in this splash,
so it will not be directly observable.  The splash will be heavily enriched
with cometary volatiles such as water or ammonia, and so may contribute to
significant high hazes.
        Meanwhile, the downward moving shock wave will heat the local clouds,
causing them to buoyantly rise up into the stratosphere.  This will allow
spectroscopists to attempt to directly study cloud material, a unique
opportunity to confirm theories of the composition of the Jovian clouds.
Furthermore, the downward moving shock may drive seismic waves (similar to
those from terrestrial earthquakes) that might be detected over much of the
planet by infrared telescopes in the first hour or two after each impact.
The strength of these two effects remains a topic of research.  The
disturbance of the atmosphere will drive internal gravity waves ("ripples in
a pond") outwards.  Over the days following the impact, these waves will
travel over much of the planet, yielding information on the structure of
the atmosphere if they can be observed (as yet an open question).
     The "wings" of the comet will interact with the planet before and after
the collision of the major fragments.  The so-called "wings" are defined to
be the distinct boundary along the lines extending in both directions from
the line of the major fragments; some call these 'trails'.  Sekanina, Chodas
and Yeomans have shown that the trails consist of larger debris, not dust:
5-cm rock-sized material and bigger (boulder-sized and building-sized).
Dust gets swept back above (north) of the trail-fragment line due to solar
radiation pressure.  The tails emanating from the major fragments consist of
dust being swept in this manner.  Only the small portion of the eastern
debris trail nearest the main fragments will actually impact Jupiter,
according to the model, with impacts starting only a week before the major
impacts.  The western debris trail, on the other hand, will impact Jupiter
over a period of months following the main impacts, with the latter portion
of the trail actually impacting on the front side of Jupiter as viewed from
Earth.
        The injection of dust from the wings and tail into the Jovian system
may have several consequences.  First, the dust will absorb many of the
energetic particles that currently produce radio emissions in the Jovian
magnetosphere.  The expected decline and recovery of the radio emission may
occur over as long as several years, and yield information on the nature and
origin of the energetic particles.  Second, the dust may actually form a
second faint ring around the planet.


Q1.5: Can I see the effects in my telescope?

     One might be able to detect atmospheric changes on Jupiter using
photography or CCD imaging.  It is important, however, to observe Jupiter
for several months in advance in order to know which features are due to
impacts and which are naturally occurring.  It appears more and more likely
that most effects will be quite subtle.  Without a large ( > 15" ?) telescope
and good detector, little is likely to be seen.
     It is possible that the impacts may create a new, temporary storm at the
latitude of the impacts.  Modeling by Harrington et al. suggests this is
possible [30].  The fragments of comet Shoemaker-Levy 9 will strike just
south of the South South Temperate Belt of Jupiter.  If the nuclei penetrate
deep enough, water vapor may shoot high into the atmosphere where it could
turn into a bluish shroud over a portion of the South South Temperate Zone
[31].
     Impacts of the largest fragments may create one or two features.  A spot
might develop that could be a white or dark blue nodule and would likely have
a maximum diameter of 2,000 km to 2,500 km which in a telescope would be 1
to 1.5 arcseconds across.  This feature would be very short-lived with the
impact site probably returning to normal after just a few rotations of
Jupiter.  A plume might also develop that would look dark against the South
Temperate Zone's white clouds or could appear as a bright jet projected from
Jupiter limb [31].  The table below shows the approximate sizes of features
that already exist on Jupiter for comparison.

 +====================================================================+
 |          FEATURE                            SIZE ESTIMATES         |
 +====================================================================+
 |       Great Red Spot                       29000 by 12000 km [32]  |
 |     White Spots FA,BC,DE                   7500 by 3000 km         |
 |  Shadows of Io, Europa, and Ganymede       4300, 4200, 7100 km     |
 +====================================================================+

     Below is a list of files available at tamsun.tamu.edu in the /pub/comet
directory that may be helpful in identifying features on Jupiter:

tracker2.zip      MSDOS program that displays the location of impact sites
jupe.description  Description of a PC program showing features of Jupiter
jun1994.transit   Transit Times for Red Spot and White Spots for May 1994
jun1994.moons     Jovian Moon events for May 1994 (Shadows, Eclipses, etc.)

    Also, there are little anticyclonic ovals at latitudes of about -41
degrees which are typical of the South South Temperate domain.  There are
usually 6 or 7 around the planet and they move with the South South
Temperate current, i.e. faster than BC and DE.  See Sky & Telescope
for a photo of these ovals by Don Parker [38].


* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *


SPECIFICS

Q2.1: What are the impact times and impact locations?

This information was provided P.W. Chodas and D.K. Yeomans:
============================================================================
Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
P.W. Chodas and D.K. Yeomans (JPL/Caltech)
Predictions as of 1994 June 3
Date of last astrometric data in these solutions: 1994 June 1

Immediately to the right of the predicted impact times, we give the 1-sigma
uncertainties in those times for all fragments except Q2.  We have made an
effort to make these uncertainties realistic: they are not formal uncertainty
values.  NOTE: To obtain a 95% confidence level, one should use a +/- 2 sigma
window around the predicted impact time.  The uncertainties for fragment Q2
have not been quantified, but are probably comparable to those for P2.

The dynamical model used for the predictions includes perturbations due to
the Sun, planets, Galilean satellites and the oblateness of Jupiter.  The
planetary ephemeris used was DE245.

----------------------------------------------------------------
Fragment   Impact   1-sig   Jovicentric   Meridian  Angle
          Date/Time  Unc.   Lat.   Long.   Angle    E-J-F   Orbit
         July  (UT) (min)   (deg)  (deg)   (deg)    (deg)    Ref.
---------------h--m---------------------------------------------
 A = 21   16  19:55   26   -43.23   176    63.56    99.35    A10
 B = 20   17  03:07   23   -43.45    77    63.67    99.22    B11
 C = 19   17  06:59   24   -43.33   217    64.53    98.64    C8
 D = 18   17  11:18   28   -43.34    14    63.49    99.36    D9
 E = 17   17  15:30   17   -43.70   164    66.13    97.41    E25
 F = 16   18  00:40   23   -43.79   139    64.17    98.77    F16
 G = 15   18  07:52   16   -43.80    37    66.99    96.77    G25
 H = 14   18  19:47   16   -43.86   109    67.32    96.52    H23
 K = 12   19  10:39   16   -43.96   287    68.15    95.90    K24
 L = 11   19  22:40   16   -44.07     2    68.95    95.31    L25
 N = 9    20  10:21   26   -44.59    67    67.13    96.49    N12
 P2= 8b   20  15:27   25   -44.82   253    66.46    96.91    P11
 Q2= 7b   20  19:49        -44.48    48    69.27    95.00
 Q1= 7a   20  20:16   15   -44.20    64    69.69    94.75    Q27
 R = 6    21  05:59   19   -44.27    57    70.24    94.34    R22
 S = 5    21  15:46   17   -44.26    51    70.76    93.97    S32
 T = 4    21  18:16   44   -45.28   145    67.43    96.14    T7
 U = 3    22  00:25   85   -45.19     3    71.74    93.15    U6
 V = 2    22  04:06   31   -44.52   141    68.16    95.77    V8
 W = 1    22  08:34   19   -44.29   299    71.32    93.57    W25


Notes:
1. Fragments J=13 and M=10 are omitted because they have faded from view.
   Fragments P=8 and Q=7 each consist of multiple components.  The March'94
   HST image shows that P1=8a has almost completely faded away (so it too is
   omitted from the Table), and that P2=8b has split.  We do not as yet
   have sufficient data to obtain independent predictions for the two
   components of P2=8b.

2. The impact date/time is the time the impact would be seen at the Earth
   (if the limb of Jupiter were not in the way); the date is the day in
   July 1994; the time is given as hours and minutes of Universal Time.

3. The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

4. The impact longitude is in System II, measured westwards on the planet.

5. The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.  This relative
   longitude is known much more accurately than the absolute longitude.

6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact.  All impacts will be just on the
   farside as viewed from Earth; later impacts are closer to the limb.

7. The angle of incidence of the impacts is between 41 and 42 degrees
   for all the fragments.

============================================================================

     See "impacts.*" at SEDS.LPL.Arizona.EDU in the /pub/astro/SL9/info
directory for updates and more details about these predictions.  The
following are the 1-sigma (uncertainty) predictions for the fragment impact
times:
               on March 1         -  30 min
               on May 1           -  24 min
               on June 1          -  16 min
               on July 1          -  10 min
               on July 15         -   6 min
               at impact - 18 hr  -   3 min

The time between impacts is thought to be known with more certainty than the
actual impact times.  This means that if somehow the impact time of the first
fragment can be measured experimentally, then impact times of the fragments
that follow can be predicted with more accuracy.


Q2.2: Can the collision be observed with radio telescopes?

     The cutoff of radio emissions due to the entry of cometary dust into the
Jovian magnetosphere during the weeks around impact may be clear enough to be
detected by small radio telescopes.  Furthermore, impacts may be directly
detectable in radio frequencies.  Some suggest to listen in on 15-30 MHz
during the comet impact.  So it appears that one could use the same antenna
for both the Jupiter/Io phenomenon and the Jupiter/comet impact.  There is
an article in Sky & Telescope magazine which explains how to build a simple
antenna for observing the Jupiter/Io interaction [4,24,25].
     For those interested in radio observations during the SL9 impact,
Leonard Garcia of the University of Florida has made some information
available.  The following files are available via anonymous ftp on the
University of Florida, Department of Astronomy site astro.ufl.edu in the
/pub/jupiter directory:

  README.DOC      Explanation of predicted Jupiter radio storms tables
  jupradio.txt    Jovian Decametric Emission and the SL9/Jupiter Collision
  jupradio.ps     Postscript version of jupradio.txt
  hist.ps         Histogram of occurrence probabilities of Jupiter radio
                        emission at different frequencies.
  may94.txt       Tables of predicted Jupiter radio storms for May 1994
  june94.txt      Tables of predicted Jupiter radio storms for June 1994
  july94.txt      Tables of predicted Jupiter radio storms for July 1994

    The antenna required to observe Jupiter may be as simple as a dipole
antenna constructed with two pieces of wire 11 feet 8.4 inches in length,
connected to a 50 ohm coax cable.  This antenna should be laid out on a
East-West line and raised above the ground by at least seven feet.  A
Directional Discontinuity Ring Radiator (DDRR) antenna is also easy to
construct and can be made from 1/2 inch copper tubing 125.5 inches in
length (21Mhz).   The copper tube should be bent into a loop and placed 5
inches above a metallic screen.   A good preamp is required for
less sensitive shortwave receivers [39].


Q2.3: Will light from the explosions be reflected by any moons?

     One may be able to witness the collisions indirectly by monitoring the
brightness of the Galilean moons that may be behind Jupiter as seen from
Earth.  One could monitor the moons using a photometer, a CCD camera, or a
video camera.  However, current calculations suggest that the brightenings
may be as little as 0.05% of the sunlit brightness of the moon [18].  If a
moon can be caught in eclipse but visible from the earth during an impact,
prospects will improve significantly.  According to current predictions,
the only impact certain to occur during a satellite eclipse is K=12 with
Europa eclipsed.  However, H=14 and W=1 impact only about 2 sigma after Io
emerges from eclipse at longitude 20 deg, and B=20, E=17 and F=16 impact
0.5-2 sigma after Amalthea emerges from eclipse at longitude 34 deg.
     The following files contain information concerning the reflection of
light by Jupiter's moons and are available at SEDS.LPL.Arizona.EDU :

galsat52.zip      MSDOS Program that Displays relative positions of
                      Jupiter's Moons during times of impact
impact_24apr.ps   PostScript Plot of impact times at satellite availability
jsat8.*           Jovian satellite locations

The following information was provided by John Spencer, 11 Apr 1994:
===========================================================================

COMET IMPACT SATELLITE REFLECTIONS

Here's an updated table of satellite reflector availability, based on
the latest (1994/02/23) Chodas and Yeomans ephemerides.  Times haven't
changed much but uncertainties have gone down.  No impact times are yet
available for P1=8a and Q2=7b.

In the table, a "+" next to the orbital longitude means that the
impact will be visible from the satellite.  Longitudes greater than 90
degrees will be less useful as the phase angle of the reflected light
(to first order, equal to the longitude) will be high and its
brightness will be greatly reduced.  An "e" means the satellite will
be visible in eclipse, allowing higher sensitivity observations, and
an "o" means it will be occulted by Jupiter.  I've included Callisto
(J4) for completeness but it's likely to be too far out to be useful-
the same may be true for Ganymede (J3).

---------------------------------------------------------
          UT               Satellite Orbital Longitudes
        date of  Bright    (degrees past superior conj.)
        impact   -ness  ---------------------------------
Nucleus (July)   Index   J5     J1     J2     J3     J4
---------------------------------------------------------
  A=21  16.81      1    193    340    103+    75+    35+
  B=20  17.11      1     50+    41+   133+    90+    42+
  C=19  17.27      1    165     74+   149+    98+    45+
  D=18  17.48      1    317    116+   171    109+    50+
  E=17  17.61      2     51+   143+   184    116+    52+
  F=16  18.02      2    347o   226    225    136+    61+
  G=15  18.30      3    190    283    254    150+    67+
  H=14  18.78      3    177     21+   302    174     78+
  K=12  19.42      3    279    151+     7e   207     91+
  L=11  19.89      3    259    246     55+   230    101+
   N=9  20.41      1    274    352o   107+   256    113+
 P2=8b  20.61      2     59+    33+   128+   266    117+
 P1=8a             1
 Q2=7b             2
 Q1=7a  20.80      3    196     72+   147+   276    121+
   R=6  21.28      2    183    169+   196    300    131+
   S=5  21.61      3     61+   236    229    317    138+
   T=4  21.75      1    162    265    243    324    141+
   U=3  21.88      1    256    291    256    330    144+
   V=2  22.18      2    113+   352o   287    345    151+
   W=1  22.32      2    214     21+   301    352+   154+
Uncertainties (1-sigma):
         0.03      1     22      6      3    1.5      1
---------------------------------------------------------

The "brightness index" subjectively rates comet fragment
brightnesses, 3 being brightest. Brightnesses are eyeballed from
the press-released HST image where possible and are different from
those in previous versions of the table.

There's a good chance that reflections from the impact of the bright
fragment K=12 will be visible off Europa in eclipse, very close to
Jupiter: this impact can be seen in a dark sky from Australia, New
Zealand, and Hawaii.

Given the uncertainties, there's nearly a 50% chance that the impact
of either H=14 (a bright fragment) or W=1 will be seen reflected off Io
in eclipse.  The H=14 impact will be visible in darkness from East and
South Africa, and the middle East, the W=1 impact from New Zealand and
Hawaii.

The table below gives the orbital longitudes (in degrees) of
satellites when in Jupiter eclipse and occultation (used to annotate
the above table).  Values should be good to about one degree.

-------------------------------------
Satellite       Occulted   Eclipsed
-------------------------------------
J5: Amalthea   337 - 023  023 - 034
J1: Io         351 - 009  009 - 020
J2: Europa     355 - 005  005 - 016
J3: Ganymede   358 - 002  009 - 013
J4: Callisto   No occultations or eclipses
------------------------------------

     See "satellites.*" at SEDS.LPL.Arizona.EDU in the /pub/astro/SL9/info
directory for updates.

===========================================================================

     Also, monitoring the eclipses of the Galilean satellites after the
impacts may yield valuable scientific data with the moons serving as
sensitive probes of any cometary dust in Jupiter's atmosphere.  The geometry
of the eclipses is such that the satellites pass through the shadow at
roughly the same latitude as the predicted comet impacts.  There is an
article in the first issue of CCD Astronomy involving these observations.
The article says that if the dust were to obscure sunlight approximately
120 kilometers above Jupiter's cloud tops, Io could be more that 3 percent
(0.03 magnitudes) fainter than normal at mideclipse [40].


Q2.4: What are the orbital parameters of the comet?

     Comet Shoemaker-Levy 9 is actually orbiting Jupiter, which is most
unusual: comets usually just orbit the Sun.  Only two comets have ever been
known to orbit a planet (Jupiter in both cases), and this was inferred in
both cases by extrapolating their motion backwards to a time before they
were discovered.  S-L 9 is the first comet observed while orbiting a planet.
Shoemaker-Levy 9's previous closest approach to Jupiter (when it broke up)
was on July 7, 1992; the distance from the center of Jupiter was about
96,000 km, or about 1.3 Jupiter radii.  The comet is thought to have reached
apojove (farthest from Jupiter) on July 14, 1993 at a distance of about 0.33
Astronomical Units from Jupiter's center.  The orbit is very elliptical,
with an eccentricity of over 0.998.  Computations by Paul Chodas, Zdenek
Sekanina, and Don Yeomans, suggest that the comet has been orbiting Jupiter
for 20 years or more, but these backward extrapolations of motion are highly
uncertain.  See "elements.*" and "ephemeris.*" at SEDS.LPL.Arizona.EDU in
/pub/astro/SL9/info for more information.
     In the abstract "The Orbit of Comet Shoemaker-Levy 9 about Jupiter"
by D.K. Yeomans and P.W. Chodas (1994, BAAS, 26, 1022), the elements
for the brightest fragment Q are listed.  These elements are Jovicentric
and for Epoch 1994Jul15 (J2000 ecliptic):

1994 Periapses      Jul 20.7846
Eccentricity        0.9987338
Periapses dist.     34776.7 km
Arg. of periapses   43.47999
Long. of asc. node  290.87450
inclination         94.23333


Q2.5: Why did the comet break apart?

     The comet broke apart due to tidal forces on its closest approach to
Jupiter (perijove) on July 7, 1992 when it passed within the theoretical
Roche limit of Jupiter.  Shoemaker-Levy 9 is not the first comet observed
to break apart.  Comet West shattered in 1976 near the Sun [3].  Astronomers
believe that in 1886 Comet Brooks 2 was ripped apart by tidal forces near
Jupiter [2].  Several other comets have also been observed to have split
[41].
     Furthermore, images of Callisto and Ganymede show crater chains which
may have resulted from the impact of a shattered comet similar to Shoemaker-
Levy 9 [3,17].  The satellite with the best example of aligned craters is
Callisto with 13 crater chains.  There are three crater chains on Ganymede.
These were first thought to be from basin ejecta; in other words secondary
craters.  See Q1.3 and [27] for images of crater chains.
     There are also a few examples of crater chains on our Moon.  Jay Melosh
and Ewen Whitaker have identified 2 possible crater chains on the moon which
would be generated by near-Earth tidal breakup.  One is called the "Davy
chain" and it is very tiny but shows up as a small chain of craters aligned
back toward Ptolemaeus.  In near opposition images, it appears as a high
albedo line; in high phase angle images, you can see the craters themselves.
The second is between Almanon and Tacitus and is larger (comparable to the
Ganymede and Callisto chains in size and length).


Q2.6: What are the sizes of the fragments?

     Using measurements of the length of the train of fragments and a model
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the
parent nucleus of the comet (before breakup) was only about 2 km across [13].
This would imply that the individual fragments are no larger than about 500
meters across.  Images of the comet taken with the Hubble Space Telescope in
July 1993 indicate that the fragments are 3-4 km in diameter (3-4 km is an
upper limit based on their brightness).  A more elaborate tidal disruption
model by Sekanina, Chodas and Yeomans [20] predicts that the original comet
nucleus was at least 10 km in diameter.  This means the largest fragments
could be 3-4 km across, a size consistent with estimates derived from the
Hubble Space Telescope's July 1993 observations.
     The new images, taken with the Hubble telescope's new Wide Field and
Planetary Camera-II instrument on January 24-27, 1994, have given us an even
clearer view of this fascinating object, which should allow a refinement of
the size estimates.  In addition, the new images show strong evidence for
continuing fragmentation of some of the remaining nuclei, which will be
monitored by the Hubble telescope over the next month.


Q2.7: How long is the fragment train?

     The angular length of the train was about 51 arcseconds in March 1993
[2].  The length of the train then was about one half the Earth-Moon
distance.  In the day just prior to impact, the fragment train will stretch
across 20 arcminutes of the sky, more that half the Moon's angular diameter.
This translates to a physical length of about 5 million kilometers.  The
train expands in length due to differential orbital motion between the first
and last fragments.  Below is a table with data on train length based on
Sekanina, Chodas, and Yeomans's tidal disruption model:

           +=============================================+
           |    Date    Angular Length  Physical Length  |
           |               (arcsec)          (km)        |
           +=============================================+
           |  93 Mar 25       49            158,000      |
           |     Jul  1       67            265,000      |
           |  94 Jan  1      131            584,000      |
           |     Feb  1      161            669,000      |
           |     Mar  1      200            762,000      |
           |     Apr  1      255            893,000      |
           |     May  1      319          1,070,000      |
           |     Jun  1      400          1,366,000      |
           |     Jul  1      563          2,059,000      |
           |     Jul 15      944          3,593,000      |
           |    Impact A    1286          4,907,000      |
           +=============================================+


Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?

     The Hubble Space Telescope, like earthlings, will not be able to see the
collisions but will be able to monitor atmospheric changes on Jupiter.  The
new impact points are more favorable for viewing from spacecraft: it can now
be stated with certainty that the impacts will all be visible to Galileo,
and now at least some impacts will be visible to Ulysses.  Although Ulysses
does not have a camera, it will monitor the impacts at radio wavelengths.
        Galileo will get a direct view of the impacts rather than the grazing
limb view previously expected.  The Ida image data playback is scheduled to
end at the end of June, so there should be no tape recorder conflicts with
observing the comet fragments colliding with Jupiter.  The problem is how to
get the most data played back when Galileo will only be transmitting at 10
bps.  One solution is to have both Ulysses and Galileo record the event and
and store the data on their respective tape recorders.  Ulysses observations
of radio emissions data will be played back first and will at least give
the time of each comet fragment impact.  Using this information, data can
be selectively played back from Galileo's tape recorder.  From Galileo's
perspective, Jupiter will be 60 pixels wide and the impacts will only show
up at about 1 pixel, but valuable science data can still collected in the
visible and IR spectrum along with radio wave emissions from the impacts.
     The impact points are also viewable by both Voyager spacecraft,
especially Voyager 2.  Jupiter will appear as 2.5 pixels from Voyager 2's
viewpoint and 2.0 pixels for Voyager 1.  However, it is doubtful that the
Voyagers will image the impacts because the onboard software that controls
the cameras has been deleted, and there is insufficient time to restore and
test the camera software.  The only Voyager instruments likely to observe
the impacts are the ultraviolet spectrometer and planetary radio astronomy
instrument.  Voyager 1 will be 52 AU from Jupiter and will have a near-limb
observation viewpoint.  Voyager 2 will be in a better position to view the
collision from a perspective of looking directly down on the impacts, and
it is also closer at 41 AU.


Q2.9: To whom can I report my observations?

     Observation forms by Steve Lucas are available via ftp at
oak.oakland.edu in the /pub/msdos/astrnomy directory.  These forms also
contain addresses of "Jupiter Watch Program" section leaders.  jupcom02.zip
contains Microsoft Write files.  The Association of Lunar and Planetary
Observers (ALPO) will also distribute a handbook to interested observers.
The handbook "The Great Crash of 1994" is available for $10 by

                        ALPO Jupiter Recorder
                        Phillip W. Budine
                        R.D. 3, Box 145C
                        Walton, NY 13856 U.S.A.

The cost includes printing, postage and handling.
     John Rogers, the Jupiter Section Director for the British Astronomical
Association, will be collecting data from regular amateur Jupiter observers
in Britain and worldwide.  He can be reached via email ([email protected])
or fax (UK [223] 333840).  For other addresses see page 44 of the January
1994 issue of Sky & Telescope magazine [14].


Q2.10: Where can I find more information?

   The SL9 educator's book put out by JPL is in the /pub/astro/SL9/EDUCATOR
directory of SEDS.LPL.Arizona.edu.  There are two technical papers [18,19]
on the atmospheric consequences of the explosions available at
oddjob.uchicago.edu in the /pub/jupiter directory.  There are some
PostScript images and text files involving the results of fireball simulations
by Sandia National Laboratories at tamsun.tamu.edu (128.194.15.32) in the
/pub/comet/sandia directory.
    SEDS (Students for the Exploration and Development of Space) has set up
an anonymous account which allows you to use "lynx" - a VT100 WWW browser.
To access this service, telnet to SEDS.LPL.Arizona.EDU and login as "www"
(no password required).  This will place you at the SEDS home page, from
which you can select Shoemaker-Levy 9.  A similar "gopher" interface is
available at the same site.  Just login as "gopher".
     Below is a list of FTP and WWW sites with SL9 information:

===============================================================================
   FTP SITE NAME       IP ADDRESS       DIRECTORY                   CONTENTS
===============================================================================
SEDS.LPL.Arizona.EDU (128.196.64.66)  /pub/astro/SL9             Images & Info
jwd.ping.de                           /pub/people/hh/astro/comet   SEDS Mirror
oddjob.uchicago.edu                   /pub/jupiter                   Articles
jplinfo.jpl.nasa.gov (137.78.104.2)   /news and /images              Images
ftp.cicb.fr          (129.20.128.34)  /pub/Images/ASTRO/hst          Images
tamsun.tamu.edu      (128.194.15.32)  /pub/comet                 Images & Info

===============================================================================
     WORLD WIDE WEB SITES                                           CONTENTS
===============================================================================
http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html      Info & Images
http://seds.lpl.arizona.edu/sl9/sl9.html                          Images & Info
http://pscinfo.psc.edu/research/user_research/user_research.html  Animations

     If you have only mail access then try emailing the following message
(no subject) to [email protected]:

ftp SEDS.LPL.Arizona.EDU
user anonymous guest
cd pub
cd astro
cd SL9
dir
cd info
get factsheet.txt

The file "factsheet.txt" should then be mailed to your account.  Other files
can be retrieved in a similar manner.  For more info email the following
message to [email protected]:

help
howtoftp

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

REFERENCES

[1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
[2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
      page 38-39.
[3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
      chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
[4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
[5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
[6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
[7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
[8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
      September 1993, page 18.
[9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
[10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
[11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
[12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
      of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
[13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
      Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
[14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
      January 1994, page 40-44.
[15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
[16] "AstroNews", Astronomy, January 1994, page 19.
[17] "AstroNews", Astronomy, February 1994, page 16.
[18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
      Comet Shoemaker Levy 9", submitted to Icarus October 29, 1993.
[19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
      Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
      submitted to Science on 10 February 1994.
[20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the
     Appearance of Periodic Comet Shoemaker-Levy 9", Astronomy &
     Astrophysics, in press.
[21] "On a collision Course with Jupiter", Mercury, Nov-Dec 1993, page 15-16.
[22] "Timing the Crash", Sky & Telescope, February 1994, page 11.
[23] "Capturing Jupiter on Video" Sky & Telescope, September 1993, page 102.
[24] North, Gerald, "Advanced Amateur Astronomy", page 296-298, (1991).
[25] "Backyard Radio Astronomy", Astronomy, March 1983, page 75-77.
[26] Harrington, J., R. P. LeBeau, K. A. Backes, and T. E. Dowling,
     "Dynamic response of Jupiter's atmosphere to the impact of comet
     Shoemaker-Levy 9" Nature 368: 525-527 (1994).
[27] David Morrison, "Satellites of Jupiter", page 392, (1982).
[28] Weaver, H. A., P. D. Feldman, M. F. A'Hearn, C. Arpigny, R. A. Brown,
     E. F. Helin, D. H. Levy, B. G. Marsden, K. J. Meech, S. M. Larson,
     K. S. Knoll, J. V. Scotti, Z. Sekanina, C. S. Shoemaker, E. M. Shoemaker,
     T. E. Smith, A. D. Storrs, D. K. Yeomans, and B. Zellner,
     "Hubble Space Telescope Observations of Comet P/Shoemaker-Levy 9 (1993e)."
     Science 263, page 787-791, (1994).
[29] Duffy, T.S., W.L. Vos, C.S. Zha, H.K. Mao, and R.J. Hemley.  "Sound
     Velocities in Dense Hydrogen and the Interior of Jupiter"  Science 263,
     page 1590-1593, (1994).
[30] Harrington, J., R. P. LeBeau, K. A. Backes, & T. E. Dowling, "Dynamic
     response of Jupiter's atmosphere to the impact of comet P/Shoemaker-
     Levy 9", Nature 368, page 525-527, April 7, 1994.
[31] Olivares, Jose, "Jupiter's Magnificent Show", Astronomy, April 1994,
     page 74-79.
[32] Schmude, Richard W., "Observations of Jupiter During the 1989-90
     Apparition", The Strolling Astronomer: J.A.L.P.O., Vol. 35, No. 3.,
     September 1991.
[33] "Comet heads for collision with Jupiter",Aerospace America,April 1994,
      page 24-29.
[34] "Comet Shoemaker-Levy 9 and Galilean Eclipses", CCD Astronomy, Spring
     1994, page 18-19.
[35] Reston, James Jr., "Collision Course", TIME, May 23, 1994, page 54-61.
[36] "Boom or Bust", Physics Today, June 1994, page 19-21.
[37] Beatty, Kelly and Levy, David H., "Awaiting the Crash - Part II", Sky
     & Telescope, July 1994, page 18-23.
[38] Alan M. MacRobert, "Observing Jupiter at Impact Time", Sky & Telescope,
     July 1994, page 31-35.
[39] Van Horn, Larry, "Countdown to the Crash", Monitoring Times, June 1994,
     page 10-13.
[40] Mallama, Anthony, "Comet Shoemaker-Levy 9 and Galilean Satellite
     Eclipses", CCD Astronomy, Spring 1994, pages 18-19.
[41] B. M. Middlehurst and G. P. Kuiper, "The Moon, Meteorites
     and Comets",  Univ. Chicago Press, 1963.
[42] Boslough, Mark B., et al, "Determination of Mass and Penetration Depth
     of Shoemaker-Levy 9 fragments from time-resolved impact flashed signatures"
     submitted to Geophysical Research Letters, June 1994.
[43] Crawford, David A., et al, "The impact of Comet Shoemaker-Levy 9 on
     Jupiter", submitted to Shock Waves, April 1994.
[44] Bruning, David, "The Comet Crash", Astronomy, June 1994, pages 41-45.

ACKNOWLEDGMENTS

     Thanks to Ross Smith for starting a FAQ and to all those who have
contributed :  Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke,
Rik Hill, Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke,
David H. Levy, Eugene and Carolyn Shoemaker, Jim Scotti, Richard A.
Schumacher, Louis A. D'Amario, John McDonald, Michael Moroney, Byron
Han, Wayne Hayes, David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki,
Jeffrey A. Foust, Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina,
Don Yeomans, Richard Schmude, Lenny Abbey, Chris Lewicki, the Students
for the Exploration and Development of Space (SEDS), David A. Seal,
Leonard Garcia, Raymond Doyle Benge, Mark Boslough, Dave Mehringer,
John Spencer, Erik Max Francis, and John Rogers.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

SL9 LIVE

    The following messages discuss how one could get live updates:

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

Hello, I'm Jim Moskowitz of the Franklin Institute Science Museum.  I was
(tangentially) involved in the 'Neptune All Night' live broadcast we did
over PBS during the '89 Voyager flyby, and I've just learned that we're
going to be doing a PBS broadcast for SL9 as well.
On Wednesday, July 20th, from 10:30 to 11:30 PM EST we'll be providing
PBS stations with a show talking about the impacts and their effects,
featuring images from Hubble, discussion with Levy and the Shoemakers,
a piece by Arthur C. Clarke, and probably much more.
My understanding is that it will be up to the local PBS stations to decide
whether to show this program (as opposed to, maybe, an 'Eastenders' rerun).
You may want to call your area station and express interest in having the
program shown in your area...

-Jim  ([email protected])

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

The Fernbank Science Center in Atlanta, Georgia, USA is planning to have
a video link from their 36-inch telescope down to their planetarium,
so people can view the results of the impact of comet Shoemaker-Levy 9
with Jupiter. Currently, they are working on a press release and hope
to have their plans finalized in June.

For more information call or write:

     Fernbank Science Center
     156 Heaton Park Drive, NE
     Atlanta, Georgia 30307
     USA 404-378-4311

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

     There may be continuous discussion/updates on the IRC (Internet Relay
chat) channel #Astronomy during the impacts.

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\


Clear skies,
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Tue, 14 Jun 1994 03:59:31 +0700
% Message-Id: <[email protected]>
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: [email protected]
% Subject: Comet/Jupiter Collision FAQ
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 14-JUN-1994 12:11:56.85
CC:	
Subj:	Visible fireball caveats

The recent FAQ includes the following paragraph, which requires some
clarification: 

>Simulations by Mark Boslough and others indicate that when the fireball
>resulting from an impact cools it will form a debris cloud that will rise
>hundreds of kilometers above the Jovian cloudtops, and will enter sunlight
>within minutes of the impact.  The arrival time of this giant cloud into
>sunlight would provide data on its trajectory, which in turn would help us
>know how big the comet fragment was.  It is possible that it would be big
>(bright) enough to be seen by amateurs [42,43].  Mark Boslough of Sandia
>National Laboratories also states that the probability is very high that
>these effects will be visible for some of the later impacts (e.g. W and R,
>visible from Hawaii, S, visible from India and the far East, Q1 and Q2,
>visible from Africa, parts of eastern Europe and the Middle East, L, Brazil
>and West Africa, K, South Pacific and Australia, and maybe even V, on the
>final night, visible in the Western half of the U.S.).  Observers in these
>locations are encouraged to anticipate the possibility of seeing the fireball
>within tens of seconds after the impact, and a few minutes later after it has
>cooled, condensed, and entered the sunlight.

This statement assumes that the brightest fragments are 2-4 km in
diameter. If they are less than 1 km (as many astronomers now think)
we don't expect them to be seen.  The point in my statement was to
encourage amateurs to look on the chance that there are indeed
fragments that are greater than 3 km, a possibility that has not been
ruled out.  So the "very high" refers to the probability that a
fireball from a 2-4 km diameter impactor could be seen. Estimates of
the probablility that they are actually that big vary widely. The
apparent visible magnitude of any fireball will be similar to that of
a Galilean satellite at best, but it would appear redder.  They would
be much brighter at infrared wavelengths. 

These issues will be discussed in detail (with all the proper caveats)
in the following article, which we hope will be out soon: 

Boslough, M.B., D.A. Crawford, A.C. Robinson, T.G. Trucano.  Watching
for fireballs on Jupiter, submitted to EOS, 1994. 

We don't want to give people false hope; on the other hand we don't
want anyone to miss out if something is visible.  We estimate the
probability of seeing the fireballs to be about the same as the
probability that the impactors are greater than one kilometer in
diameter. 

Mark Boslough

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Tue, 14 Jun 1994 09:05:57 +0700
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: Mark Boslough <[email protected]>
% Subject: Visible fireball caveats
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 15-JUN-1994 13:05:51.37
CC:	
Subj:	New Predicted Impact Times

[Courtesy of Paul Chodas, JPL]

Attached is our Predicted Impact Parameters table for the week of June 13.

Our latest orbit solutions use astrometric measurements which have
been reduced using a pre-release version of the very accurate
Hipparcos star catalog.  The predicted impact times are generally
earlier than in our table posted June 5, by an average of about 12
minutes.  The impact times for fragments B, F, and P2, however, moved
over 20 minutes earlier, and that for fragment U jumped an hour and
half earlier.  Fragment U's orbit is still very uncertain. 

Paul Chodas
1994 June 14

==============================================================================

  Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
  ---------------------------------------------------------------

  P.W. Chodas, D.K. Yeomans and Z. Sekanina (JPL/Caltech)
  P.D. Nicholson (Cornell)

  Predictions as of 1994 June 12
  Date of last astrometric data in these solutions: 1994 June 8

The predictions for all fragments except Q2 are based on independent orbit
solutions; the orbit reference identifier is now given.  The orbit solution
for fragment Q2 was obtained by applying a disruption model to the orbit
for Q1, and using astrometric measurements of Q2 relative to Q1.

Except for fragment Q2, uncertainties in the impact parameters are given
immediately below the predicted values.  These uncertainties are 1-sigma
values obtained from Monte Carlo analyses; we have made an effort to make
them realistic: they are not formal uncertainty values.  NOTE: To obtain a
95% confidence level, one should use a +/- 2 sigma window around the
predicted values.

The predictions for fragments E, G, H, K, L, Q, R, S, and W are the most
accurate, as these have the best-known orbits; fragments T, U, and V have
the most poorly-determined orbits, (especially U).  The uncertainties for
fragment Q2 have not been quantified, but are probably comparable to those
for fragment P2.

The dynamical model used for these predictions includes perturbations due to
the Sun, planets, Galilean satellites and the oblateness of Jupiter.  The
planetary ephemeris used was DE245.

- ------------------------------------------------------------------------------
Frag-     Impact      Jovicentric  Merid.  Angle          Satellite Longitudes
  ment   Date/Time    Lat.  Long.  Angle   E-J-F  Orbit     at Impact  (deg)
         July (UT)    (deg) (deg)  (deg)   (deg)   Ref.  Amal   Io   Eur   Gany
- --------------h--m------------------------------------------------------------
A = 21   16  19:50   -43.12  173   63.57   99.37   A11   201t  344   106+   76+
                22      .27   13    1.11     .83          11     3     2     1

B = 20   17  02:46   -43.16   65   63.01   99.75   B12    50+   42+  136+   91+
                20      .26   12     .97     .74          10     3     1     1

C = 19   17  06:50   -43.15  212   64.33   98.81   C9    172t   76+  153+   99+
                20      .23   12     .99     .74          10     3     1     1

D = 18   17  11:11   -43.11   10   63.60   99.34   D10   304   113+  171   108+
                23      .28   14    1.16     .87          12     3     2     1

E = 17   17  15:17   -43.56  157   66.02   97.52   E26    67+  148+  188   117+
                14      .09    9     .61     .44           7     2     1     0

F = 16   18  00:16   -43.49  124   63.58   99.25   F17   338o  224   225   136+
                18      .18   11     .85     .63           9     3     1     1

G = 15   18  07:36   -43.68   27   66.65   97.04   G26   198t  287   256   151+
                13      .08    8     .53     .38           7     2     1     0

H = 14   18  19:35   -43.77  102   67.08   96.71   H24   199t   28+  306   176
                13      .08    8     .54     .39           7     2     1     0

K = 12   19  10:26   -43.87  280   67.87   96.12   K25   286   153+    9+e 207
                13      .08    8     .54     .39           7     2     1     0

L = 11   19  22:24   -43.94  353   68.63   95.56   L26   286   255    60+  232
                13      .08    8     .53     .38           7     2     1     0

N = 9    20  10:09   -44.30   60   67.10   96.57   N13   280   355   111+  257
                22      .15   13    1.04     .74          11     3     2     1

P2= 8b   20  14:58   -44.57  236   65.84   97.40   P12    65+   36+  131+  267
                21      .13   12     .96     .68          11     3     1     1

Q2= 7b   20  19:40   -44.39   43   69.10   95.14         206    75+  151+  277

Q1= 7a   20  20:07   -44.09   59   69.52   94.89   Q28   220    79+  153+  278
                12      .07    8     .50     .35           6     2     1     0

R = 6    21  05:47   -44.18   49   69.95   94.56   R23   151   161   193   298
                17      .10   10     .68     .48           9     2     1     1

S = 5    21  15:39   -44.21   46   70.63   94.08   S33    88+  245   234   319
                14      .08    9     .55     .39           7     2     1     0

T = 4    21  18:28   -45.23  152   67.93   95.80   T8    173t  269   246   325
                41      .21   25    1.66    1.16          21     6     3     1

U = 3    21  22:52   -44.69  309   70.30   94.24   U9    306   306   264   334
                68      .28   41    2.46    1.72          34    10     5     2

V = 2    22  03:54   -44.38  133   67.88   95.98   V9     97+  349   285   344
                28      .20   17    1.39     .99          14     4     2     1

W = 1    22  08:21   -44.24  292   70.99   93.80   W26   231    26+  303   354
                17      .10   10     .67     .47           9     2     1     1

Satellite Codes:  +  impact is visible from satellite
                  o  satellite is occulted by Jupiter at impact
                  e  satellite is eclipsed but not occulted at impact
                  t  satellite is in transit across Jupiter
- -----------------------------------------------------------------------------

Notes:
1. Fragments J=13 and M=10 are omitted because they have faded from view.
   Fragments P=8 and Q=7 each consist of multiple components.  The March'94
   HST image shows that P1=8a has almost completely faded away (so it too is
   omitted from the Table), and that P2=8b has split.  We do not as yet
   have sufficient data to obtain independent predictions for the two
   components of P2=8b.

2. The impact date/time is the time the impact would be seen at the Earth
   (if the limb of Jupiter were not in the way); the date is the day in
   July 1994; the time is given as hours and minutes of Universal Time.
   The impact time uncertainty is a 1-sigma value in minutes.

3. The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

4. The impact longitude is System III, measured westwards on the planet. The
   large uncertainty in impact longitudes is due to Jupiter's fast rotation.

5. The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.  This relative
   longitude is known much more accurately than the absolute longitude.
   At the latitude of the impacts, the Earth limb is at meridian angle 76 deg
   and the terminator is at meridian angle 87 deg.

6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact.  All impacts will be just on the
   farside as viewed from Earth; later impacts will be closer to the limb.
   The probability that any fragment will impact on the near side as viewed
   from the Earth is < 0.01%.

7. Satellite data are given for Amalthea, Io, Europa, and Ganymede.  Callisto
   is omitted, as it is too distant to act as a useful reflector of the
   impact flashes, and it has no occultations or eclipses during the impacts.
   Metis, Adrastea and Thebe are also omitted, due to the expected faintness
   of any flash reflections from them.  The satellite longitudes are measured
   east from superior conjunction (the anti-Earth direction).  Longitude
   uncertainties listed as "0" are simply < 0.5 deg.

8. According to these predictions, the only impact certain to occur during a
   satellite eclipse is K=12 with Europa eclipsed.

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% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

Article: 3702
From: [email protected] (Dan Bruton, Texas A&M)
Newsgroups: sci.astro,alt.com,alt.sci.planetary
Subject: Jovian Moon Events for July 1994
Date: 22 Jun 1994 06:02 CDT
Organization: Texas A&M University OpenVMScluster
 
Galilean Satellite Events for July 1994
 
KEY:
 
+---------------------------------------------------------------+
|   SATELLITE                EVENT                 TYPE         |
+---------------------------------------------------------------+
|  I  -> Io               Tr -> Transit         D -> Disappear  |
| II  -> Europa           Sh -> Shadow          R -> Reappear   |
| III -> Ganymede         Ec -> Eclipse         I -> Ingress    |
| IV  -> Callisto         Oc -> Occult          E -> Egress     |
+---------------------------------------------------------------+
 
DESCRIPTION OF TABLE :
 
             Column 1 : Date
             Column 2 : Universal Time
             Column 3 : Satellite (I,II,III,IV)
             Column 4 : Transit, Shadow, Eclipse, or Occult
             Column 5 : Disappear, Reappear, Ingress or Egress
 
 
Jul.  1                                Jul. 16
          1:00 III.Oc.R.                         0:49   I.Sh.I.
          1:50   I.Ec.R.                         1:44   I.Tr.E.
          3:32 III.Ec.D.                         2:57   I.Sh.E.
          5:35 III.Ec.R.                        20:43   I.Oc.D.
         12:58  II.Oc.D.               Jul. 17
         17:37  II.Ec.R.                         0:09   I.Ec.R.
         19:51   I.Tr.I.                        12:12  II.Tr.I.
         20:59   I.Sh.I.                        14:35  II.Tr.E.
         22:00   I.Tr.E.                        14:45  II.Sh.I.
         23:08   I.Sh.E.                        17:07  II.Sh.E.
Jul.  2                                         18:03   I.Tr.I.
         16:57   I.Oc.D.                        19:18   I.Sh.I.
         20:19   I.Ec.R.                        20:12   I.Tr.E.
Jul.  3                                         21:26   I.Sh.E.
          7:09  II.Tr.I.               Jul. 18
          9:31  II.Tr.E.                        15:11   I.Oc.D.
          9:31  II.Sh.I.                        18:38   I.Ec.R.
         11:53  II.Sh.E.                        20:14 III.Tr.I.
         14:19   I.Tr.I.                        22:29 III.Tr.E.
         15:28   I.Sh.I.               Jul. 19
         16:28   I.Tr.E.                         1:27 III.Sh.I.
         17:37   I.Sh.E.                         3:28 III.Sh.E.
Jul.  4                                          7:12  II.Oc.D.
         11:26   I.Oc.D.                         9:35  II.Oc.R.
         12:37 III.Tr.I.                         9:42  II.Ec.D.
         14:47 III.Tr.E.                        12:04  II.Ec.R.
         14:48   I.Ec.R.                        12:32   I.Tr.I.
         17:28 III.Sh.I.                        13:46   I.Sh.I.
         19:29 III.Sh.E.                        14:41   I.Tr.E.
Jul.  5                                         15:55   I.Sh.E.
          2:11  II.Oc.D.               Jul. 20
          6:55  II.Ec.R.                         9:40   I.Oc.D.
          8:47   I.Tr.I.                        13:07   I.Ec.R.
          9:57   I.Sh.I.               Jul. 21
         10:56   I.Tr.E.                         1:29  II.Tr.I.
         12:05   I.Sh.E.                         3:52  II.Tr.E.
Jul.  6                                          4:04  II.Sh.I.
          5:54   I.Oc.D.                         6:25  II.Sh.E.
          9:16   I.Ec.R.                         7:00   I.Tr.I.
         20:24  II.Tr.I.                         8:15   I.Sh.I.
         22:46  II.Tr.E.                         9:09   I.Tr.E.
         22:49  II.Sh.I.                        10:23   I.Sh.E.
Jul.  7                                Jul. 22
          1:11  II.Sh.E.                         4:08   I.Oc.D.
          3:15   I.Tr.I.                         7:36   I.Ec.R.
          4:25   I.Sh.I.                        10:13 III.Oc.D.
          5:24   I.Tr.E.                        12:31 III.Oc.R.
          6:34   I.Sh.E.                        15:29 III.Ec.D.
Jul.  8                                         17:32 III.Ec.R.
          0:22   I.Oc.D.                        20:28  II.Oc.D.
          2:33 III.Oc.D.                        22:52  II.Oc.R.
          3:45   I.Ec.R.                        23:00  II.Ec.D.
          4:47 III.Oc.R.               Jul. 23
          7:31 III.Ec.D.                         1:22  II.Ec.R.
          9:34 III.Ec.R.                         1:28   I.Tr.I.
         15:26  II.Oc.D.                         2:44   I.Sh.I.
         17:48  II.Oc.R.                         3:38   I.Tr.E.
         17:50  II.Ec.D.                         4:52   I.Sh.E.
         20:12  II.Ec.R.                        22:36   I.Oc.D.
         21:43   I.Tr.I.               Jul. 24
         22:54   I.Sh.I.                         2:04   I.Ec.R.
         23:52   I.Tr.E.                        14:47  II.Tr.I.
Jul.  9                                         17:10  II.Tr.E.
          1:03   I.Sh.E.                        17:23  II.Sh.I.
         18:50   I.Oc.D.                        19:44  II.Sh.E.
         22:14   I.Ec.R.                        19:57   I.Tr.I.
Jul. 10                                         21:12   I.Sh.I.
          9:40  II.Tr.I.                        22:06   I.Tr.E.
         12:02  II.Tr.E.                        23:21   I.Sh.E.
         12:08  II.Sh.I.               Jul. 25
         14:30  II.Sh.E.                        17:05   I.Oc.D.
         16:11   I.Tr.I.                        20:33   I.Ec.R.
         17:23   I.Sh.I.               Jul. 26
         18:20   I.Tr.E.                         0:09 III.Tr.I.
         19:31   I.Sh.E.                         2:25 III.Tr.E.
Jul. 11                                          5:26 III.Sh.I.
         13:18   I.Oc.D.                         7:26 III.Sh.E.
         16:23 III.Tr.I.                         9:45  II.Oc.D.
         16:43   I.Ec.R.                        12:09  II.Oc.R.
         18:36 III.Tr.E.                        12:17  II.Ec.D.
         21:27 III.Sh.I.                        14:26   I.Tr.I.
         23:28 III.Sh.E.                        14:39  II.Ec.R.
Jul. 12                                         15:41   I.Sh.I.
          4:41  II.Oc.D.                        16:35   I.Tr.E.
          7:04  II.Oc.R.                        17:49   I.Sh.E.
          7:08  II.Ec.D.               Jul. 27
          9:30  II.Ec.R.                        11:34   I.Oc.D.
         10:39   I.Tr.I.                        15:02   I.Ec.R.
         11:51   I.Sh.I.               Jul. 28
         12:48   I.Tr.E.                         4:05  II.Tr.I.
         14:00   I.Sh.E.                         6:29  II.Tr.E.
Jul. 13                                          6:41  II.Sh.I.
          7:46   I.Oc.D.                         8:54   I.Tr.I.
         11:12   I.Ec.R.                         9:03  II.Sh.E.
         22:55  II.Tr.I.                        10:10   I.Sh.I.
Jul. 14                                         11:03   I.Tr.E.
          1:18  II.Tr.E.                        12:18   I.Sh.E.
          1:26  II.Sh.I.               Jul. 29
          3:48  II.Sh.E.                         6:03   I.Oc.D.
          5:07   I.Tr.I.                         9:31   I.Ec.R.
          6:20   I.Sh.I.                        14:10 III.Oc.D.
          7:16   I.Tr.E.                        16:29 III.Oc.R.
          8:29   I.Sh.E.                        19:28 III.Ec.D.
Jul. 15                                         21:31 III.Ec.R.
          2:14   I.Oc.D.                        23:02  II.Oc.D.
          5:40   I.Ec.R.               Jul. 30
          6:21 III.Oc.D.                         1:26  II.Oc.R.
          8:37 III.Oc.R.                         1:35  II.Ec.D.
         11:30 III.Ec.D.                         3:23   I.Tr.I.
         13:33 III.Ec.R.                         3:57  II.Ec.R.
         17:56  II.Oc.D.                         4:38   I.Sh.I.
         20:19  II.Oc.R.                         5:32   I.Tr.E.
         20:25  II.Ec.D.                         6:47   I.Sh.E.
         22:47  II.Ec.R.               Jul. 31
         23:35   I.Tr.I.                         0:32   I.Oc.D.
                                                 4:00   I.Ec.R.
                                                17:24  II.Tr.I.
                                                19:48  II.Tr.E.
                                                20:00  II.Sh.I.
                                                21:52   I.Tr.I.
                                                22:22  II.Sh.E.
                                                23:07   I.Sh.I.
 
-----
 
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .
 

From:	US4RMC::"[email protected]" "Ron Baalke" 22-JUN-1994 
To:	[email protected]
CC:	
Subj:	Caltech Scientists Eagerly Await Comet/Jupiter Collision

For Immediate Release	June 17, 1994
The Comet Collision:  Caltech Scientists Eagerly Await Celestial Event

The impending crash of the twenty-odd fragments of comet Shoemaker-Levy 9
into Jupiter from July 16 through 22 promises to be one of the most-watched
celestial events ever, and planetary scientists and astronomers around the
globe are eagerly anticipating the results.  At Caltech some scientists are
doing more than just anticipating, they are creating detailed models that
predict in considerable detail how the Jovian calamity will play out, and are
helping plan observations to catch the event at its peak.  Following are the
Caltech scientists who are most involved, and a description of their work.

Thomas Ahrens, Professor of Geophysics
John O'Keefe, Visiting Associate in Planetary Science

Ahrens and his collaborators, graduate student Toshiko Takata, O'Keefe, and
the Jet Propulsion Laboratory's Glenn Orton, have created a detailed computer
model of what may happen as the shards of Shoemaker-Levy 9 plunge into
Jupiter.  The icy chunks, streaking towards the planet at 60 kilometers per
hour, may create bright flashes as each of them first hits the atmosphere,
just as meteors do on Earth, and then disintegrates as the thickening
atmosphere slows it down.  The calculations predict that, after comet
fragments between 0.4 and 10 kilometers in diameter have pierced the clouds
to depths of several hundred kilometers, the tremendous kinetic energy of the
pieces will have compressed and heated Jupiter's gaseous hydrogen clouds to
nearly the temperature of the surface of the sun.  This superheated gas will
then expand rapidly and form a plume on the surface, much like the mushroom
cloud from a hydrogen bomb detonated on Earth, that may be visible from Earth
over the limb, or edge, of Jupiter.  This gas plume is predicted to increase
the brightness of Jupiter by approximately a factor of two.

Andrew Ingersoll, Professor of Planetary Science

Ingersoll is a member of a team which will be looking for evidence of waves
caused by the impacts in Jupiter's atmosphere.  Using the Hubble Space
Telescope at visible and near-infrared wavelengths, the team hopes to detect
subtle changes in the surface clouds, especially changes creating a circular
pattern around the impact point, like ripples in a pond.  As a wave passes
through a point in the atmosphere, the local pressure will rise and then
fall, causing the temperature to cool and then warm very slightly, by about
one degree Fahrenheit.  In areas where gas is just on the edge of freezing,
the passing wave's small pressure change should be enough to cause ice
crystals to form.  Ammonia droplets are the most likely to freeze out, which
would create new cloud patterns of white crystals.

Ingersoll has also worked with Hiroo Kanamori, the Smits Professor of
Geophysics and director of Caltech's seismological laboratory, and Tim
Dowling at MIT, to model what kinds of waves may jostle Jupiter as a result
of this impact.  One intriguing idea is that the biggest waves will be
confined to a narrow altitude range, where the pressure is about 3 to 5 bars,
and where there is a layer of gaseous water encircling the planet.  (For
comparison, the sea-level air pressure on Earth is about 1 bar, and the
pressure at Jupiter's cloud tops is about 0.5 bar.)  The temperature and
density of this layer should have just the right properties so that if the
wave travels too high, it will be refracted, or bent, downward.  And if the
wave travels too low, it will be refracted upward.  The net effect is to
create an internal wave channel, which should allow the waves to spread a
very long distance horizontally.  These long-distance waves would act as a
probe of Jupiter's interior, much like seismic waves on Earth, and would
provide information about different atmospheric levels that cannot be
observed optically.  Ingersoll and his colleagues hope to detect the water
cloud by these observations.

Gerry Neugebauer, Howard Hughes Professor and Professor of Physics
Keith Matthews, Member of the Professional Staff, Division of Physics,
Mathematics, and Astronomy

Neugebauer and Matthews are part of a team, led by Phil Nicholson from
Cornell University, which will be observing Jupiter in the near- to
mid-infrared wavelength (1-20 microns) with the 5-meter Hale Telescope atop
Palomar Mountain, near San Diego.  They will be looking for evidence of
impact flashes, some of which may be bright enough to cause noticeable
reflections from the faint rings around Jupiter, or from the halos of gas and
dust around the trailing comet fragments.  It's possible the plume of
superheated gas may be visible over the limb, or edge, of the planet, and
that this plume may also reflect the flash.

The team will also be looking for the faint temperature changes expected to
result from the outwardly spreading waves in the atmosphere, which would be
directly visible in the infrared.  And they will be making spectroscopic
observations to check for chemical changes.  That is, they will study the
light from Jupiter by breaking it into a spectrum, or rainbow, in order to
examine the bright and dark lines characteristic of different molecules.  The
impact should create considerable vertical mixing, dredging up from deep in
the planet chemicals that are rare on the surface, and bringing them into
view.

Duane Muhleman, Professor of Planetary Science

Muhleman will be working at Caltech's Owens Valley Radio Observatory (OVRO)
with research fellow Tony Phillips and graduate student Mark Gurwell.  The
trio will be observing near the 3-millimeter wavelength, looking for
aftereffects of the impact.  This radio wavelength allows them to see what's
happening dozens of kilometers below the tops of the visible clouds, at a
level where disturbances caused by the comet are likely to be noticeable. 
Based on their observations, Muhleman hopes to make a good estimate of the
size of the disturbance and of how much energy went into creating it.

Jonas Zmuidzinas, Assistant Professor of Physics
Geoffrey Blake, Associate Professor of Cosmochemistry

Zmuidzinas and Blake are collaborating with principal investigator Peter
Wannier of the Jet Propulsion Laboratory on Southern Hemisphere observations
to be conducted aboard NASA's Kuiper Airborne Observatory, a plane that flies
in the upper reaches of our own atmosphere.  Zmuidzinas has built an
instrument called a spectrometer which can detect radiation characteristic of
various molecules, including water vapor.  To avoid interference from water
molecules in the air, the instrument will be carried above most of the
atmosphere on the Kuiper Observatory.  And to have a better, Southern
Hemisphere view of the action, the plane will fly out of Melbourne,
Australia.  Water on Jupiter is usually buried beneath the upper cloud
layers, but the comet may mix the upper and lower layers of the atmosphere
enough to churn detectable amounts of water vapor to the surface.  The
spectrometer should be able to determine both the height and the temperature
of plumes that contain water vapor, plumes that are expected to result from
the collisions.

Contact: Jay Aller          or	  Max Benavidez
         (818) 395-3631	          (818) 395-3226
         [email protected]        [email protected]

                               #####
      ___    _____     ___
     /_ /|  /____/ \  /_ /|     Ron Baalke     | [email protected]
     | | | |  __ \ /| | | |     JPL/Telos      | 
  ___| | | | |__) |/  | | |__   Galileo S-Band | If you follow the herd, you
 /___| | | |  ___/    | |/__ /| Pasadena, CA   | will eventually end up in the
 |_____|/  |_|/       |_____|/                 | slaughter house.

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 23-JUN-1994 
CC:	
Subj:	New SL9 Files, Refraction, etc.

To : SL9 Mailing List

Here are some more files in /pub/comet or /incoming at tamsun.tamu.edu.
See Q2.10 of our FAQ list to find out how to get these files by email.

jul1994.moons - Galilean Satellite events for July 1994; Eclipses,
                shadows, etc. 

impacts-12jun.gif -  plot showing the fragment impact times from Chodas
                     et al.'s solution of June 12 1994, overplotted on the
                     times of occultation and eclipse of the major Jovian
                     satellites. Event K=12 remains the only certain impact
                     to occur during an eclipse (of Europa).

wasserman5.gif  - Jupiter-Facing Hemispheres of Earth at Impact Times
                  of SL-9; L. Wasserman, Version 5

The following files are now in /pub/comet/sandia:

sandia-eosfig3.ps - Limb and sunlight arrival times for debris (fireball)
                    from SL-9 fragments (1 km & 3 km fragments)

sandia-eosfig3.gif - GIF version of sandia-eosfig3.ps

Someone wrote:

<> Just one question, what if this comet had collided with Earth?

 Here's a quote:

    "...we're talking about a million megatons of kinetic energy.  We're
     talking about the kind of event that is associated with mass extinction
     of species on Earth.  Really and truly a global catastrophe.  It might
     not take out the human race but it would certainly be very bad times."

                                                -- Eugene Shoemaker on CNN

<> The refraction of sunlight near dusk makes the sun set a few
<> minutes later than the simple geometry would indicate; the
<> variable density of the atmosphere makes the sun's image
<> visible to people a few degrees into the night side of Earth.
<> A corresponding effect will operate on Jupiter, directing some
<> impact light around the disk from the night side toward us.

I used Roger W. Sinnott's program for atmospheric refraction (S&T March 1989
page 312) and used the following parameters:

T0 = -166     :   ' Atmospheric Temperature (F) at the cloudtops
N0 = 1.00015  :   ' Refr Index at the cloudtops
R0 = 11.194   :   ' Planet Radius in units of Earth Radius
M = 317.89    :   ' Planet Mass in units of Earth Mass
W = 2.016     :   ' Average Mol. Weight of the Atmosphere

Result : To an observer at Jupiter's cloudtops, the center of the
sun's disk will appear on the horizon when the center of the
sun is actually 0.55 degrees below the horizon (refraction effects only).
If this is correct, then perhaps refraction could help a little.
The refraction of the light from a fireball has a different geometry
than this sunset example so I will try to work on the problem.

<> I have never seen listed or published current magnitude
<> estimates for SL9 (only its discovery magnitude of 13.8
<> or so).  Are the fragments within reach of an amateur CCD camera?

The brightest fragments currently have visual magnitudes of about 20 I think.

----

Here are some approximate coordinates of some spots on Jupiter
that we are tracking.  Does anyone have more accurate coordinates
or names for these?  All the spots here are white except for the
first one.

   Spot    Latitude  System II Longitude     Approx. Size       Location
-----------------------------------------------------------------------------
    GRS     -20             41             29000 by 12000 km
     BC     -30            160              7500 by 4000 km       STB
     DE     -30            175              7500 by 4000 km       STB
     FA     -30            240              7500 by 4000 km       STB
     ?      -30            195                  5000 km           STB
     ?      -21            299                  7000 km           STrZ
     ?      -35            248                  3000 km           STZ
     ?      -35            148                  3000 km           STZ
     ?      -35            153                  3000 km           STZ

Clear skies,
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .


% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Thu, 23 Jun 1994 05:52:47 +0700
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% Originator: [email protected]
% Sender: [email protected]
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% Subject: New SL9 Files, Refraction, etc.
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 23-JUN-1994 11:10:48.90
CC:	
Subj:	Comet Celebration

Please distribute widely:

*******************************************************

                   U.C. Berkeley's 
  NASA Extreme Ultraviolet Explorer satellite project 

                         and 

                 the Exploratorium 

                       present 

        -------------------------------------
         C O S M I C   C O L L I S I O N S : 

        A Celebration of the Impending Impact 
         of Comet Shoemaker-Levy 9 on Jupiter
        -------------------------------------

                Thursday, July 14, 1994
                  6:30 pm - 10:00 pm
              Palace of Fine Arts Theater
                    San Francisco

*******************************************************

                 Join guest speakers:

*Dr. Marcia Neugebauer 
  Comet Specialist, NASA's Jet Propulsion Laboratory

*Dr. Jere Lipps
  Director, University of California Museum of Paleontology 

*Dr. Randy Gladstone
  Planetary Scientist, Extreme Ultraviolet Explorer Guest Observer

*Kevin Anderson 
  Science Fiction Writer, 
   author of the current New York Times Best Seller 
   "STAR WARS; Dark Apprentice, Volume 2 of the Jedi Academy Trilogy" 

*Poul Anderson
  Science Fiction Writer, 
   author of "Harvest of Stars" and winner of seven Hugo and 
   three Nebula Awards.

--------------------------------------------------------------

The evening will highlight the upcoming comet impact, other comet
collisions in the past, including the comet theory of dinosaur mass
extinction, plus the role of cosmic collisions in popular culture. 

EXHIBITS AND BOOTHS - doors open at 6:30 p.m. 
Tentatively Scheduled Participants to include:

  * Center for Extreme Ultraviolet Astrophysics
  * Exploratorium
  * Another Change of Hobbit
  * Bay Area Musician's Forum 
  * Hearts of Space Records
  * Leonardo/International Society of Arts, Sciences, and Technology
  * Mondo 2000 magazine
  * The Nature Company
  * Wired magazine
  * YLEM: Artists Using Science and Technology

TALKS begin promptly at 7:30 p.m.

*********************************************
Both Kevin Anderson and Poul Anderson will be
available for BOOK SIGNINGS.
*********************************************

General Admission ........... $10.00
Exploratorium Members ....... $ 8.00

Thursday, July 14, 1994, 6:30 pm - 10:00 pm,
Palace of Fine Arts, San Francisco

For tickets and further information, please contact 
CITY BOX OFFICE - (415) 392-4400

*******************
TICKETS NOW ON SALE 
*******************

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Thu, 23 Jun 1994 08:06:43 +0700
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: [email protected]
% Subject: Comet Celebration
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List
% X-Mailer: America Online Mailer

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 27-JUN-1994 
CC:	
Subj:	NASA TV Coverage of Comet Shoemaker-Levy

Donald Savage
Headquarters, Washington, D.C.                                           

June 27, 1994
(Phone:  202/358-1547)
 
Michael Finneran
Goddard Space Flight Center, Greenbelt, Md.
(Phone:  301/286-5565)
 
Lynn Simarski
National Science Foundation, Arlington, Va.
(Phone:  703/306-1070)
 
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
(Phone:  410/338-4514)
 
NOTE TO EDITORS:  N94-46
 
NEWSROOM HOURS AND TV COVERAGE FOR COMET SHOEMAKER-LEVY 9
 
        NASA's coverage of the impact of Comet P/Shoemaker-Levy 
9 during the week of July 16-22 includes a series of live, 
televised press briefings and a 24-hour newsroom operation at 
the Goddard Space Flight Center (GSFC), Greenbelt, Md.
 
        The Goddard Comet Impact newsroom will be the central 
location providing coverage of observations and images from 
the worldwide network of ground-based observatories and 
spacecraft taking part in the NASA/National Science Foundation 
observing project.  Scientists will be on hand at the newsroom 
to answer questions, or interviews can be arranged as needed.  
Press materials, artwork and video relating to the event will 
be available to media.  
 
        The first fragment of the comet will impact Jupiter just 
before 4 p.m. EDT on the side of Jupiter facing away from 
Earth.  Shortly afterwards, the point of impact will rotate 
into view as seen from Earth.  The first image of the impact 
area is expected to be available (following minimal 
processing) at about 10 p.m. EDT.
 
        NASA will release the image in a live program broadcast 
from the Space Telescope Science Institute, Baltimore, Md., 
starting at 10 p.m. EDT.  There will be no press briefing on 
NASA TV at that time, however, a briefing will be held Sunday 
morning at the Goddard Comet Impact Newsroom.
 
Press Briefing Schedule
 
        At 8:00 a.m. EDT, Sunday, July 17, a press briefing will 
be broadcast live on NASA TV with Q & A from other NASA 
Centers, and will include updated information about the first 
impact and the image.  During the following week, NASA will 
hold a live press briefing each day at the GSFC Comet Impact 
Newsroom (see schedule below).
 
        The briefing panels will include Comet co-discoverers 
Drs. Eugene and Carolyn Shoemaker and David Levy on most days 
as well as scientists presenting images and information from 
the Hubble Space Telescope and other spacecraft.  Dr. Lucy 
McFadden will have a round-up of observations from ground-
based observatories around the world.  The program and 
briefing schedule follows:
 
JULY DATE       TIME (EDT)      EVENT
Sat.    16      10:00 p.m.      Live from HST: First  Impact Image Release
                                (no Q & A from NASA Centers)
Sun.    17      8:00 a.m.       Press Briefing at GSFC
Mon.    18      8:00 a.m.       Press Briefing at GSFC
Tue.    19      8:00 a.m.       Press Briefing at GSFC
Wed.    20      12:00 noon      Press Briefing at GSFC
Th.     21      8:00 a.m.       Press Briefing at GSFC
Fri.    22      9:30 a.m.       Press Briefing at GSFC
Sat.    23      8:00 a.m.       Press Briefing at GSFC
 
Note:  The above times are dependent on the STS-65 mission 
schedule.  If there is a change in the launch or landing time 
of the Shuttle, the program times will change.  
 
Comet Impact Newsroom Operations
 
        The newsroom will operate on a 24-hour basis beginning 
at 6 a.m., Sun., July 17 until noon EDT, July 23.  The 
newsroom will be located at the Goddard Visitor's Center on 
Soil Conservation Road in Greenbelt.  The phone number for the 
newsroom will be 301/286-2300, but will not be active until 6 
a.m., July 17.  
 
        Media wishing to use the newsroom must register at the 
Visitor Center and obtain a media badge, starting at 6 a.m. 
EDT July 17.  Valid press credentials and a photo ID must be 
presented.  Media representatives who are not U.S. citizens 
must contact the Goddard Office of Public Affairs at 301/286-
8955 before registering.
 
Video Uplink Schedule
 
        NASA will provide feeds of b-roll and animation of the 
comet impacts with Jupiter on the following schedule:  
 
June 29:        10:00 a.m. and 1:30 p.m. EDT
June 30:        10:30 a.m. and 1:30 p.m. EDT
July 5:         10:30 a.m. and 1:30 p.m. EDT
July 15:        1:00 p.m. EDT
 
        Also on July 5, NASA Television will replay the May 18 
press briefing with panelists Dr. Eugene Shoemaker, Dr. Heidi 
Hammell, Dr. Hal Weaver, Dr. Lucy McFadden, and Dr. Melissa McGrath.
 
        NASA TV is carried on Spacenet 2, transponder 5, channel 9, 69
degrees West, transponder frequency is 3880 MHz, audio subcarrier is
6.8 MHz, polarization is horizontal. 

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Mon, 27 Jun 1994 12:17:14 +0700
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% Errors-To: [email protected]
% Reply-To: [email protected]
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% Subject: NASA TV Coverage of Comet Shoemaker-Levy
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 27-JUN-1994 19:31:34.16
CC:	
Subj:	New SL9 impact time predictions

[Courtesy of Paul Chodas, JPL]

---------------

Attached is the June 24 edition of our Predicted Impact Parameters table.

The predicted impact times continue to slide earlier, but generally only
about 5 minutes earlier than those in our table of June 14.  However, the
impact times for A, B, R, and S made larger jumps (15 to 20 minutes earlier),
and the times for T and U moved the most (half an hour and a full hour
earlier, respectively).  Fragment U's orbit is finally becoming reasonably
well-determined, the last one to fall into line.

Paul Chodas
1994 June 24

==============================================================================

  Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
  ---------------------------------------------------------------

  P.W. Chodas, D.K. Yeomans and Z. Sekanina (JPL/Caltech)
  P.D. Nicholson (Cornell)

  Predictions as of 1994 June 24
  Date of last astrometric data in these solutions: 1994 June 16

The predictions for all fragments except Q2 are based on independent orbit
solutions; our orbit reference identifier is now given.  The orbit solution
for fragment Q2 was obtained by applying a disruption model to the orbit
for Q1, and using astrometric measurements of Q2 relative to Q1.

Except for fragment Q2, uncertainties in the impact parameters are given
immediately below the predicted values.  These uncertainties are 1-sigma
values obtained from Monte Carlo analyses; we have made an effort to make
them realistic: they are not formal uncertainty values.  NOTE: To obtain a
95% confidence level, one should use a +/- 2 sigma window around the
predicted values.  The uncertainties for Q2 have not been quantified, but
are probably comparable to those for fragment P2.

The dynamical model used for these predictions includes perturbations due to
the Sun, planets, Galilean satellites and the oblateness of Jupiter.  The
planetary ephemeris used was DE245.

 ------------------------------------------------------------------------------
Frag-     Impact      Jovicentric  Merid.  Angle          Satellite Longitudes
  ment   Date/Time    Lat.  Long.  Angle   E-J-F  Orbit     at Impact  (deg)
         July (UT)    (deg) (deg)  (deg)   (deg)   Ref.  Amal   Io   Eur   Gany
 -------------h--m-------------------------------------------------------------
A = 21   16  19:30   -42.87  162   62.87   99.92   A14   191t  341   105+   76+
                20      .27   12    1.07     .81          10     3     1     1

B = 20   17  02:34   -42.95   59   62.68  100.03   B15    45+   40+  135+   90+
                17      .25   10     .94     .71           9     2     1     1

C = 19   17  06:49   -43.09  211   64.42   98.76   C11   172t   76+  153+   99+
                17      .21   10     .93     .70           9     2     1     1

D = 18   17  11:13   -43.11   11   63.91   99.12   D12   305   113+  171   108+
                20      .25   12    1.09     .82          10     3     1     1

E = 17   17  15:10   -43.42  152   66.09   97.50   E28    64+  146+  188   117+
                13      .08    8     .58     .42           7     2     1     0

F = 16   18  00:12   -43.41  122   63.72   99.17   F19   336   224   225   136+
                15      .16    9     .79     .58           8     2     1     1

G = 15   18  07:30   -43.59   24   66.62   97.08   G28   195t  286   255   151+
                11      .07    7     .51     .37           6     2     1     0

H = 14   18  19:26   -43.68   96   66.96   96.81   H26   194t   27+  305   176
                12      .07    7     .52     .37           6     2     1     0

K = 12   19  10:21   -43.79  276   67.85   96.15   K27   284   153+    8+e 207
                11      .07    7     .50     .36           6     2     1     0

L = 11   19  22:18   -43.84  349   68.66   95.55   L28   283   254    60+  232
                12      .07    7     .52     .37           6     2     1     0

N = 9    20  10:08   -44.13   59   67.27   96.48   N16   279   355o  111+  257
                20      .14   12    1.01     .72          10     3     1     1

P2= 8b   20  14:52   -44.45  233   65.81   97.44   P14    62+   35+  131+  267
                17      .12   10     .88     .62           9     2     1     1

Q2= 7b   20  19:37   -44.49   50   69.37   94.93         204    75+  151+  277

Q1= 7a   20  20:04   -43.99   57   69.54   94.89   Q30   218    78+  153+  278
                11      .07    7     .50     .35           6     2     1     0

R = 6    21  05:31   -44.02   40   69.74   94.74   R26   143   158   192   298
                14      .09    8     .62     .43           7     2     1     0

S = 5    21  15:18   -44.12   35   70.15   94.43   S35    78+  242   232   318
                13      .08    8     .53     .37           7     2     1     0

T = 4    21  18:01   -45.01  136   66.97   96.51   T10   159t  265   244   324
                28      .18   17    1.30     .92          14     4     2     1

U = 3    21  21:52   -44.33  274   69.09   95.14   U12   275   298   260   332
                40      .22   24    1.75    1.23          20     6     3     1

V = 2    22  03:44   -44.25  128   67.70   96.14   V11    92+  348   284   344
                25      .19   15    1.32     .94          13     4     2     1

W = 1    22  08:12   -44.20  287   70.79   93.96   W28   226    25+  303   353
                15      .10    9     .64     .44           8     2     1     1

Satellite Codes:  +  impact is visible from satellite
                  o  satellite is occulted by Jupiter at impact
                  e  satellite is eclipsed but not occulted at impact
                  t  satellite is in transit across Jupiter
-------------------------------------------------------------------------------

Notes:

1. Fragments J=13, M=10, and P1=8a are omitted because they have faded from
   view.  The March '94 HST images show that P2=8b and G=15 have split; we do
   not as yet have sufficient data to obtain independent predictions for the
   sub-components.

2. The impact date/time is the time the impact would be seen at the Earth
   (if the limb of Jupiter were not in the way); the date is the day in
   July 1994; the time is given as hours and minutes of Universal Time.
   The impact time uncertainty is a 1-sigma value in minutes.

3. The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

4. The impact longitude is System III, measured westwards on the planet. The
   large uncertainty in impact longitudes is due to Jupiter's fast rotation.

5. The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.  This relative
   longitude is known much more accurately than the absolute longitude.
   At the latitude of the impacts, the Earth limb is at meridian angle 76 deg
   and the terminator is at meridian angle 87 deg.

6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact.  All impacts will be just on the
   farside as viewed from Earth; later impacts will be closer to the limb.

7. Satellite longitudes are given for Amalthea, Io, Europa, and Ganymede.
   The longitudes are measured east from superior conjunction (the anti-Earth
   direction).  Longitude uncertainties listed as "0" are simply < 0.5 deg.

8. According to these predictions, the only impact certain to occur during a
   satellite eclipse is K=12 with Europa eclipsed.

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Mon, 27 Jun 1994 16:18:12 +0700
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% Errors-To: [email protected]
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% Subject: New SL9 impact time predictions
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 27-JUN-1994 20:42:13.59
CC:	
Subj:	SL9 "best locations" table

[Courtesy of Paul Chodas, JPL]

-----------------

Predicted Impact Times for Fragments of Shoemaker-Levy 9
- --------------------------------------------------------

   P.W. Chodas and D.K. Yeomans / JPL

   Predictions as of 1994 June 25


- -----------------------------------------------------------
Fragment    Impact Time        Best Locations for Viewing
               (PDT)             Jupiter at Impact Time
- -----------------------------------------------------------
   A     July 16 12:30 p.m.    Africa (except W. Africa),
                                Middle East, Eastern Europe
   B              7:34 p.m.    Eastern N. America, Mexico,
                                Western S. America
   C             11:49 p.m.    New Zealand, Hawaii

   D     July 17  4:13 a.m.    Australia, New Zealand,
                                Japan
   E              8:10 a.m.    India, Southern China,
                                S.E. Asia, Western Australia
   F              5:12 p.m.    S. America

   G     July 18 12:30 a.m.    New Zealand, Hawaii

   H             12:26 p.m.    Africa (except W. Africa),
                                Middle East, Eastern Europe
   K     July 19  3:21 a.m.    Australia, New Zealand

   L              3:18 p.m.    Brazil, W. Africa, Spain

   N     July 20  3:08 a.m.    Australia, New Zealand

   P2             7:52 a.m.    India, Southern China,
                                S.E. Asia, Western Australia
   Q1             1:04 p.m.    Africa (except W. Africa),
   Q2            12:37 p.m.     Middle East, Eastern Europe
   R             10:31 p.m.    Hawaii, West coast N. America

   S     July 21  8:18 a.m.    India, Southern China,
                                S.E. Asia, Western Australia
   T             11:01 a.m.    Africa (except W. Africa),
                                Middle East, Eastern Europe
   U              2:52 p.m.    Brazil, W. Africa, Spain

   V              8:44 p.m.    Western U.S., Mexico

   W     July 22  1:12 a.m.    New Zealand, Hawaii,
                                Eastern Australia

Note:  These predictions are accurate to plus or minus half an hour.

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Mon, 27 Jun 1994 17:27:55 +0700
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% Errors-To: [email protected]
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From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 29-JUN-1994 
CC:	
Subj:	New comet SL9 / Jupiter impact WWW page

The Center for Extreme Ultraviolet Astrophysics, science operations
center of the EUVE (Extreme Ultraviolet Explorer) Satellite is proud
to announce its Comet Shoemaker Levy 9 /Jupiter impact page. Featuring
San Francisco Bay area Comet SL9 / Jupiter events, New Pictures, New
Movies, Satellite & Ground observatory information, FTP site locations, 
WWW links, Mailing lists & more. 

http://cea-ftp.cea.berkeley.edu/Jupiter/

==========================================================================
Center for Extreme Ultraviolet Astrophysics
University of California Berkeley

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% Date: Tue, 28 Jun 1994 21:40:50 +0700
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% Errors-To: [email protected]
% Reply-To: [email protected]
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% Sender: [email protected]
% From: Dave Meriwether <[email protected]>
% Subject: New comet SL9 / Jupiter impact WWW page
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 30-JUN-1994 
CC:	
Subj:	Planetary Spacecraft Observations of Comet Shoemaker-Levy

JPL FACT SHEET
June 1994

           COMET SHOEMAKER-LEVY 9 IMPACT WITH JUPITER:
                PLANETARY SPACECRAFT AS OBSERVERS

     Three NASA spacecraft missions launched some years ago to
explore various planets and the sun will observe the events
surrounding the Shoemaker-Levy 9 impacts with Jupiter from unique
perspectives far removed from Earth.  They are Voyager 2, Galileo
and the joint NASA/European Space Agency Ulysses mission.

     Voyager and Galileo will be the only two spacecraft actually
in view of the nightside impact points for the many comet fragments.  

     Voyager 2, launched in August 1977 and now leaving the solar
system after flying by and observing Jupiter, Saturn, Uranus and
Neptune, will be some 6 billion kilometers (3.7 billion miles)
from Jupiter in mid-July when the events begin.  It will use its
ultraviolet spectrometer and its planetary radio astronomy
instrument to detect and measure emissions stimulated by the
comet impacts. 

     The Galileo spacecraft is now on the final leg of its flight
path to Jupiter after a complex interplanetary trajectory
involving gravity-assist flybys of Venus and Earth and two
encounters with asteroids. It is scheduled to send a probe into
Jupiter's atmosphere and begin a two-year Jupiter orbital tour in
December 1995.

     Galileo will be about 240 million kilometers (150 million
miles) from Jupiter between July 16 and July 22, 1994, when the
comet fragments are colliding with the planet, and will view the
nightside impact regions directly.  At that range, its camera can
resolve Jupiter as a disc 60 pixels across, comparable to the
capability of many large Earth-based telescopes.  (A pixel, or
picture element, is one point in the digitized picture.)

     Galileo's near-infrared mapping spectrometer, the
photopolarimeter and the ultraviolet spectrometer will measure
all of the light from Jupiter, attempting to detect increases at
the time of the impacts.  Plasma-wave sensors and the dust
detector will be operating to detect radio emissions from the
impacts and to search for changes in Jupiter's dust environment.

     The Galileo imaging team plans to try several different
strategies to capture the Shoemaker-Levy phenomena.  One approach
is to collect many time-lapse exposures in mosaic patterns,
because the times of impact will be uncertain to within many
minutes.  The timing uncertainties and data storage limitations
mean that this procedure can be used to observe only a few of the
fragment collisions.  Multi-color imaging -- in which the camera
takes several exposures in a row through various colored filters
-- will be attempted for other impacts.

     The commands to execute this complex, multiple-instrument
observation program must be transmitted to the spacecraft many
days in advance, with limited opportunity for later updates.  The
spacecraft will then carry out the program when the time comes, while 
the flight team monitors its actions and receives some science data 
sent back at a low rate over Galileo's low-gain antenna.

     After the Shoemaker-Levy events have concluded, the flight
team will search through data recorded on Galileo's onboard tape
recorder and will command the spacecraft to selectively transmit
observations of interest.  This selective procedure has been
proven in the two asteroid encounters.  It may be as late as
October or November 1994 before the majority of Galileo's data
from these events are transmitted to Earth from the spacecraft.

     Ulysses, the NASA/ESA mission to study the poles of the Sun,
will also search for possible radio emissions caused by
Shoemaker-Levy.  During July the spacecraft will be in the midst
of its southern passage around the Sun -- measuring the solar
wind as well as fields and particles from positions less than 20
degrees from the Sun's south pole.

     At that time Ulysses will be about 400 million kilometers
(250 million miles) from the sun, and about twice that distance
from Jupiter.  Its combined radio and plasma wave instrument will
also search for radio emissions from Jupiter's magnetosphere that
show effects of the Shoemaker-Levy impacts. 

                              #####

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Thu, 30 Jun 1994 12:40:49 +0700
% Reply-To: [email protected]
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From:	US4RMC::"[email protected]" "MAIL-11 Daemon"  2-JUL-1994 
CC:	
Subj:	JPL Open House/Comet Shoemaker-Levy Activities

JPL Open House Observing Plans for Comet Shoemaker-Levy

Comet Shoemaker-Levy Display with Link to Mt. Wilson

There will be a Comet Shoemaker-Levy display set up for the JPL Open
House on July 16 & 17. The display will be in the museum area next to
Von Karman Auditorium and will be staffed by Gil Clark. A one-page
handout will be available. There will also be a link to Mt. Wilson
Observatory, and Gil Clark will be downloading images from Mt. Wilson
and displaying them during the Open House. 

JPL Astronomy Club

Comet Fragment B impact will be occuring on July 16, the same day as
the JPL Open House>. The impact is scheduled to occur at 7:34 PM PDT.
Members of the JPL Astronomy Club will be setting up telescopes in the
West parking lot at 5PM when the Open House closes, and plan to stay
until 10PM to view the Fragment B event. 

General Information on the JPL Open House

The Jet Propulsion Laboratory's 50th anniversary of space exploration
will be the focus of a two-day open house at JPL on Saturday and
Sunday, July 16-17. 

The open house will run from 9 a.m. to 5 p.m. both days; admission is
free, and guests may park in Lab parking lots. 

Hosts at the Lab's main entrance will answer questions and direct
visitors to points of interest, which will include the Space Flight
Operations Facility and the Spacecraft Assembly Facility. Displays in
JPL's main mall will focus on ongoing projects representing the Lab's
work for NASA and other agencies. 

"Welcome to Outer Space," a multi-image production about JPL's
history, missions and future vision, will be shown in von Karman
Auditorium. Also, full-size models of the Voyager and Galileo
spacecraft and Galileo images of Earth, the Moon and asteroids will be
available for viewing in the adjacent museum. 

For additional information, contact JPL's Public Services Office on
extension 4-0112 or at mail stop 186-115. 

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% Date: Sat, 2 Jul 1994 15:04:42 +0700
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% Errors-To: [email protected]
% Reply-To: [email protected]
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% Subject: JPL Open House/Comet Shoemaker-Levy Activities
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon"  5-JUL-1994 08:37:56.04
CC:	
Subj:	New SL9 files

To : SL9 Mailing List

There are some new files in /pub/comet or /incoming at tamsun.tamu.edu
(128.194.15.32) :

jul1994.transit - Central meridian transit times and locations of 10 features 
                  on Jupiter southern hemisphere (July 1994)

galsat53.zip    - MSDOS program; displays locations of Jupiter's moons 
                  during the SL9 impacts (June 24, 1994 predictions
                  are used in the program)

tracker3.zip    - MSDOS program; displays the location of SL9 impact sites and
                  a few features on Jupiter's southern hemisphere

    Also, there is a GIF image of a crater chain on the farside of the
Moon taken by the Apollo 11 crew in 1969 at SEDS.LPL.Arizona.edu in
/pub/astro/SL9/images (moonchain.gif and moonchain.txt).  Thanks to
Martin Otterson for the information about this image.  See Q2.10 of
our FAQ list to find out how to get these files by email or I can mail
them to your account.   TRACKER and GALSAT have also been upload to
SEDS and America On-line (AOL Astronomy Archive; Comet Crash section).
   
Clear skies,
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .

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% Date: Tue, 5 Jul 1994 05:33:54 +0700
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% Subject: New SL9 files
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US2RMC::"[email protected]" "MAIL-11 Daemon"  6-JUL-1994 11:51:17.85
CC:	
Subj:	Comet/Jupiter Collision FAQ

To: SL9 Mailing List

The PostScript version will be uploaded to tamsun and SEDS shortly.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

                      Frequently Asked Questions about
            the Collision of Comet Shoemaker-Levy 9 with Jupiter

                          Last Updated 6-July-1994
                             10 Days to Impact
                                           
      Contact Dan Bruton ([email protected]) or John Harper ([email protected]) 
with comments, additions, corrections, etc.  A PostScript version of this 
FAQ list is available at tamsun.tamu.edu (128.194.15.32) in the /pub/comet 
directory.  To subscribe to the "Comet/Jupiter Collision Mailing List", send 
mail to [email protected] (no subject) with the message: 
SUBSCRIBE SL9 Firstname Lastname
            
RECENT CHANGES TO THIS FAQ LIST

        Question 1.4: More predictions
        Question 1.6: Live TV coverage
        Question 2.1: Updated impact times 
        Question 2.2 and 2.9: SARA
        Question 2.5: Apollo 11 image of a crater chain
        Question 2.10: New WWW sites and more articles

GENERAL QUESTIONS

 Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 Q1.2: Who are Shoemaker and Levy?
 Q1.3: Where can I find a GIF image of this comet?
 Q1.4: What will be the effects of the collision?
 Q1.5: Can I see the effects with my telescope?
 Q1.6: Will there be live coverage TV of the events?

SPECIFICS

 Q2.1: What are the impact times and impact locations?
 Q2.2: Can the collisions be observed with radio telescopes? 
 Q2.3: Will light from the explosions be reflected by any moons? 
 Q2.4: What are the orbital parameters of the comet? 
 Q2.5: Why did the comet break apart? 
 Q2.6: What are the sizes of the fragments? 
 Q2.7: How long is the fragment train? 
 Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions? 
 Q2.9: To whom can I report my observations? 
 Q2.10: Where can I find more information?

REFERENCES
ACKNOWLEDGMENTS

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

GENERAL QUESTIONS

Q1.1: Is it true that a comet will collide with Jupiter in July 1994?

     Yes, the shattered comet Shoemaker-Levy 9 will collide with Jupiter over 
a 5.6 day period in July 1994.  The first of 21 comet fragments is expected 
to hit Jupiter on July 16, 1994 and the last on July 22, 1994.  The 21 major 
fragments are denoted A through W in order of impact, with letters I and O 
not used.  All of the comet fragments will hit on the dark farside of Jupiter.  
The probability that all of the comet fragments will hit Jupiter is greater 
that 99.9%.  The probability that any fragment will impact on the near side 
as viewed from the Earth is < 0.01%.
     The impact of the center of the comet train is predicted to occur at a
Jupiter latitude of about -44 degrees at a point about 67 degrees east 
(toward the sunrise terminator) from the midnight meridian.  These impact 
point estimates from Chodas and Yeomans are only 5 to 9 degrees behind the 
limb of Jupiter as seen from Earth.  About 8 to 18 minutes after each 
fragment hits, the impact points will rotate past the limb.  After these 
points cross the limb it will take another 18 minutes before they cross the 
morning terminator into sunlight.                        


Q1.2: Who are Shoemaker and Levy?

   Comet Shoemaker-Levy 9 (1993e) was the ninth short-period comet discovered 
by Eugene and Carolyn Shoemaker and David H. Levy and was first identified on 
photographs taken on the night of 24 March 1993.   The photographs were taken 
at Palomar Mountain in Southern California with a 0.46 meter Schmidt camera 
and were examined using a stereomicroscope to reveal the comet [2,14].  The 
13.8 magnitude comet appeared 'squashed' in the original image.  Subsequent 
photographs taken by Jim Scotti with the Spacewatch telescope on Kitt Peak 
in Arizona showed that the comet was actually a shattered comet.  Some
astronomers call the comet a "string of pearls" since the comet fragments
are strung out in a line or train.
    Before the end of March 1993 it was realized that the comet had made a very
close approach to Jupiter in the summer of 1992.  At the beginning of April 
1993, after sufficient observations had been made to determine the orbit more 
reliably, Brian Marsden found that the comet is in orbit around Jupiter.  By 
late May 1993 it appeared that the comet was likely to impact Jupiter in 1994.  
Since then, the comet has been the subject of intensive study.  Searches of 
archival photographs have identified pre-discovery images of the comet from 
earlier in March 1993 but searches for even earlier images have been 
unsuccessful.  See [11] for more information about the discovery.


Q1.3: Where can I find a GIF image of this comet?

     GIF images can be obtained from SEDS.LPL.Arizona.EDU (128.196.64.66)
in the /pub/astro/SL9/images directory.  Below is a list of the images at
this site.  The files are listed here in reverse chronological order:

Comet1993eA.gif    March HST image of SL9 comet train
Comet1993eB.gif    Time comparison image of SL9 comet fragment
sl90216.gif        February 16, 1994 Image from Kitt Peak (J. Scotti)
wfpclevy.gif       Photo Montage of January 24-27 Imaging of SL9 from HST
sl9hst.gif         Post-fix HST Mosaic of SL9 (Jan. 24-27)
sl90121.gif        January 21, 1994 Image from Kitt Peak (R. Jedicke)
sl9compl.gif       Six month comparison image of SL9
1993eha.gif        View of the comet from HST
1993ehb.gif        From HST, focused on the center of the train of fragments
1993esw.gif        Ground-based view of the comet
sl03302b.gif       March 30, 1993 Image from Kitt Peak (J. Scotti)
sl9_930330.gif     March 30, 1993 image of SL9, Spacewatch, J. Scotti
sl9w_930328.gif    March 28, 1993 image of SL9
shoelevy.gif       An early GIF image of SL9
                                     
There are also other collision related GIF graphics and MPEG animations 
at SEDS.LPL.Arizona.EDU.  See Question 2.10 for other FTP and WWW sites.
Most of these sites will have images of Jupiter after the collisions.


Q1.4: What will be the effects of the collision?

     Jupiter will be about 770 million kilometers (480,000,000 miles) from
Earth, so it will be difficult to see the effects from Earth.  Also, 
the comet fragments will not effect Jupiter as a whole very much.  It will 
be like sticking 21 needles into an apple: "Locally, each needle does 
significant damage but the whole apple isn't really modified very much." [35].
The energy deposited by the comet fragments fall well short of the energy 
required to set off sustained thermonuclear fusion.  Jupiter would have to 
be more than 10 times more massive to sustain a fusion reaction.  
     Calculations by Paul Chodas (JPL) indicate that as seen from the Earth, 
the fragments will disappear behind the limb of Jupiter only 5 to 15 seconds 
before impact.  The later fragments will be visible closer to impact.  
Fragment W will disappear only 5 seconds before impact, at an altitude of only
about 200 km above the 1-bar pressure level: it may well start its bolide 
phase while still in view.  Furthermore, any sufficiently dense post-impact 
plume will have to rise only a few hundred kilometers to be visible from Earth.
     Simulations for 2-4 km fragments by Mark Boslough (Sandia National
Laboratories) indicate when the fireball resulting from an impact cools it 
would form a debris cloud that will rise hundreds of kilometers above the 
Jovian cloudtops, and would enter sunlight within minutes of the impact.  The 
arrival time of this giant cloud into sunlight would provide data on its 
trajectory, which in turn would help us know how big the comet fragment was.  
It is possible that it would be big (bright) enough to be seen by amateurs 
[42,43].  
     If the fragments are 2-4 km in diameter then the probability is very high
that these effects will be visible for some of the later impacts (e.g. W and R,
visible from Hawaii, S, visible from India and the far East, Q1 and Q2, visible
from Africa, parts of eastern Europe and the Middle East, L, Brazil and West 
Africa, K, South Pacific and Australia, and maybe even V, on the final night, 
visible in the Western half of the U.S.).  Observers in these locations are 
encouraged to anticipate the possibility of seeing the fireball within tens of
seconds after the impact, and a few minutes later after it has cooled, 
condensed, and entered the sunlight.  The apparent visible magnitude of any 
fireball will be similar to that of a Galilean satellite at best, but it would
appear redder.  They would be much brighter at infrared wavelengths.
     The following predictions by Mordecai-Mark Mac Low (University of Chicago)
are based on simulations for 1 km fragments:  Each comet fragment will enter
the Jupiter's atmosphere at a speed of 130,000 mph (60 km/s).  At an altitude 
of 100 km above the visible cloud decks, aerodynamic forces will overwhelm the
material strength of the fragment and tear it apart.  Five seconds after 
entry, the comet fragment would deposit its kinetic energy of around 10^28 ergs
(equivalent to around 200,000 megatons of TNT) at 100-150 km below the cloud 
layer [19].  Bigger fragments will have more energy and go deeper.
     The hot (30,000 K) gas resulting from a 1 km stopped comet will explode,
forming a fireball similar to a nuclear explosion, but much larger.  The 
visible fireball may only rise 100 km or so above the cloudtops in this case.
Above that height the density may drop so that it will become transparent.  
The fireball material will continue to rise, reaching a height of perhaps 
1000 km before falling back down to 300 km.  The fireball will spread out over
the top of the stratosphere to a radius of 2000-3000 km from the point of 
impact.  The top of the resulting shock wave will accelerate up out of the 
Jovian atmosphere in less than two minutes, while the fireball will be as 
bright as the entire sunlit surface of Jupiter for around 45 sec [18].  The 
fireball will be somewhat red, with a characteristic temperature of 2000 K - 
4000 K (redder than the sun, which is 5800 K).  Virtually all of the shocked 
cometary material will rise behind the shock wave, leaving the Jovian 
atmosphere and then splashing back down on top of the stratosphere at an 
altitude of 300 km above the clouds [unpublished simulations by Mac Low & 
Zahnle].  Not much mass is involved in this splash, so it will not be directly
observable.  The splash will be heavily enriched with cometary volatiles such 
as water or ammonia, and so may contribute to significant high hazes.
        Meanwhile, the downward moving shock wave will heat the local clouds,
causing them to buoyantly rise up into the stratosphere.  This will allow
spectroscopists to attempt to directly study cloud material, a unique
opportunity to confirm theories of the composition of the Jovian clouds.
Furthermore, the downward moving shock may drive seismic waves (similar to
those from terrestrial earthquakes) that might be detected over much of the
planet by infrared telescopes in the first hour or two after each impact.
The strength of these two effects remains a topic of research.  The
disturbance of the atmosphere will drive internal gravity waves ("ripples in
a pond") outwards.  Over the days following the impact, these waves will
travel over much of the planet, yielding information on the structure of
the atmosphere if they can be observed (as yet an open question).
     The "wings" of the comet will interact with the planet before and after
the collision of the major fragments.  The so-called "wings" are defined to
be the distinct boundary along the lines extending in both directions from 
the line of the major fragments; some call these 'trails'.  Sekanina, Chodas
and Yeomans have shown that the trails consist of larger debris, not dust: 
5-cm rock-sized material and bigger (boulder-sized and building-sized).  
Dust gets swept back above (north) of the trail-fragment line due to solar 
radiation pressure.  The tails emanating from the major fragments consist of
dust being swept in this manner.  Only the small portion of the eastern 
debris trail nearest the main fragments will actually impact Jupiter, 
according to the model, with impacts starting only a week before the major 
impacts.  The western debris trail, on the other hand, will impact Jupiter 
over a period of months following the main impacts, with the latter portion
of the trail actually impacting on the front side of Jupiter as viewed from
Earth.
     The injection of dust from the wings and tail into the Jovian system
may have several consequences.  First, the dust will absorb many of the
energetic particles that currently produce radio emissions in the Jovian
magnetosphere.  The expected decline and recovery of the radio emission may
occur over as long as several years, and yield information on the nature and
origin of the energetic particles.  Second, the dust may actually form a
second faint ring around the planet.
     Due to the great distance between Jupiter and the Earth, the comet 
poses no threat to Earth.  However, Eugene Shoemaker says that if a similar 
comet crashed on Earth it would be catastrophic:  "...we're talking about a 
million megatons of kinetic energy.  We're talking about the kind of event 
that is associated with mass extinction of species on Earth; really and truly 
a global catastrophe.  It might not take out the human race but it would 
certainly be very bad times." (CNN, Headline News)


Q1.5: Can I see the effects with my telescope?

     One might be able to detect atmospheric changes on Jupiter using
photography or CCD imaging.  It is important, however, to observe Jupiter
for several months in advance in order to know which features are due to
impacts and which are naturally occurring.  It appears more and more likely
that most effects will be quite subtle.  Without a large ( > 15" ?) telescope
and good detector, little is likely to be seen.
     It is possible that the impacts may create a new, temporary storm at the
latitude of the impacts.  Modeling by Harrington et al. suggests this is
possible [30].  The fragments of comet Shoemaker-Levy 9 will strike just
south of the South South Temperate Belt of Jupiter.  If the nuclei penetrate 
deep enough, water vapor may shoot high into the atmosphere where it could 
turn into a bluish shroud over a portion of the South South Temperate Zone 
[31].
     Impacts of the largest fragments may create one or two features.  A spot
might develop that could be a white or dark blue nodule and would likely have
a maximum diameter of 2,000 km to 2,500 km which in a telescope would be 1
to 1.5 arcseconds across.  This feature would be very short-lived with the
impact site probably returning to normal after just a few rotations of 
Jupiter.  A plume might also develop that would look dark against the South
Temperate Zone's white clouds or could appear as a bright jet projected from
Jupiter limb [31].  The table below shows the approximate sizes of features
that already exist on Jupiter for comparison.

 +==================================================================+ 
 |          FEATURE                            SIZE ESTIMATES       | 
 +==================================================================+
 |       Great Red Spot                       26000 by 11000 km     |
 |     White Spots FA,BC,DE                   9000 km               |
 |  Shadows of Io, Europa, and Ganymede       4300, 4200, 7100 km   |
 +==================================================================+

     Below is a list of files available at tamsun.tamu.edu in the /pub/comet
directory that may be helpful in identifying features on Jupiter:

tracker3.zip      MSDOS program that displays the location of impact sites
                  and features of Jupiter
jupe.description  Description of a PC program showing features of Jupiter
jul1994.transit   Transit Times for Red Spot and White Spots for July 1994
jul1994.moons     Jovian Moon events for July 1994 (Shadows, Eclipses, etc.)

    Also, there are little anticyclonic ovals at jovicentric latitudes of 
about -45 degrees which are typical of the South South Temperate domain
and are about 3500 km in diameter.  There are usually 6 or 7 around the planet
and they move with the South South Temperate current, i.e. faster than BC and 
DE.  See Sky & Telescope for a CCD image of these ovals by Don Parker [38].


Q1.6: Will there be live coverage TV of the events?

        NASA's coverage of the impact of Comet P/Shoemaker-Levy 9 during 
the week of July 16-22 includes a series of live, televised press briefings 
and a 24-hour newsroom operation at the Goddard Space Flight Center (GSFC), 
Greenbelt, Md.  The briefing panels will include Comet co-discoverers Drs. 
Eugene and Carolyn Shoemaker and David Levy on most days as well as scientists
presenting images and information from the Hubble Space Telescope and other 
spacecraft.  Dr. Lucy McFadden will have a round-up of observations from 
ground-based observatories around the world.  The program and briefing 
schedule follows:

JULY DATE       TIME (EDT)      EVENT
Sat.    16      10:00 p.m.      Live from HST: First Impact Image Release
Sun.    17      8:00 a.m.       Press Briefing at GSFC
Mon.    18      8:00 a.m.       Press Briefing at GSFC
Tue.    19      8:00 a.m.       Press Briefing at GSFC
Wed.    20      12:00 noon      Press Briefing at GSFC
Th.     21      8:00 a.m.       Press Briefing at GSFC
Fri.    22      9:30 a.m.       Press Briefing at GSFC
Sat.    23      8:00 a.m.       Press Briefing at GSFC
                                                     
Note:  The above times are dependent on the STS-65 mission schedule.  If 
there is a change in the launch or landing time of the Shuttle, the program 
times will change.  Video Uplink Schedule: NASA will provide feeds of b-roll 
and animation of the comet impacts with Jupiter on the following schedule:

June 29:        10:00 a.m. and 1:30 p.m. EDT
June 30:        10:30 a.m. and 1:30 p.m. EDT
 July 5:        10:30 a.m. and 1:30 p.m. EDT
July 15:        1:00 p.m. EDT

     Also on July 5, NASA Television will replay the May 18 press briefing 
with panelists Dr. Eugene Shoemaker, Dr. Heidi Hammell, Dr. Hal Weaver, 
Dr. Lucy McFadden and Dr. Melissa McGrath.  NASA TV is carried on Spacenet 2, 
transponder 5, channel 9, 69 degrees West, transponder frequency is 3880 MHz, 
audio subcarrier is 6.8 MHz, polarization is horizontal.
     Note also that your local PBS station will normally pick up one 
of the live feeds listed below so that you will see it at 10:30-11:30 
local time.  If you have a TVRO satellite dish you can watch it 5 times.
                                                                        
"THE GREAT COMET CRASH"
Wednesday July 20, 1994   (into early Thursday morning 7/21)
10:30pm - 11:30pm     Telstar 401-Ku 6 (PBS Schedule B)
11:30pm - 12:30am     Telstar 401-Ku 6 (PBS Schedule B)
12:30am - 1:30 am     Telstar 401-Ku 6 (PBS Schedule B)
 1:30am - 2:30 am     Telstar 401-Ku 7 (PBS Schedule C)
 2:30am - 3:30 am     Telstar 401-Ku 5 (PBS Schedule A)
 2:30am - 3:30 am     Telstar 401-C band 8 (PBS Schedule X)
                                                                 
    Also, there is a gathering of professional and amateur astronomers every 
week on the IRC (Internet Relay chat) channel #Astronomy for real time 
discussions.  Friday and Sunday sessions are held at 20:00 UT.  There may be 
continuous discussion/updates on the IRC channel #Astronomy during the impacts.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

SPECIFICS

Q2.1: What are the impact times and impact locations?

This information was provided P.W. Chodas and D.K. Yeomans:
==============================================================================

  Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
  ---------------------------------------------------------------

  P.W. Chodas, D.K. Yeomans and Z. Sekanina (JPL/Caltech)
  P.D. Nicholson (Cornell)

  Predictions as of 1994 July 5
  Date of last astrometric data in these solutions: 1994 July 4


The predictions for all fragments except Q2 are based on independent orbit
solutions; our orbit reference identifier is given.  The orbit solution
for fragment Q2 was obtained by applying a disruption model to the orbit
for Q1, and using astrometric measurements of Q2 relative to Q1.

Except for fragment Q2, uncertainties in the impact parameters are given
immediately below the predicted values.  These uncertainties are 1-sigma
values obtained from Monte Carlo analyses; we have made an effort to make
them realistic: they are not formal uncertainty values.  NOTE: To obtain a
95% confidence level, one should use a +/- 2 sigma window around the
predicted values.  The uncertainties for Q2 have not been quantified, but
are probably comparable to those for fragment T.

The dynamical model used for these predictions includes perturbations due to
the Sun, planets, Galilean satellites and the oblateness of Jupiter.  The
planetary ephemeris used was DE245.

-------------------------------------------------------------------------------
Frag-    Impact       Jovicentric  Merid.  Angle          Satellite Longitudes
  ment  Date/Time     Lat.  Long.  Angle   E-J-F  Orbit     at Impact  (deg)
       July  (UTC)    (deg) (deg)  (deg)   (deg)   Ref.  Amal   Io   Eur   Gany
------------h--m--s------------------------------------------------------------
A = 21  16 19:53:40  -43.08  175   64.05   99.04   A18   203t  344   106+   76+
               8.4      .19    5     .77     .57           4     1     1     0

B = 20  17 02:49:03  -43.04   67   63.54   99.40   B17    52+   42+  136+   91+
               8.3      .20    5     .75     .56           4     1     1     0

C = 19  17 06:55:36  -43.22  215   64.85   98.42   C14   175t   77+  153+   99+
               8.4      .17    5     .74     .55           4     1     1     0

D = 18  17 11:41:50  -43.45   27   65.27   98.08   D16   319   117+  173   109+
               8.7      .18    5     .77     .57           4     1     1     0

E = 17  17 15:03:51  -43.42  149   65.78   97.72   E31    61+  146+  187   117+
               8.0      .08    5     .48     .34           4     1     1     0

F = 16  18 00:28:15  -43.52  131   64.49   98.61   F22   344o  226   226   136+
               6.8      .12    4     .57     .41           3     1     0     0

G = 15  18 07:28:00  -43.58   23   66.60   97.09   G30   194t  286   255   151+
               5.7      .07    3     .38     .27           3     1     0     0

H = 14  18 19:25:48  -43.70   96   66.87   96.86   H29   194t   27+  305   176
               5.6      .07    3     .38     .27           3     1     0     0

K = 12  19 10:17:58  -43.77  275   67.76   96.21   K30   282   152+    8+e 207
               6.5      .07    4     .40     .28           3     1     0     0

L = 11  19 22:06:58  -43.88  343   68.11   95.93   L31   278   253    59+  232
               6.1      .07    4     .39     .28           3     1     0     0

N = 9   20 10:18:37  -44.19   65   67.80   96.09   N19   285   356 o 111+  257
               8.6      .12    5     .68     .48           4     1     1     0

P2= 8b  20 15:05:10  -44.53  240   66.40   97.01   P17    69+   37+  132+  267
               7.4      .09    4     .59     .41           4     1     1     0

Q2= 7b  20 19:31:36  -44.31   39   68.86   95.32         202t   74+  150+  277

Q1= 7a  20 19:59:04  -44.02   55   69.28   95.07   Q34   216    78+  152+  278
               7.3      .07    4     .41     .29           4     1     1     0

R = 6   21 05:22:04  -44.05   35   69.28   95.06   R28   138   157   191   297
               7.2      .08    4     .47     .33           4     1     1     0

S = 5   21 15:07:13  -44.13   28   69.72   94.73   S38    72+  240   232   318
               6.9      .08    4     .42     .29           3     1     0     0

T = 4   21 18:04:14  -44.99  138   67.37   96.23   T12   161t  266   244   324
              15.2      .16    9    1.00     .70           8     2     1     1

U = 3   21 21:47:00  -44.47  271   68.68   95.41   U13   273   297   259   332
              16.1      .19   10    1.13     .79           8     2     1     1

V = 2   22 03:57:25  -44.31  135   68.43   95.60   V13    99+  349   285   345
              12.4      .17    7    1.00     .71           6     2     1     0

W = 1   22 07:53:17  -44.17  276   70.23   94.36   W30   217    23+  302   353
               9.1      .10    6     .53     .37           5     1     1     0

Satellite Codes:  +  impact is visible from satellite
                  o  satellite is occulted by Jupiter at impact
                  e  satellite is eclipsed but not occulted at impact
                  t  satellite is in transit across Jupiter
-------------------------------------------------------------------------------

Notes:
1. Fragments J=13, M=10, and P1=8a are omitted because they have faded from
   view.  The March'94 HST images show that P2=8b and G=15 have split; we do
   not have sufficient data to obtain independent predictions for the
   sub-components.

2. The impact date/time is the time the impact would be seen at the Earth
   (if the limb of Jupiter were not in the way); the date is the day in
   July 1994; the time is given as hours and minutes of Universal Time.
   The impact time uncertainty is a 1-sigma value in minutes.

3. The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

4. The impact longitude is System III, measured westwards on the planet. The
   large uncertainty in impact longitudes is due to Jupiter's fast rotation.

5. The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.  This relative
   longitude is known much more accurately than the absolute longitude.
   At the latitude of the impacts, the Earth limb is at meridian angle 76 deg
   and the terminator is at meridian angle 87 deg.

6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact.  All impacts will be just on the
   farside as viewed from Earth; later impacts will be closer to the limb.

7. Satellite longitudes are given for Amalthea, Io, Europa, and Ganymede.
   The longitudes are measured east from superior conjunction (the anti-Earth
   direction).  Longitude uncertainties listed as "0" are simply < 0.5 deg.

8. According to these predictions, the only impact certain to occur during a
   satellite eclipse is K=12 with Europa eclipsed.

[Courtesy of Paul Chodas, JPL]

==============================================================================
     
     The angle of incidence of the impacts is between 41 and 42 degrees for 
all the fragments.   See "impacts.*" at SEDS.LPL.Arizona.EDU in the 
/pub/astro/SL9/info directory for updates.  The following are the 1-sigma 
(uncertainty) predictions for the fragment impact times:

               on March 1         -  30 min
               on May 1           -  24 min
               on June 1          -  16 min
               on July 1          -  10 min
               on July 15         -   6 min
               at impact - 18 hr  -   3 min

The time between impacts is thought to be known with more certainty than the
actual impact times.  This means that if somehow the impact time of the first
fragment can be measured experimentally, then impact times of the fragments
that follow can be predicted with more accuracy.

-----------------------------------------------------------
Fragment    Impact Time        Best Locations for Viewing
               (PDT)             Jupiter at Impact Time
-----------------------------------------------------------
   A     July 16 12:30 p.m.    Africa (except W. Africa),
                                Middle East, Eastern Europe
   B              7:34 p.m.    Eastern N. America, Mexico,
                                Western S. America
   C             11:49 p.m.    New Zealand, Hawaii

   D     July 17  4:13 a.m.    Australia, New Zealand,
                                Japan
   E              8:10 a.m.    India, Southern China,
                                S.E. Asia, Western Australia
   F              5:12 p.m.    S. America

   G     July 18 12:30 a.m.    New Zealand, Hawaii

   H             12:26 p.m.    Africa (except W. Africa),
                                Middle East, Eastern Europe
   K     July 19  3:21 a.m.    Australia, New Zealand

   L              3:18 p.m.    Brazil, W. Africa, Spain

   N     July 20  3:08 a.m.    Australia, New Zealand

   P2             7:52 a.m.    India, Southern China,
                                S.E. Asia, Western Australia
   Q1             1:04 p.m.    Africa (except W. Africa),
   Q2            12:37 p.m.     Middle East, Eastern Europe
   R             10:31 p.m.    Hawaii, West coast N. America

   S     July 21  8:18 a.m.    India, Southern China,
                                S.E. Asia, Western Australia
   T             11:01 a.m.    Africa (except W. Africa),
                                Middle East, Eastern Europe
   U              2:52 p.m.    Brazil, W. Africa, Spain

   V              8:44 p.m.    Western U.S., Mexico

   W     July 22  1:12 a.m.    New Zealand, Hawaii,
                                Eastern Australia          
-----------------------------------------------------------


Q2.2: Can the collision be observed with radio telescopes?

     The cutoff of radio emissions due to the entry of cometary dust into the
Jovian magnetosphere during the weeks around impact may be clear enough to be
detected by small radio telescopes.  Furthermore, impacts may be directly
detectable in radio frequencies.  Some suggest to listen in on 15-30 MHz 
during the comet impact.  So it appears that one could use the same antenna
for both the Jupiter/Io phenomenon and the Jupiter/comet impact.  There is 
an article in Sky & Telescope magazine which explains how to build a simple
antenna for observing the Jupiter/Io interaction [4,24,25].  
     For those interested in radio observations during the SL9 impact, 
Leonard Garcia of the University of Florida has made some information 
available.  The following files are available via anonymous ftp on the 
University of Florida, Department of Astronomy site astro.ufl.edu in the
/pub/jupiter directory:

  README.DOC      Explanation of predicted Jupiter radio storms tables
  jupradio.txt    Jovian Decametric Emission and the SL9/Jupiter Collision
  july94.txt      Tables of predicted Jupiter radio storms for July 1994

    The antenna required to observe Jupiter may be as simple as a dipole
antenna constructed with two pieces of wire 11 feet 8.4 inches in length,
connected to a 50 ohm coax cable.  This antenna should be laid out on a
East-West line and raised above the ground by at least seven feet.  A
Directional Discontinuity Ring Radiator (DDRR) antenna is also easy to
construct and can be made from 1/2 inch copper tubing 125.5 inches in
length (21Mhz).   The copper tube should be bent into a loop and placed 5
inches above a metallic screen.   A good preamp is required for
less sensitive shortwave receivers [39].
     Society of Amateur and Radio Astronomers (SARA) say that amateur radio 
astronomers may have to wait approximately three hours after impact for the
impact sites to rotate to the central meridian of Jupiter before anything 
unusual is detected.  This wait is typical due to the Jovian decametric 
synchrotron emissions being emitted as a beam of radiation.  Due to the 
large time differential from impact to radio observations any disturbance may 
have settled and not be detected.  SARA suggest that the radio observer 
begin the watch approximately 30 minutes before the fragments hit to four 
hour after.


Q2.3: Will light from the explosions be reflected by any moons?

     One may be able to witness the collisions indirectly by monitoring the
brightness of the Galilean moons that may be behind Jupiter as seen from
Earth.  One could monitor the moons using a photometer, a CCD camera.  However,
current calculations suggest that the brightenings may be as little as 0.05% 
of the sunlit brightness of the moon [18].  If a moon can be caught in eclipse
but visible from the earth during an impact, prospects will improve 
significantly.  According to current predictions, the only impact certain to 
occur during a satellite eclipse is K=12 with Europa eclipsed.  However, H=14 
and W=1 impact only about 2 sigma after Io emerges from eclipse at longitude 
20 deg, and B=20, E=17 and F=16 impact 0.5-2 sigma after Amalthea emerges from
eclipse at longitude 34 deg.  See also Q2.1 of this FAQ for satellite locations.
     The following files contain information concerning the reflection of 
light by Jupiter's moons and are available at SEDS.LPL.Arizona.EDU :
                                                            
galsat53.zip      MSDOS Program that Displays relative positions of
                      Jupiter's Moons during times of impact
impact_24apr.ps   PostScript Plot of impact times at satellite availability

     Also, monitoring the eclipses of the Galilean satellites after the
impacts may yield valuable scientific data with the moons serving as 
sensitive probes of any cometary dust in Jupiter's atmosphere.  The geometry
of the eclipses is such that the satellites pass through the shadow at 
roughly the same latitude as the predicted comet impacts.  There is an 
article in the first issue of CCD Astronomy involving these observations.  
The article says that if the dust were to obscure sunlight approximately 
120 kilometers above Jupiter's cloud tops, Io could be more that 3 percent 
(0.03 magnitudes) fainter than normal at mideclipse [40].


Q2.4: What are the orbital parameters of the comet?

     Comet Shoemaker-Levy 9 is actually in a temporary orbit of Jupiter, 
which is most unusual: comets usually just orbit the Sun.  Only two comets 
have ever been known to orbit a planet (Jupiter in both cases), and this was 
inferred in both cases by extrapolating their motion backwards to a time 
before they were discovered.  S-L 9 is the first comet observed while orbiting
a planet.  Shoemaker-Levy 9's previous closest approach to Jupiter (when it 
broke up) was on July 7, 1992; the distance from the center of Jupiter was 
about 96,000 km, or about 1.3 Jupiter radii.  The comet is thought to have 
reached apojove (farthest from Jupiter) on July 14, 1993 at a distance of 
about 0.33 Astronomical Units from Jupiter's center.  The orbit is very 
elliptical, with an eccentricity of over 0.998.  Computations by Paul Chodas, 
Zdenek Sekanina, and Don Yeomans, suggest that the comet has been orbiting 
Jupiter for 20 years or more, but these backward extrapolations of motion are 
highly uncertain.  See "elements.*" and "ephemeris.*" at SEDS.LPL.Arizona.EDU 
in /pub/astro/SL9/info for more information.
     In the abstract "The Orbit of Comet Shoemaker-Levy 9 about Jupiter"
by D.K. Yeomans and P.W. Chodas (1994, BAAS, 26, 1022), the elements
for the brightest fragment Q are listed.  These elements are Jovicentric
and for Epoch 1994Jul15 (J2000 ecliptic):

   1994 Periapses    Jul 20.7846           Arg. of periapses   43.47999
   Eccentricity      0.9987338             Long. of asc. node  290.87450
   Periapses dist.   34776.7 km            inclination         94.23333


Q2.5: Why did the comet break apart?

     The comet broke apart due to tidal forces on its closest approach to
Jupiter (perijove) on July 7, 1992 when it passed within the theoretical
Roche limit of Jupiter.  Shoemaker-Levy 9 is not the first comet observed
to break apart.  Comet West shattered in 1976 near the Sun [3].  Astronomers
believe that in 1886 Comet Brooks 2 was ripped apart by tidal forces near
Jupiter [2].  Several other comets have also been observed to have split 
[41].
     Furthermore, images of Callisto and Ganymede show crater chains which 
may have resulted from the impact of a shattered comet similar to Shoemaker-
Levy 9 [3,17].  The satellite with the best example of aligned craters is 
Callisto with 13 crater chains.  There are three crater chains on Ganymede.
These were first thought to be from basin ejecta; in other words secondary 
craters [27].  See SEDS.LPL.Arizona.edu in /pub/astro/SL9/images for images 
of crater chains (gipul.gif and chain.gif).
     There are also a few examples of crater chains on our Moon.  Jay Melosh
and Ewen Whitaker have identified 2 possible crater chains on the moon which
would be generated by near-Earth tidal breakup.  One is called the "Davy
chain" and it is very tiny but shows up as a small chain of craters aligned
back toward Ptolemaeus.  In near opposition images, it appears as a high
albedo line; in high phase angle images, you can see the craters themselves.
The second is between Almanon and Tacitus and is larger (comparable to the
Ganymede and Callisto chains in size and length).  There is an Apollo 11
image of a crater chain on the far side of the moon at SEDS.LPL.Arizona.edu
in /pub/astro/SL9/images (moonchain.gif).


Q2.6: What are the sizes of the fragments?

     Using measurements of the length of the train of fragments and a model
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the
parent nucleus of the comet (before breakup) was only about 2 km across [13].
This would imply that the individual fragments are no larger than about 500
meters across.  Images of the comet taken with the Hubble Space Telescope in
July 1993 indicate that the fragments are 3-4 km in diameter (3-4 km is an
upper limit based on their brightness; the fragments have visual magnitudes of
around 20).  A more elaborate tidal disruption model by Sekanina, Chodas and 
Yeomans [20] predicts that the original comet nucleus was at least 10 km in 
diameter.  This means the largest fragments could be 3-4 km across, a size 
consistent with estimates derived from the Hubble Space Telescope's July 1993 
observations.  
     The new images, taken with the Hubble telescope's new Wide Field and
Planetary Camera-II instrument in 1994, have given us an even clearer view 
of this fascinating object, which should allow a refinement of the size 
estimates.  Some astronomers now suggest that the fragments are about 1 km or 
smaller.  In addition, the new images show strong evidence for continuing 
fragmentation of some of the remaining nuclei, which will be monitored by 
the Hubble telescope over the next month.   


Q2.7: How long is the fragment train?

     The angular length of the train was about 51 arcseconds in March 1993 
[2].  The length of the train then was about one half the Earth-Moon 
distance.  In the day just prior to impact, the fragment train will stretch
across 20 arcminutes of the sky, more that half the Moon's angular diameter.
This translates to a physical length of about 5 million kilometers.  The 
train expands in length due to differential orbital motion between the first
and last fragments.  Below is a table with data on train length based on 
Sekanina, Chodas, and Yeomans's tidal disruption model:

           +=============================================+
           |    Date    Angular Length  Physical Length  |
           |               (arcsec)          (km)        |
           +=============================================+
           |  93 Mar 25       49            158,000      |
           |     Jul  1       67            265,000      |
           |  94 Jan  1      131            584,000      |
           |     Feb  1      161            669,000      |
           |     Mar  1      200            762,000      |
           |     Apr  1      255            893,000      |
           |     May  1      319          1,070,000      |
           |     Jun  1      400          1,366,000      |
           |     Jul  1      563          2,059,000      |
           |     Jul 15      944          3,593,000      |
           |    Impact A    1286          4,907,000      |
           +=============================================+


Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?

     The Hubble Space Telescope, like earthlings, will not be able to see the
collisions but will be able to monitor atmospheric changes on Jupiter.  The 
impact points are favorable for viewing from spacecraft: it can now be stated 
with certainty that the impacts will all be visible to Galileo, and now at 
least some impacts will be visible to Ulysses.  Although Ulysses does not have
a camera, it will monitor the impacts at radio wavelengths.
     Galileo will get a direct view of the impacts rather than the grazing
limb view previously expected.  The Ida image data playback was scheduled to
end at the end of June, so there should be no tape recorder conflicts with
observing the comet fragments colliding with Jupiter.  The problem is how to
get the most data played back when Galileo will only be transmitting at 10 
bps.  One solution is to have both Ulysses and Galileo record the event and
and store the data on their respective tape recorders.  Ulysses observations
of radio emissions data will be played back first and will at least give 
the time of each comet fragment impact.  Using this information, data can 
be selectively played back from Galileo's tape recorder.  From Galileo's 
perspective, Jupiter will be 60 pixels wide and the impacts will only show 
up at about 1 pixel, but valuable science data can still collected in the 
visible and IR spectrum along with radio wave emissions from the impacts.  
     The impact points are also viewable by both Voyager spacecraft, 
especially Voyager 2.  Jupiter will appear as 2.5 pixels from Voyager 2's 
viewpoint and 2.0 pixels for Voyager 1.  However, it is doubtful that the 
Voyagers will image the impacts because the onboard software that controls 
the cameras has been deleted, and there is insufficient time to restore and
test the camera software.  The only Voyager instruments likely to observe 
the impacts are the ultraviolet spectrometer and planetary radio astronomy 
instrument.  Voyager 1 will be 52 AU from Jupiter and will have a near-limb
observation viewpoint.  Voyager 2 will be in a better position to view the 
collision from a perspective of looking down on the impacts, and it is also 
closer at 41 AU.


Q2.9: To whom can I report my observations?

     Observation forms by Steve Lucas are available via ftp at 
oak.oakland.edu in the /pub/msdos/astrnomy directory.  These forms also 
contain addresses of "Jupiter Watch Program" section leaders.  jupcom02.zip
contains Microsoft Write files.  The Association of Lunar and Planetary 
Observers (ALPO) will also distribute a handbook to interested observers.  
The handbook "The Great Crash of 1994" is available for $10 by ALPO Jupiter 
Recorder, Phillip W. Budine, R.D. 3, Box 145C, Walton, NY 13856 U.S.A.  The 
cost includes printing, postage and handling.
     John Rogers, the Jupiter Section Director for the British Astronomical
Association, will be collecting data from regular amateur Jupiter observers
in Britain and worldwide.  He can be reached via email ([email protected])
or fax (UK [223] 333840).  The Society of Amateur and Radio Astronomers (SARA)
is collecting radio observations of the events.  Observations can be sent to 
the chairman of the SARA Comet Watch Committee: Tom Crowley, 3912 Whittington
Drive, Altanta, GA 30342, EMAIL : [email protected].


Q2.10: Where can I find more information?

   The SL9 educator's book put out by JPL is in the /pub/astro/SL9/EDUCATOR
directory of SEDS.LPL.Arizona.edu.  There are two technical papers [18,19] 
on the atmospheric consequences of the explosions available at 
oddjob.uchicago.edu in the /pub/jupiter directory.  There are some PostScript 
images and text files involving the results of fireball simulations by 
Sandia National Laboratories at tamsun.tamu.edu (128.194.15.32) in the 
/pub/comet/sandia directory.
    SEDS (Students for the Exploration and Development of Space) has set up
an anonymous account which allows you to use "lynx" - a VT100 WWW browser.
To access this service, telnet to SEDS.LPL.Arizona.EDU and login as "www"
(no password required).  This will place you at the SEDS home page, from 
which you can select Shoemaker-Levy 9.  A similar "gopher" interface is 
available at the same site.  Just login as "gopher".
     Below is a list of FTP and WWW sites with SL9 information:

===============================================================================
     SITE NAME         IP ADDRESS       DIRECTORY                 CONTENTS
===============================================================================
SEDS.LPL.Arizona.EDU (128.196.64.66)  /pub/astro/SL9           Images & Info
oddjob.uchicago.edu                   /pub/jupiter                 Articles
jplinfo.jpl.nasa.gov (137.78.104.2)   /news and /images            Images
ftp.cicb.fr          (129.20.128.34)  /pub/Images/ASTRO/hst        Images
tamsun.tamu.edu      (128.194.15.32)  /pub/comet               Images & Info

===============================================================================
                            WORLD WIDE WEB SITES             
===============================================================================
         http://seds.lpl.arizona.edu/sl9/sl9.html                          
         http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html      
         http://pscinfo.psc.edu/research/user_research/user_research.html 
         http://cea-ftp.cea.berkeley.edu/Jupiter/
         http://http.hq.eso.org/educnpubrelns/comet.html

     If you have only mail access then try mailing the following message
(no subject) to [email protected]:

ftp SEDS.LPL.Arizona.EDU
user anonymous [email protected]
cd pub
cd astro
cd SL9
dir
cd info
dir
get factsheet.txt

     Use your email address in the place of "[email protected]".  The file 
"factsheet.txt" should then be mailed to your account.  Other files 
can be retrieved in a similar manner.  For more information about this 
service mail just the word "HELP" or "HOWTOFTP" to [email protected].

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

REFERENCES

[1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
[2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
      page 38-39.
[3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
      chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
[4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
[5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
[6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
[7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
[8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
      September 1993, page 18.
[9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
[10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
[11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
[12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
      of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
[13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
      Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
[14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
      January 1994, page 40-44.
[15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
[16] "AstroNews", Astronomy, January 1994, page 19.
[17] "AstroNews", Astronomy, February 1994, page 16.
[18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
      Comet Shoemaker Levy 9", Icarus, Vol 108, page 1.
[19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
      Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
      submitted to Astrophysical Journal (Letters) on 7 June 1994.
[20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the
     Appearance of Periodic Comet Shoemaker-Levy 9", Astronomy &
     Astrophysics, in press.
[21] "On a collision Course with Jupiter", Mercury, Nov-Dec 1993, page 15-16.
[22] "Timing the Crash", Sky & Telescope, February 1994, page 11.
[23] "Capturing Jupiter on Video" Sky & Telescope, September 1993, page 102.
[24] North, Gerald, "Advanced Amateur Astronomy", page 296-298, (1991).
[25] "Backyard Radio Astronomy", Astronomy, March 1983, page 75-77.
[26] Harrington, J., R. P. LeBeau, K. A. Backes, and T. E. Dowling,
     "Dynamic response of Jupiter's atmosphere to the impact of comet
     Shoemaker-Levy 9" Nature 368: 525-527 (1994).
[27] David Morrison, "Satellites of Jupiter", page 392, (1982).
[28] Weaver, H. A., et al, "Hubble Space Telescope Observations of Comet 
     P/Shoemaker-Levy 9 (1993e).", Science 263, page 787-791, (1994).
[29] Duffy, T.S., W.L. Vos, C.S. Zha, H.K. Mao, and R.J. Hemley.  "Sound
     Velocities in Dense Hydrogen and the Interior of Jupiter"  Science 263,
     page 1590-1593, (1994).
[30] Harrington, J., R. P. LeBeau, K. A. Backes, & T. E. Dowling, "Dynamic
     response of Jupiter's atmosphere to the impact of comet P/Shoemaker-
     Levy 9", Nature 368, page 525-527, April 7, 1994.
[31] Olivares, Jose, "Jupiter's Magnificent Show", Astronomy, April 1994,
     page 74-79.
[32] Schmude, Richard W., "Observations of Jupiter During the 1989-90
     Apparition", The Strolling Astronomer: J.A.L.P.O., Vol. 35, No. 3.,
     September 1991.
[33] "Comet heads for collision with Jupiter",Aerospace America,April 1994,
      page 24-29.
[34] "Comet Shoemaker-Levy 9 and Galilean Eclipses", CCD Astronomy, Spring
     1994, page 18-19.
[35] Reston, James Jr., "Collision Course", TIME, May 23, 1994, page 54-61.
[36] Benka, Stephen G., "Boom or Bust", Physics Today, June 1994, page 19-21.
[37] Beatty, Kelly and Levy, David H., "Awaiting the Crash - Part II", Sky
     & Telescope, July 1994, page 18-23.
[38] Alan M. MacRobert, "Observing Jupiter at Impact Time", Sky & Telescope,
     July 1994, page 31-35.
[39] Van Horn, Larry, "Countdown to the Crash", Monitoring Times, June 1994,
     page 10-13.
[40] Mallama, Anthony, "Comet Shoemaker-Levy 9 and Galilean Satellite
     Eclipses", CCD Astronomy, Spring 1994, pages 18-19.
[41] B. M. Middlehurst and G. P. Kuiper, "The Moon, Meteorites
     and Comets",  Univ. Chicago Press, 1963.
[42] Boslough, Mark B., et al, "Mass and Penetration Depth of Shoemaker-Levy 9
     fragments from time-resolved photometry", Geophysical Research Letters 
     (in press), June 1994.
[43] Crawford, David A., et al, "The impact of Comet Shoemaker-Levy 9 on
     Jupiter", Shock Waves (in press) April 1994.
[44] Bruning, David, "The Comet Crash", Astronomy (June 1994) pages 41-45.
[45] Levy, David, "Collision course! : A comet is bearing down on Jupiter"
     Smithsonian, Vol 25 No 3 (June 1994) pages 62-71.
[46] Stephens, Sally, "Smash it up!", Mercury, March-Arpil 1994, pages 7-11
[47] Boslough, M.B., D.A. Crawford, A.C. Robinson, T.G. Trucano, "Watching for
     fireballs on Jupiter", submitted to EOS, 1994.


ACKNOWLEDGMENTS

     Thanks to Ross Smith for starting a FAQ and to all those who have
contributed :  Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke,
Rik Hill, Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke,
David H. Levy, Eugene and Carolyn Shoemaker, Jim Scotti, Richard A.
Schumacher, Louis A. D'Amario, John McDonald, Michael Moroney, Byron
Han, Wayne Hayes, David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki,
Jeffrey A. Foust, Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina,
Don Yeomans, Richard Schmude, Lenny Abbey, Chris Lewicki, the Students
for the Exploration and Development of Space (SEDS), David A. Seal,
Leonard Garcia, Raymond Doyle Benge, Mark Boslough, Dave Mehringer,
John Spencer, Erik Max Francis, John Rogers, Al Jackson, Lucy-Ann A. 
McFadden, Michael F. A'Hearn, Martin Otterson, Tom Crowley, and many 
others who have discussed this event on newsgroups.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Clear skies,
                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .

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% Errors-To: [email protected]
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% Subject: Comet/Jupiter Collision FAQ
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% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "MAIL-11 Daemon"  6-JUL-1994 13:12:38.55
CC:	
Subj:	New predicted impact times

[Courtesy of Paul Chodas, JPL]

Below is the July 5 edition of our Predicted Impact Parameters table.

This set of predictions is particularly important because the Galileo
observation sequences will be keyed to the these impact times.  The orbit
solutions for these predictions were based on very recent astrometric
positions, some of them obtained as late as yesterday, July 4!  Helping
matters further, some of the new measurements were reduced using the pre-
release Hipparcos star catalog, making them highly accurate.  We thank the
many observers and measurers who worked long hours over the weekend to
provide us with the very latest data.

The predicted impact times are generally about 5 to 10 minutes earlier than
those in our table of June 24, at least for the major fragments.  The times
for fragments A and D made the largest jumps (24 and 29 minutes later), and
the time for W jumped 19 minutes earlier.  Jumps like these are generally
due to small measurement errors in the latest data used in the solution.
Because of the new data, the impact time uncertainties have dropped
substantially, down into the 6-8 minute range for many of the fragments.
We expect future jumps in predicted impact times to be correspondingly
smaller.

Starting with this version of the table, we provide impact times to the
nearest second, even though that is well below our current level of accuracy,
and we provide impact time uncertainties to the nearest tenth of a minute.

Paul Chodas
1994 July 5

==============================================================================

  Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
  ---------------------------------------------------------------

  P.W. Chodas, D.K. Yeomans and Z. Sekanina (JPL/Caltech)
  P.D. Nicholson (Cornell)

  Predictions as of 1994 July 5
  Date of last astrometric data in these solutions: 1994 July 4

The predictions for all fragments except Q2 are based on independent orbit
solutions; our orbit reference identifier is given.  The orbit solution
for fragment Q2 was obtained by applying a disruption model to the orbit
for Q1, and using astrometric measurements of Q2 relative to Q1.

Except for fragment Q2, uncertainties in the impact parameters are given
immediately below the predicted values.  These uncertainties are 1-sigma
values obtained from Monte Carlo analyses; we have made an effort to make
them realistic: they are not formal uncertainty values.  NOTE: To obtain a
95% confidence level, one should use a +/- 2 sigma window around the
predicted values.  The uncertainties for Q2 have not been quantified, but
are probably comparable to those for fragment T.

The dynamical model used for these predictions includes perturbations due to
the Sun, planets, Galilean satellites and the oblateness of Jupiter.  The
planetary ephemeris used was DE245.

-------------------------------------------------------------------------------
Frag-    Impact       Jovicentric  Merid.  Angle          Satellite Longitudes
  ment  Date/Time     Lat.  Long.  Angle   E-J-F  Orbit     at Impact  (deg)
       July  (UTC)    (deg) (deg)  (deg)   (deg)   Ref.  Amal   Io   Eur   Gany
------------h--m--s------------------------------------------------------------
A = 21  16 19:53:40  -43.08  175   64.05   99.04   A18   203t  344   106+   76+
               8.4      .19    5     .77     .57           4     1     1     0

B = 20  17 02:49:03  -43.04   67   63.54   99.40   B17    52+   42+  136+   91+
               8.3      .20    5     .75     .56           4     1     1     0

C = 19  17 06:55:36  -43.22  215   64.85   98.42   C14   175t   77+  153+   99+
               8.4      .17    5     .74     .55           4     1     1     0

D = 18  17 11:41:50  -43.45   27   65.27   98.08   D16   319   117+  173   109+
               8.7      .18    5     .77     .57           4     1     1     0

E = 17  17 15:03:51  -43.42  149   65.78   97.72   E31    61+  146+  187   117+
               8.0      .08    5     .48     .34           4     1     1     0

F = 16  18 00:28:15  -43.52  131   64.49   98.61   F22   344o  226   226   136+
               6.8      .12    4     .57     .41           3     1     0     0

G = 15  18 07:28:00  -43.58   23   66.60   97.09   G30   194t  286   255   151+
               5.7      .07    3     .38     .27           3     1     0     0

H = 14  18 19:25:48  -43.70   96   66.87   96.86   H29   194t   27+  305   176
               5.6      .07    3     .38     .27           3     1     0     0

K = 12  19 10:17:58  -43.77  275   67.76   96.21   K30   282   152+    8+e 207
               6.5      .07    4     .40     .28           3     1     0     0

L = 11  19 22:06:58  -43.88  343   68.11   95.93   L31   278   253    59+  232
               6.1      .07    4     .39     .28           3     1     0     0

N = 9   20 10:18:37  -44.19   65   67.80   96.09   N19   285   356 o 111+  257
               8.6      .12    5     .68     .48           4     1     1     0

P2= 8b  20 15:05:10  -44.53  240   66.40   97.01   P17    69+   37+  132+  267
               7.4      .09    4     .59     .41           4     1     1     0

Q2= 7b  20 19:31:36  -44.31   39   68.86   95.32         202t   74+  150+  277

Q1= 7a  20 19:59:04  -44.02   55   69.28   95.07   Q34   216    78+  152+  278
               7.3      .07    4     .41     .29           4     1     1     0

R = 6   21 05:22:04  -44.05   35   69.28   95.06   R28   138   157   191   297
               7.2      .08    4     .47     .33           4     1     1     0

S = 5   21 15:07:13  -44.13   28   69.72   94.73   S38    72+  240   232   318
               6.9      .08    4     .42     .29           3     1     0     0

T = 4   21 18:04:14  -44.99  138   67.37   96.23   T12   161t  266   244   324
              15.2      .16    9    1.00     .70           8     2     1     1

U = 3   21 21:47:00  -44.47  271   68.68   95.41   U13   273   297   259   332
              16.1      .19   10    1.13     .79           8     2     1     1

V = 2   22 03:57:25  -44.31  135   68.43   95.60   V13    99+  349   285   345
              12.4      .17    7    1.00     .71           6     2     1     0

W = 1   22 07:53:17  -44.17  276   70.23   94.36   W30   217    23+  302   353
               9.1      .10    6     .53     .37           5     1     1     0

Satellite Codes:  +  impact is visible from satellite
                  o  satellite is occulted by Jupiter at impact
                  e  satellite is eclipsed but not occulted at impact
                  t  satellite is in transit across Jupiter
-------------------------------------------------------------------------------

Notes:

1. Fragments J=13, M=10, and P1=8a are omitted because they have faded from
   view.  The March'94 HST images show that P2=8b and G=15 have split; we do
   not have sufficient data to obtain independent predictions for the
   sub-components.

2. The impact date/time is the time the impact would be seen at the Earth
   (if the limb of Jupiter were not in the way); the date is the day in
   July 1994; the time is given as hours and minutes of Universal Time.
   The impact time uncertainty is a 1-sigma value in minutes.

3. The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

4. The impact longitude is System III, measured westwards on the planet. The
   large uncertainty in impact longitudes is due to Jupiter's fast rotation.

5. The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.  This relative
   longitude is known much more accurately than the absolute longitude.
   At the latitude of the impacts, the Earth limb is at meridian angle 76 deg
   and the terminator is at meridian angle 87 deg.

6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact.  All impacts will be just on the
   farside as viewed from Earth; later impacts will be closer to the limb.

7. Satellite longitudes are given for Amalthea, Io, Europa, and Ganymede.
   The longitudes are measured east from superior conjunction (the anti-Earth
   direction).  Longitude uncertainties listed as "0" are simply < 0.5 deg.

8. According to these predictions, the only impact certain to occur during a
   satellite eclipse is K=12 with Europa eclipsed.

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% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

    	The next note is over 2000 lines long.  You have been warned.
    

Article: 1041
From: [email protected] (Rob Landis)
Newsgroups: sci.astro.planetarium
Subject: IPS Comet/Jupiter Paper <very long>
Date: 7 Jul 1994 15:29:07 GMT
Organization: Space Telescope Science Institute, Baltimore MD
 
In order to better free up my time, I'm posting the paper I'll be
presenting at IPS next week.  This text is voluminous, but, should
help out in planning your Jupiter impact coverage. 
 
This is an updated version to what was posted on this site back in May. 
 
++Rob Landis
email: [email protected]
 
Due to the nature of the overwhelming requests I received at 
MAPS last week, I'm making this paper available on the Internet.  
Note it is sans illustrations.  Good luck!
 
++Rob Landis, STScI
  Moving Targets Group
 
email:  [email protected]

 
		IPS Conference
     Astronaut Memorial Planetarium & Observatory
                Cocoa, Florida
 
	       10-16 July 1994
 
   "Comet P/Shoemaker-Levy's Collision with Jupiter:  
Covering HST's Planned Observations from Your Planetarium"
 
Abstract:  Comet Shoemaker-Levy 9 (1993e) was discovered 
in March 1993.  Early ground-based observations indicated 
the comet had fragmented into several pieces.  The comet 
is in a highly inclined, elliptical orbit around Jupiter.  
P/Shoemaker-Levy 9 was tidally ripped apart during peri-
Jove in July 1992. The Hubble Space Telescope has provided 
the most detailed look to date and resolved 20 separate 
nuclei.  The nuclei are expected to slam into Jupiter over 
a five-day period beginning on 16 July 1994.  The total 
energy of the collisions will be equivalent to 100 million 
megatons of TNT (more than 10,000 times the total destruc-
tive power of the world's nuclear arsenal at the height of 
the Cold War).  An armada of spacecraft will observe the 
event:  Voyager 2, Galileo, IUE, Ulysses, and the Hubble 
Space Telescope.  HST will be the astronomical instrument 
of choice to observe P/SL9, and the after effects of the 
energy imparted into the Jovian atmosphere.  NASA Select 
television may provide planetarium patrons with a ringside 
seat of the unfolding drama at Jupiter.
 
 
		       Introduction
 
	The author and Steve Fentress (Strasenburgh Plane-
tarium) had remarkable success covering the Voyager 2/
Neptune encounter during August 1989 using existing NASA 
video and still images.  No special effects were needed -- 
nor used -- to bring Voyager 2's odyssey to the Upstate New 
York community.  During the first week of December 1993, 
several major planetaria achieved similar success in their 
coverage of the first servicing mission to the Hubble Space 
Telescope .  Another opportunity for planetaria to cover 
fast-breaking astronomical and space science news awaits 
this summer as P/Shoemaker-Levy 9 collides with Jupiter.  
What follows is background material on the HST, the comet,
Jupiter, and the planned observations of the upcoming collisions.
 
	Planetaria and science centers worldwide have a 
unique opportunity to be involved in the understanding 
and exploration of our solar system when you participate 
in the P/Shoemaker-Levy collision with Jupiter.  Public 
interest in your program will have been greatly stimulated 
before and during the series of collisions by daily televi-
sion broadcasts, newspapers, and magazines.  In certain 
areas of the nation, local cable companies will be carrying 
the NASA Select signal to further stimulate interest in the event.
 
	We at the Space Telescope Science Institute and 
National Aeronautics and Space Administration anticipate that 
the public interest will be extremely high and that you may 
expect large attendances at your location.
 
	Never before in modern times has a collision between 
two solar system bodies been observed.  The instrument of choice 
to observe this unique event will be the Hubble Space Telescope. 
 
  The Hubble Space Telescope:  Planned Observations of 
  Periodic Comet Shoemaker-Levy 9  (1993e) and Jupiter
 
	The Hubble Space Telescope is a NASA project with 
international cooperation from the European Space Agency 
(ESA).  HST is a 2.4-meter reflecting telescope which was 
deployed in low-Earth orbit (600 kilometers) by the crew of 
the space shuttle Discovery (STS-31) on 25 April 1990.
 
	Responsibility for conducting and coordinating the 
science operations of the Hubble Space Telescope rests with 
the Space Telescope Science Institute (STScI) on the Johns 
Hopkins University Homewood Campus in Baltimore, Maryland.  
STScI is operated for NASA by the Association of University 
for Research in Astronomy, Incorporated (AURA).
 
	HST's current complement of science instruments 
include two cameras, two spectrographs, and fine guidance 
sensors (primarily used for astrometric observations).  
Because of HST's location above the Earth's atmosphere, these
science instruments can produce high resolution images of 
astronomical objects.  Ground-based telescopes can seldom 
provide resolution better than 1.0 arc-seconds, except 
momentarily under the very best observing conditions.  
HST's resolution is about 10 times better, or 0.1 arc-seconds.
 
	It is generally expected that nearly every observatory 
in the world will be observing events associated with Comet 
Shoemaker-Levy's impacts on Jupiter.  Most observatories are 
setting aside time and resources but delaying detailed planning 
until the last possible minute in order to optimize their 
observations based on the latest theoretical predictions and 
the latest observations of the cometary properties.  Having the 
advantage of being above the Earth's turbulent atmosphere, HST 
is the astronomical spacecraft of choice to observe the unfolding 
drama of Comet P/Shoemaker-Levy 9 collision with Jupiter.  Other
spacecraft to observe the event include the International Ultra-
violet Explorer (IUE), Extreme Ultraviolet Explorer, Galileo, 
Voyager 2, Ulysses, and possibly others.
 
	From 16 July through 22 July 1994, pieces of an object 
designated as Comet P/Shoemaker-Levy 9 will collide with Jupiter, 
and may have observable effects on Jupiter's atmosphere, rings, 
satellites, and magnetosphere. Since this is the first collision 
of two solar system bodies ever to be observed, there is large 
uncertainty about the effects of the impact.  Shoemaker-Levy 9 
consists of nearly 20 discernible bodies with diameters estimated 
at 2 to 4 kilometers (km), depending on method of estimation and 
assumptions about the nature of the bodies, a dust coma surround-
ing these bodies, and an unknown number of smaller bodies.  All 
the large bodies and much of the dust will be involved in the 
energetic, high-velocity impact with Jupiter.   
 
	The Hubble Space Telescope has the capability of obtaining 
the highest resolution images of all observations and will continue 
to image the morphology and evolution of the comet until days before 
first fragments of the comet impact with Jupiter.  HST's impressive 
array of science instruments will study Jupiter, P/Shoemaker-Levy 
9, and the Jovian environs before, during, and after the collision 
events.  The objective of these observations is to better constrain 
astrometry, impact times,  fragment sizes, study the near-fragment 
region and perform deep spectroscopy on the comet.  During the 
collision events it is hoped that the HST will be able to image the 
fireball at the limb, and after collisions the atmosphere, rings, 
satellites, and magnetosphere will be monitored for changes caused 
by the collision.  The HST will devote approximately 18 hours of 
time with the Wide Field/Planetary Camera (WF/PC -- pronounced 
"wif-pik").  The disk of Jupiter will be about 150 pixels across 
in the images, a resolution of about 1000 km/pixel.
 
	The HST program that has been approved consists of 112 
orbits of observations of both the comet and Jupiter.  The obser-
vations will be made by six different teams.
 
 
Table 1: Science Observation Team (SOT) Principal Investigators for 
         the HST Jupiter Campaign.
 
 
Principal 	Science 	Target		Science Objectives
Investigator	Instrument
=======================================================================
_______________________________________________________________________
Hal Weaver	WFPC+FOS 	SL9		morphology, breakup,
(STScI) 					OH emission
_______________________________________________________________________
Heidi Hammel    WFPC            Jupiter  	seismic/gravity waves
(MIT)                                    	clouds and wind fields
_______________________________________________________________________
Keith Noll      FOS+HRS       	Jupiter  	composition changes 
(STScI)						at impact sites
_______________________________________________________________________
Melissa McGrath FOS+HRS       	magnetosphere   dust contamination
(STScI)                                         of magnetosphere
_______________________________________________________________________
John Clarke     WFPC+FOC      	Jupiter   	UV imaging of clouds 
(U Mich)                                        and aurorae
_______________________________________________________________________
Bob West        WFPC            Jupiter    	stratospheric haze
(JPL)
_______________________________________________________________________
 
Table 2:  HST Jupiter/Shoemaker-Levy Campaign Programs
 
o UV Observations of the Impact of Comet SL9 with Jupiter
o A Search for SiO in Jupiter's Atmosphere
o Abdundances of Stratospheric Gas Species from Jovian Impact Events
o SL9's Impact on the Jovian Magnetosphere
o Observations of Io's and Europa's Regions of Jovian Magnetosphere 
  for Cometary Products
o Dynamical Parameters of Jupiter's Troposphere and Stratosphere
o HST Observations of the SL9 Impacts on Jupiter's Atmosphere
o Comparison of Meterological Models with HST Images
o FUV Imaging of Jupiter's Upper Atmosphere
o Auroral Signature of the Interaction of SL9 with the Jovian Mag-
  netosphere
o HST Imaging Investigation of SL9
o Cometary Particles as Tracers of Jupiter's Stratospheric Circulation
 
A bit more than 1/3 of the observations will be of the comet with the 
remainder focused on Jupiter and environs.  The comet observations 
have already begun, the first being made in late January.  The next 
will be in late March, with three more observations spaced in time up 
to mid-July,  just before impact.  The Jupiter observations begin the 
week before impact.  The impact week has many observations, and followup
observations continue sporadically until late August. Details of the 
observing program are being finalized.
 
    Some Background on Comet Shoemaker-Levy 9 and Jupiter
 
	A comet, already split into many pieces, will strike the 
planet Jupiter in the third week of July of 1994.  It is an event 
of tremendous scientific interest but, unfortunately, one which is 
likely to be unobservable by the general public. Nevertheless, it 
is a unique phenomenon and secondary effects of the impacts will 
be sought after by both amateur and professional astronomers.
 
		     Significance
 
	The impact of Comet Shoemaker-Levy 9 onto Jupiter 
represents the first time in human history that people have 
discovered a body in the sky and been able to predict its 
impact on a planet more than seconds in advance.  The impact 
will deliver more energy to Jupiter than the largest nuclear 
warheads ever built, and up to a significant percentage of 
the energy delivered by the impact which is generally 
thought to have caused the extinction of the dinosaurs 
on Earth, roughly 65 million years ago.
 
			 History
 
	Periodic Comet Shoemaker-Levy 9 (1993e) is the ninth 
short-period comet discovered by husband and wife scientific 
team of Carolyn and Gene Shoemaker and amatuer astronomer David 
Levy.  The comet was photographically discovered on 24 March 
1993 with the 0.46-meter Schmidt telescope at Mt. Palomar.  
On the original image it appeared 'squashed'.  Subsequent con-
firmation photographs at a larger scale taken by Jim Scotti 
with the Spacewatch telescope on Kitt Peak showed that the 
comet was split into many separate fragments.  Scotti reported
at least five condensations in a very long, narrow train 
approximately 47 arc-seconds in length and and about 11 arc-
seconds in width, with dust trails extending from either end 
of the nuclear train.  Its discovery was a serendipitous product
of their continuing search for near-Earth objects.  Near-Earth 
objects are bodies whose orbits come nearer to the Sun than that 
of Earth and hence have some potential for collisions with Earth. 
 
	The International Astronomical Union's Central Bureau 
for Astronomical Telegrams immediately issued a circular, 
announcing the discovery of the new comet.  The comet's bright-
ness was reported as about 14th magnitude, more than a thousand 
times too faint to be seen with the naked eye.  Bureau director 
Brian G. Marsden noted that the comet was some 4 degrees from 
Jupiter and that its motion suggested that it could be near 
Jupiter's distance from the Sun.
                  
	Before the end of March it was realized that the 
comet had made a very close approach to Jupiter in mid-1992 
and at the beginning of April, after sufficient observations 
had been made to determine the orbit more reliably, 
Brian Marsden found that the comet is in orbit around Jupiter. 
 
	By late May it became apparent that the comet was 
likely to impact Jupiter in 1994.  Since then, the comet has 
been the subject of intensive study.  Searches of archival 
photographs have identified pre-discovery images of the comet 
from earlier in March 1993 but searches for even earlier 
images have been unsuccessful.
 
		Cometary Orbit
 
	According to the most recent computations, the comet 
passed less than 1/3 of a Jovian radius (120,000 km) above 
the clouds of Jupiter late on 7 July 1992 (UT).  The individual 
fragments separated from each other 1-1/2 hours after closest 
approach to Jupiter and they are all in orbit around Jupiter 
with an orbital period of about two years.  Calculations of the 
orbit prior to 7 July 1992 are very uncertain but it seems very 
likely that the comet was previously in orbit around Jupiter 
for two decades or more.  Ed Bowell and Lawrence Wasserman of 
the Lowell Observatory have integrated the best currently 
available orbit for P/Shoemaker-Levy 9  in a heliocentric 
reference frame, and noted that the calculations put the 
"comet" in a "Jupiter-grazing" orbit before about 1966.  
Wasserman and Bowell's possible Jupiter close approaches 
are in 2-, 3-, and 4-year intervals.                   
 
Table 3:  Possible Close Approaches of 1993e with Jupiter
 
	       Distance			  Year/Month/Date
 
	1993e 0.08963 AU from Jupiter on 1971   4   26.0       	  	
	1993e 0.06864 AU from Jupiter on 1975   4   26.8 
	1993e 0.07000 AU from Jupiter on 1977   5    7.0 
	1993e 0.11896 AU from Jupiter on 1980   2    1.8                       
	1993e 0.12453 AU from Jupiter on 1982   5   26.0                        
	1993e 0.11937 AU from Jupiter on 1984  10    4.5
	1993e 0.07031 AU from Jupiter on 1987   7   12.4               
	1993e 0.06090 AU from Jupiter on 1989   8    2.5                    
	1993e 0.00072 AU from Jupiter on 1992   7    8.0                       
	1993e         Impacts Jupiter on 1994   7   16.8
 
     
Because the orbit takes the comet nearly 1/3 of an astronomical 
unit (30 million miles) from Jupiter, the sun causes significant 
changes in the orbit.  Thus, when the comet again comes close to 
Jupiter in 1994 it will actually impact the planet, moving almost 
due northward at 60 km/sec aimed at a point only halfway from the 
center of Jupiter to the visible clouds.
 
	All fragments will hit Jupiter in the southern hemisphere, 
at latitudes near 45 degrees south, between 16 and 22 July 1994, 
approaching the atmosphere at an angle roughly 45 degrees from the 
vertical.  The times of the impacts are now known to within roughly 
20 minutes,  but continuing observations leading up to the impacts 
will refine the precision of the predictions.  The impacts will 
occur on the back side of Jupiter as seen from Earth; that is, 
out of direct view from the Earth (this also means that the comet 
will strike on Jupiter's nightside).  This area will be close to 
the limb of Jupiter and will be carried by Jupiter's rotation to 
the front,  illuminated side less than half an hour after the 
impact.  The grains ahead of and behind the comet will impact 
Jupiter over a period of four months, centered on the time of 
the impacts of the major fragments.  The grains in the tail of 
the comet will pass behind Jupiter and remain in orbit around 
the planet.
 
	        The Nature of the Comet
 
	The exact number of large fragments is not certain since 
the best images show hints that some of the larger fragments may 
be multiple.  At least 21 major fragments were originally identified.
No observations are capable of resolving the individual fragments 
to show the solid nuclei.  Images with the Hubble Space Telescope 
suggest that there are discrete, solid nuclei in each of the largest
fragments which, although not spatially resolved, produce a single, 
bright pixel that stands out above the surrounding coma of grains.  
Reasonable assumptions about the spatial distribution of the grains 
and about the reflectivity of the nuclei imply sizes of 2 to 4 km 
(diameter) for each of the 11 brightest nuclei.  Because of the 
uncertainties in these assumptions, the actual sizes are very un-
certain and there is a small but not negligible possibility that 
the peak in the brightness at each fragment is due not to a nucleus 
but to a dense cloud of grains.
 
	No outgassing has been detected from the comet but 
calculations of the expected amount of outgassing suggest that 
more sensitive observations are needed because most ices vaporize 
so slowly at Jupiter's distance from the sun.  The spatial distri-
bution of dust suggests that the material ahead of and behind the 
major fragments in the orbit are likely large particles from the 
size of sand up to boulders.  The particles in the tail are very 
small, not much larger than the wavelength of light.  The bright-
nesses of the major fragments were observed to change by factors 
up to 1.7 between March and July 1993, although some became brighter 
while others became fainter.  This suggests intermittent release of 
gas and grains from the nuclei.
 
	Studies of the dynamics of the breakup suggest that the 
structural strength of the parent body was very low and that the 
parent body had a diameter of order 5 km.  This is somewhat 
smaller than one would expect from putting all the observed 
fragments back together but the uncertainties in both estimates 
are large enough that there is no inconsistency.
 
		  Crater Chains
 
	Although none of the fragments will hit any of Jupiter's 
large satellites, Voyager data indicate that tidally split comets 
have hit the Galilean satellites in the past.  Until the discovery 
of Comet P/Shoemaker-Levy 9, the strikingly linear crater chains 
on Callisto and Ganymede had remained unexplained.  It is quite 
likely that these crater chains were formed by comets similar to P/SL9.
 
	The longest of the chains, is 620 km long and comprises 
25 craters.  The first interpretation hinted that these were 
secondary impact chains, formed by material ejected from large 
basins -- very much akin to the Earth's Moon.  The Callisto chains 
are much straighter and more uniform than most secondary chains.
For 15 years the crater chains remained unexplained.  In light of 
P/SL9's nature, it is logical to conclude that the crater chains 
on Callisto (and Ganymede) were formed when tidally disrupted 
comets impacted the Jovian satellites.
 
	To date, thirteen crater chains have been identified on 
Callisto.  Upon recent re-examination of Voyager's data, three 
more similar chains have now been identified on Ganymede.  The 
next opportunity to identify and re-examine these features will 
be when the Galileo spacecraft enters Jovian orbit in December, 1995.
 
		The Planet Jupiter
 
	Jupiter is the largest of the nine known planets, almost 
11 times the diameter of Earth and more than 300 times its mass.  
In fact, the mass of Jupiter is almost 2.5 times that of all the 
other planets combined. Being composed largely of the light elements 
hydrogen (H) and helium (He), its mean density is only 1.3 times 
that of water.  The mean density of Earth is 5.2 times that of 
water. The pull of gravity on Jupiter at the top of the clouds 
at the equator is 2.4 times greater than Earth's surface.  The 
bulk of Jupiter rotates once in 9 hours and 56 minutes, although 
the period determined by watching cloud features differs by up 
to five minutes due to intrinsic cloud motions.
 
	The visible "surface" of Jupiter is a deck of clouds of 
ammonia crystals, the tops of which occur at a level where the 
pressure is about half that at Earth's surface. The bulk of the 
atmosphere is made up of 89% molecular hydrogen (H2) and 11% helium 
(He). There are small amounts of gaseous ammonia (NH3), methane
(CH4), water (H2O), ethane (C2H6), acetylene (C2H2), carbon monoxide 
(CO), hydrogen cyanide (HCN), and even more exotic compounds such as 
phosphine (PH3) and germane (GeH4). At levels below the deck of 
ammonia clouds there are believed to be ammonium hydro-sulfide 
(NH4SH) clouds and water crystal (H2O) clouds, followed by clouds 
of liquid water. The visible clouds of Jupiter are very colorful.  
The cause of these colors is not yet known. "Contamination" by
various polymers of sulfur (S3, S4, S5, and S8), which are yellow, 
red, and brown, has been suggested as a possible cause of the riot 
of color, but in fact sulfur has not yet been detected spectroscop-
ically, and there are many other candidates as the source of the coloring.
 
	The meteorology of Jupiter is very complex and not well 
understood. Even in small telescopes, a series of parallel light 
bands called zones and darker bands called belts is quite obvious.  
The polar regions of the planet are dark.  Also present are light 
and dark ovals, the most famous of these being "the Great Red 
Spot." The Great Red Spot is larger than Earth, and although its 
color has brightened and faded, the spot has persisted for at least 
162.5 years, the earliest definite drawing of it being Schwabe's of 
5 September 1831. (There is less positive evidence that Hooke observed 
it as early as 1664.) It is thought that the brighter zones are cloud-
covered regions of upward moving atmosphere, while the belts are the 
regions of descending gases, the circulation driven by interior heat. 
The spots are thought to be large-scale vortices, much larger and
far more permanent than any terrestrial weather system.  
 
	The interior of Jupiter is totally unlike that of Earth. 
Earth has a solid crust "floating" on a denser mantle that is fluid 
on top and solid beneath, underlain by a fluid outer core that 
extends out to about half of Earth's radius and a solid inner core 
of about 1,220-km radius. The core is probably 75% iron, with the 
remainder nickel, perhaps silicon, and many different metals in 
small amounts. Jupiter on the other hand may well be fluid throughout, 
although it could have a "small" solid core (upwards of 15 Earth 
masses) of heavier elements such as iron and silicon extending out 
to perhaps 15% of its radius. The bulk of Jupiter is fluid hydrogen 
in two forms or phases, liquid molecular hydrogen on top and liquid 
metallic hydrogen below; the latter phase exists where the pressure 
is high enough, say 3-4 million atmospheres.  There could be a small 
layer of liquid helium below the hydrogen, separated out gravita-
tionally, and there is clearly some helium mixed in with the 
hydrogen.  The hydrogen is convecting heat (transporting heat by 
mass motion) from the interior, and that heat is easily detected 
by infrared measurements, since Jupiter radiates twice as much heat 
as it receives from the Sun.  The heat is generated largely by 
gravitational contraction and perhaps by gravitational separation 
of helium and other heavier elements from hydrogen, in other words, 
by the conversion of gravitational potential energy to thermal 
energy.  The moving metallic hydrogen in the interior is believed 
to be the source of Jupiter's strong magnetic field.
 
	Jupiter's magnetic field is much stronger than that of Earth.  
It is tipped about 11 degrees to Jupiter's rotational axis, similar 
to Earth's, but it is also offset from the center of Jupiter by about 
10,000 km. The magnetosphere of charged particles which it affects 
extends from 3.5 million to 7 million km in the direction toward the 
Sun, depending upon solar wind conditions, and at least 10 times that 
far in the anti-Sun direction.  The plasma trapped in this rotating, 
wobbling magnetosphere emits radio frequency radiation measurable 
from Earth at wavelengths from 1 m or less to as much as 30 km. The 
shorter waves are more or less continuously emitted, while at longer 
wavelengths the radiation is quite sporadic. Scientists will carefully 
monitor the Jovian magnetosphere to note the effect of the intrusion 
of large amounts of cometary dust into the Jovian magnetosphere.
 
	The two Voyager spacecraft discovered that Jupiter has faint 
dust rings extending out to about 53,000 km above the atmosphere.  
The brightest ring is the outermost, having only about 800-km width.  
Next inside comes a fainter ring about 5,000 km wide, while very 
tenuous dust extends down to the atmosphere.  Again, the effects of 
the intrusion of the dust from Shoemaker-Levy 9 will be interesting 
to see, though not easy to study from the ground.  
 
		  The Impact into Jupiter
 
	All 20-plus major impacts will occur at approximately the 
same position on Jupiter relative to the center of the planet, but 
because the planet is rotating the impacts will occur at different 
points in the atmosphere. The impacts will take place at approxi-
mately 45 degrees south latitude and 6.5 degrees of longitude from 
the limb, just out of view from Earth (approximately 15 degrees 
from the dawn terminator). Jupiter has a rotation period of 9.84 
hours, or a rotation rate of about 0.01 degrees/sec, so the impacts 
will occur on the farside of the planet but the point of impact in 
the atmosphere will rotate across the limb within about 11 minutes 
after the impact, and cross the dawn termninator within about 25 
minutes from the impact. From this point on the effects on the 
atmosphere should be observable from Earth, but the viewing of 
the atmosphere where the impact occurred will improve as the site 
rotates towards the center of the disk and we can see it face on.  
The comet particles will be moving almost exactly from (Jovian) 
south to north at the time of the impact, so they will strike the 
planet at an angle of 45 degrees to the surface. (The surface is 
defined for convenience as the Jovian cloud tops.) The impact 
velocity will be Jovian escape velocity, 60 km/sec.
 
	The times of collision of these fragments with Jupiter 
can only be currently estimated within about 20 minutes. As 
measurements of the orbit are made over the next few months 
the accuracy of these estimates should improve, so by 1 June 
the impact time will be known with an accuracy of about 16 minutes 
and by 1 July about 10 minutes. Eighteen hours before the first 
impact the uncertainty will be approximately 3 minutes. The 
relative positions of the fragments to each other are known much 
more accurately than the absolute position, so once the first 
fragment impacts Jupiter, the collision times of the remaining 
fragments will be better constrained.  The first fragment, A, 
will collide with Jupiter on 16 July at 19:11 Universal Time 
(UT).  Jupiter will be approximately 5.117 AU (~820 million km) 
from Earth, so the time for light to travel to the Earth will 
be about 43 minutes, and the collision will be observed on Earth 
at 19:54 UT (3:54 PM EDT) on 16 July. 
 
	For Earth-based observations, Jupiter will rise at about 
noon and set around midnight, so there will be a limited window 
to observe the collisions.  The head of the dust train around the 
fragments will reach Jupiter 1 to 2 months before the particles arrive.
 
	The predicted outcomes of the impacts with Jupiter span 
a large range.  This is due in part to the uncertainty in the 
size of the impacting bodies but even for a fixed size there is 
a wide range of predictions, largely because planetary scientists 
have never observed a collision of this magnitude.  It is not 
known what the effects of the impacts of the large fragments 
will be on Jupiter, the large mass (~10^12 to 10^14 kg) and high 
velocity (60 km/sec) guarantee highly energetic collisions.  
Various models of this collision have been hypothesized, and 
there is general agreement that a fragment will travel through 
the atmosphere to some depth and explode, creating a fireball 
which will rise back above the cloud tops. The explosion will 
also produce pressure waves in the atmosphere and "surface waves" 
at the cloud tops.  The rising material may consist of an equal 
amount of vaporized comet and Jovian atmosphere, but details about 
this, the depth of the explosion, the total amount of material 
ejected above the cloud tops, and almost all other effects of the 
impact are highly model dependent. Each impact (and the subsequent 
fall-back of ejected material over a period of ~3 hours after the 
collision will probably affect an area of the atmosphere from one 
to a few thousand km around the impact site. It will be difficult 
to see the objects within about 8 Jovian radii (~570,000 km).
 
	If the cometary nuclei have the sizes estimated from the 
observations with the Hubble Space Telescope and if they have the 
density of ice, each fragment will have a kinetic energy equivalent 
to roughly 10 million megatons of TNT (10^29 to 10^30 ergs).  The 
total energy of the collisions [of all fragments] may be as great 
as 100 million megatons of TNT; roughly 10,000 times the total 
destructive power of the world's nuclear arsen at the height of 
the Cold War.  The impacts will be as energetic as the collision 
of a large asteroid or comet with the Earth 65 million years ago.  
This latter cosmic catastrophe most probably led to the extinction 
of the dinosaurs and hundreds of other species at the geologic
Cretaceous-Tertiary (K-T) boundary layer.  
 
	The predictions of the effects differ in how they model 
the physical processes and there are significant uncertainties 
about which processes will dominate the interaction.  If ablation 
(melting and vaporization) and fragmentation dominate, the energy 
can be dissipated high in the atmosphere with very little material
penetrating far beneath the visible clouds.  If the shock wave in 
front of the fragment also confines the sides and causes the frag-
ment to behave like a fluid, then nuclei could penetrate far below 
the visible clouds.  Even in this case, there are disagreements about 
the depth to which the material will penetrate, with the largest 
estimates being several hundred kilometers below the cloudtops.
 
	The short-term effects at the atmospheric site of impact may 
be profound. Thermal plumes may rise to 700 km.  Whether permanent 
disturbances, such as a new Great Red Spot or White Ovals form, is 
also a subject of great debate.  The HST will monitor the atmosphere 
for changes in cloud morphology as each impact site rotates into view 
within a couple hours of the impact.
 
	In any case, there will be an optical flash lasting a 
few seconds as each nucleus passes through the stratosphere.  
The brightness of this flash will depend critically on the 
fraction of the energy which is released at these altitudes.  
If a large fragment penetrates below the cloudtops and releases 
much of its energy at large depths, then the initial optical 
flash will be faint but a buoyant hot plume will rise in the 
atmosphere like the fireball after a nuclear explosion, producing 
a second, longer flash lasting a minute or more and radiating 
most strongly in the infrared.  Although the impacts will occur 
on the far side of Jupiter, estimates show that the flashes may 
be bright enough to be observed from Earth in reflection off 
the inner satellites of Jupiter, particularly Io, if a satellite 
happens to be on the far side of Jupiter but still visible as 
seen from Earth.  The flashes will also be directly visible from 
the Galileo spacecraft.
 
	The shock waves produced by the impact onto Jupiter are 
predicted to penetrate into the interior of Jupiter, where they 
will be bent, much as the seismic waves from earthquakes are bent 
in passing through the interior of Earth.  These may lead to a prompt 
(within an hour or so) enhancement of the thermal emission over a 
very large circle centered on the impact.  Waves reflected from the 
density-discontinuities in the interior of Jupiter might also be
visible on the front side within an hour or two of the impact.  
Finally, the shock waves may initiate natural oscillations of Jupiter, 
similar to the ringing of a bell, although the predictions disagree 
on whether these oscillations will be strong enough to observe with 
the instrumentation currently available.  Observation of any of 
these phenomena can provide a unique probe of the interior structure 
of Jupiter, for which we now have only theoretical models with almost 
no observational data.
 
	The plume of material that would be brought up from Jupiter's 
troposphere (below the clouds) will bring up much material from the 
comet as well as material from the atmosphere itself.  Much of the 
material will be dissociated and even ionized but the composition of 
this material can give us clues to the chemical composition of the 
atmosphere below the clouds.  It is also widely thought that as the 
material recombines, some species, notably water, will condense and 
form clouds in the stratosphere.  The spreading of these clouds in 
latitude and longitude can tell us about the circulation in the 
stratosphere and the altitude at which the clouds form can tell us 
about the composition of the material brought up from below.  The 
grains of the comet which impact Jupiter over a period of several 
months may form a thin haze which will also circulate through the 
atmosphere.  Enough clouds might form high in the stratosphere to 
obscure the clouds at lower altitudes that are normally seen from Earth.
 
	Interactions of cometary material with Jupiter's magnetic 
field have been predicted to lead to observable effects on Jupiter's 
radio emission, injection of material into Jupiter's auroral zone, 
and disruption of the ring of grains that now encircles Jupiter.
 
	Somewhat less certainly the material may cause observable 
changes in the torus of plasma that circles Jupiter in association 
with the orbit of Io or may release gas in the outer magnetosphere 
of Jupiter.  It has also been predicted that the cometary material 
may, after ten years, form a new ring about Jupiter although there 
are some doubts whether this will happen.
 
	Overview of the Hubble Space Telescope
 
	The Hubble Space Telescope is a coooperative program of 
the European Space Agency (ESA) and the National Aeronautics and 
Space Administration (NASA) to operate a long-lived space-based 
observatory for the benefit of the international astronomical 
community.  HST is an observatory first dreamt of in the 1940s, 
designed and built in the 1970s and 80s, and operational only in 
the 1990s.  Since its preliminary inception, HST was designed to 
be a different type of mission for NASA -- a permanent space-based 
observatory.  To accomplish this goal and protect the spacecraft 
against instrument and equipment failures, NASA had always planned 
on regular servicing missions.  Hubble has special grapple
fixtures, 76 handholds, and stabilized in all three axes.
 
	When originally planned in 1979, the Large Space Telescope 
program called for return to Earth, refurbishment, and relaunch 
every 5 years, with on-orbit servicing every 2.5 years.  Hardware 
lifetime and reliability requirements were based on that 2.5-year 
interval between servicing missions.  In 1985, contamination and 
structural loading concerns associated with return to Earth aboard 
the shuttle eliminated the concept of ground return from the program.  
NASA decided that on-orbit servicing might be adequate to maintain 
HST for its 15-year design life.  A three year cycle of on-orbit 
servicing was adopted.  The first HST servicing mission in December 
1993 was an enormous success.  Future servicing missions are tenta-
tively planned for March 1997, mid-1999, and mid-2002.  Contingency 
flights could still be added to the shuttle manifest to perform 
specific tasks that cannot wait for the next regularly scheduled 
servicing mission (and/or required tasks that were not completed 
on a given servicing mission).
 
	The four years since the launch of HST in 1990 have been 
momentous, with the discovery of spherical aberration and the 
search for a practical solution.  The STS-61 (Endeavour) mission 
of December 1993 fully obviated the effects of spherical aberration 
and fully restored the functionality of HST.
 
		The Science Instruments
 
Wide Field/Planetary Camera 2
 
	The original Wide Field/Planetary Camera (WF/PC1) was 
changed out and displaced by WF/PC2 on the STS-61 shuttle mission 
in December 1993.  WF/PC2 was a spare instrument developed in 1985 
by the Jet Propulsion Laboratory in Pasadena, California.
 
	WF/PC2 is actually four cameras.  The relay mirrors in 
WF/PC2 are spherically aberrated to correct for the spherically 
aberrated primary mirror of the observatory.  (HST's primary mirror 
is 2 microns too flat at the edge, so the corrective optics within 
WF/PC2 are too high by that same amount.)
 
	The "heart" of WF/PC2 consists of an L-shaped trio of 
wide-field sensors and a smaller, high resolution ("planetary") 
camera tucked in the square's remaining corner. 
 
	WF/PC2 has been used to image P/SL9 and will be used 
extensively to "map" Jupiter's features before, during, and after 
the collision events.
 
Corrective Optics Space Telescope Axial Replacement
 
	COSTAR is not a science instrument; it is a corrective 
optics package that displaced the High Speed Photometer during the 
first servicing mission to HST.  COSTAR is designed to optically 
correct the effects of the primary mirror's aberration on the three 
remaining scientific instruments:  Faint Object Camera (FOC), Faint 
Object Spectrograph (FOS), and the Goddard High Resolution Spectrograph 
(GHRS).
 
Faint Object Camera
 
	The Faint Object Camera is built by the European Space 
Agency.  It is the only instrument to utilize the full spatial 
resolving power of HST.
 
	There are two complete detector system of the FOC.  Each 
uses an image intensifier tube to produce an image on a phosphor 
screen that is 100,000 times brighter than the light received.  
This phosphor image is then scanned by a sensitive electron-bombarded 
silicon (EBS) television camera.  This system is so sensitive that 
objects brighter than 21st magnitude must be dimmed by the camera's 
filter systems to avoid saturating the detectors.  Even with a broad-
band filter, the brightest object which can be accurately measured 
is 20th magnitude.
 
	The FOC offers three different focal ratios: f/48, f/96, 
and f/288 on a standard television picture format.  The f/48 image 
measures 22 X 22 arc-seconds and yields resolution (pixel size) of 
0.043 arc-seconds.  The f/96 mode provides an image of 11 X 11 arc-
seconds on each side and a resolution of 0.022 arc-seconds.  The f/288 
field of view is 3.6 X 3.6 arc-seconds square, with resolution down to
0.0072 arc-seconds.
 
Faint Object Spectrograph
 
	A spectrograph spreads out the light gathered by a telescope 
so that it can be analyzed to determine such properties of celestial 
objects as chemical composition and abundances, temperature, radial 
velocity, rotational velocity, and magnetic fields. The Faint Object 
Spectrograph (FOS) exmaines fainter objects than the HRS, and can 
study these objects across a much wider spectral range from the UV 
(1150 A) through the visible red and the near-IR (8000 A).
 
	The FOS uses two 512-element Digicon sensors (light 
intensifiers) to light.  The "blue" tube is sensitive from 1150 to 
5500 A (UV to yellow).  The "red" tube is sensitive from 1800 to 
8000 A (longer UV through red).  Light can enter the FOS through any 
of 11 different apertures from 0.1 to about 1.0 arc-seconds in diameter.  
There are also two occulting devices to block out light from the center 
of an object while allowing the light from just outside the center to 
pass on through. This could allow analysis of the shells of gas around 
red giant stars of the faint galaxies around a quasar.
 
	The FOS has two modes of operation:  low resolution and high 
resolution.  At low resolution, it can reach 26th magnitude in one hour 
with a resolving power of 250.  At high resolution, the FOS can reach 
only 22nd magnitude in an hour (before S/N becomes a problem), but the 
resolving power is increased to 1300.
 
Goddard High Resolution Spectrograph
 
	The High Resolution Spectrograph also separates incoming 
light into its spectral components so that the composition, temperature, 
motion, and other chemical and physical properties of the objects can be 
analyzed.  The HRS contrasts with the FOS in that it concentrates entirely 
on UV spectroscopy and trades the extremely faint objects for the ability 
to analyze very fine spectral detail.  Like the FOS, the HRS uses two 
521-channel Digicon electronic light detectors, but the detectors of the 
HRS are deliberately blind to visible light. One tube is sensitive from 
1050 to 1700 A; while the other is sensitive from 1150 to 3200 A.
 
	The HRS also has three resolution modes:  low, medium, and high.  
"Low resolution" for the HRS is 2000 A higher than the best resolution 
available on the FOS.  Examining a feature at 1200 A, the HRS can resolve 
detail of 0.6 A and can examine objects down to 19th magnitude.  At medium 
resolution of 20,000; that same spectral feature at 1200 A can be seen in 
detail down to 0.06 A, but the object must be brighter than 16th magnitude 
to be studied.  High resolution for the HRS is 100,000; allowing a spectral 
line at 1200 A to be resolved down to 0.012 A.  However, "high resolution" 
can be applied only to objects of 14th magnitude or brighter.  The HRS can 
also discriminate between variation in light from ojbects as rapid as 
100 milliseconds apart.
 
		Mission Operations and Observations
 
	Although HST operates around the clock, not all of its time 
is spent observing.  Each orbit lasts about 95 minutes, with time 
allocated for housekeepingfunctions and for observations.  "Housekeeping" 
functions includes turning the telescope to acquire a new target, or 
avoid the Sun or Moon, switching communications antennas and data 
transmission modes, receiving command loads and downlinking data, 
calibrating and similar activities.
 
	When STScI completes its master observing plan, the schedule 
is forwarded to Goddard's Space Telescope Operations Control Center 
(STOCC), where the science and housekeeping plans are merged into a 
detailed operations schedule.  Each event is translated into a series 
of commands to be sent to the onboard computers.  Computer loads are 
uplinked several times a day to keep the telescope operating efficiently.
 
	When possible two scientific instruments are used simul-
taneously to observe adjacent target regions of the sky.  For example, 
while a spectrograph is focused on a chosen star or nebula, the WF/PC 
can image a sky region offset slightly from the main viewing target.  
During observations the Fine Guidance Sensors (FGS) track their re-
spective guide stars to keep the telescope pointed steadily at the 
right target.
 
	In an astronomer desires to be present during the observation, 
there is a console at STScI and another at the STOCC, where monitors 
display images or other data as the observations occurs.  Some limited 
real-time commanding for target acquisition or filter changing is per-
formed at these stations, if the observation program has been set up 
to allow for it, but spontaneous control is not possible.
 
	Engineering and scientific data from HST, as well as uplinked 
operational commands, are transmitted through the Tracking Data Relay 
Satellite (TDRS) system and its companion ground station at White Sands, 
New Mexico.  Up to 24 hours of commands can be stored in the onboard 
computers.  Data can be broadcast from HST to the ground stations 
immediately or stored on tape and downlinked later.
 
	The observer on the ground can examine the "raw" images 
and other data within a few minutes for a quick-look analysis.  
Within 24 hours, GSFC formats the data for delivery to the STScI.  
STScI is responsible for data processing (calibration, editing, 
distribution, and maintenance of the data for the scientific community).
 
	Competition is keen for HST observing time.  Only one of 
every ten proposals is accepted.  This unique space-based observatory 
is operated as an international research center; as a resource for 
astronomers world-wide.  
 
	The Hubble Space Telescope is the unique instrument of 
choice for the upcoming collision of Comet Shoemaker-Levy 9 into 
Jupiter.  The data gleaned from this momentous event will be 
invaluable for decades to come.
 
	       Other Spacecraft
 
Galileo
 
	Galileo is enroute to Jupiter and will be about 1.5 
AU (230 million km) from Jupiter at the time of the impact.  
At this range, Jupiter will be ~60 pixels across in the solid 
state imaging camera, a resolution of ~2400 km/pixel.  Galileo 
will have a direct view of the impact sites, with an elevation 
of approximately 23 degrees above the horizon as seen from the 
impact point.  The unavailability of the main antenna, forcing 
use of the low-gain antenna for data transmission, severely limits 
the imaging options available to Galileo. The low-gain antenna 
will be able to transmit to Earth at 10 bits/sec, so real-time 
transmission of imaging will not be possible.  The Galileo tape 
recorder can store ~125 full-frame equivalents. On-board data 
compression and mosaicking may allow up to 64 images per frame 
to be stored, but playback of the recorded images must be com-
pleted by January, 1995 when Galileo reaches Jupiter.  This will 
only allow transmission of ~5 full-frame equivalents, or approxi-
mately 320 images.  There will be the capability for limited 
on-board editing and the images can be chosen after the impacts 
have occured, so the impact timing will be well known, but the 
imaging times must be scheduled weeks before the impacts.  Each 
image requires 2.33 seconds, so a full frame of 64 images will 
cover ~2.5 minutes, and consist of ~2400 kilobits. A new mosaic 
can be started in ~6 seconds.  The camera has a number of filters 
from violet through near-IR and requires 5 to 10 seconds to change 
filters. In addition to imaging data, Galileo has a high time 
resolution photopolarimeter radiometer, near-infrared mapping 
spectrometer, radio reciever, and ultraviolet spectrometer which 
can be used to study the collisions. The limited storage capacity 
and low transmission rate of Galileo make the timing of all the 
impact observations critical. 
 
Ulysses
 
	The Ulysses spacecraft is in a high inclination orbit 
relative to the ecliptic plane, which will carry it under the 
south pole of the Sun in September 1994.  Its payload includes 
sensitive radio receivers that may be able to observe both the 
immediate consequences of the collisions of Comet Shoemaker-Levy 
9 fragments with Jupiter and the long-term effects on the Jovian 
magnetosphere.
 
	Ulysses will be 2.5 AU (375 million km) south of Jupiter 
at the time of impact and will also have a direct line of sight 
to the impact point. From this position the Ulysses unified radio 
and plasma wave (URAP) experiment will monitor radio emissions 
between 1 and 940 KHz, sweeping through the spectrum approximately 
every 2 minutes. URAP will be able to detect radio emissions down
to 10^14 ergs.  There are no imaging experiments on Ulysses.
 
Voyager 2
 
	Voyager 2 is on it's way out of the solar system, 44 AU 
from Jupiter at the time of the impact. The planetary radio 
astronomy (PRA) experiment will be monitoring radio emissions 
in the 1 KHz to 390 KHz range with a detection limit of 10^19 
to 10^20 ergs.  PRA will sweep through this spectrum every 96 
seconds.  The Voyager 2 imaging system will not be used.
 
International Ultraviolet Explorer
 
	The International Ultraviolet Explorer (IUE) satellite 
will be devoting 55 eight-hour shifts (approximately 2-1/2 weeks 
total) of ultraviolet (UV) spectroscopic observations to the Comet 
Shoemaker-Levy 9 impact events, with 30 shifts allotted to the 
American effort (Principal Investigators:  Walt Harris, University 
of Michigan; Tim Livengood, Goddard Space Flight Center; Melissa
McGrath, Space Telescope Science Institute) and 25 shifts allotted 
to the European effort (PIs: Renee Prange, Institute d'Astrophysique 
Spatiale; Michel Festou, Observatoire Midi-Pyrenees).  The observing 
campaign will begin with baseline observations in mid-June, and continue 
through mid-August.  During the week of the actual impacts,  IUE will 
be observing the Jovian system continuously.
 
	The IUE campaign will be devoted to in-depth studies of 
the Jovian aurorae, the Jovian Lyman-alpha bulge, the chemical 
composition and structure of the upper atmosphere, and the Io torus.  
The IUE observations will provide a comprehensive study of the physics 
of the cometary impact into the Jovian atmosphere, which can provide 
new insights into Jupiter's atmospheric structure, composition, and
chemistry, constrain global diffusion processes and timescales in 
the upper atmosphere, characterize the response of the Lyman-alpha 
bulge to the impacting fragments and associated dust, study the 
atmospheric modification of the aurora by the impact material deposited 
by the comet and by the material ejected into the magnetosphere from 
the deep atmosphere, and investigate the mass loading processes in 
the magnetosphere.     
 
Ground-Based
 
	Many large telescopes will be available on Earth with 
which to observe the phenomena associated with the Shoemaker-Levy 
9 impacts on Jupiter in visible, infrared, and radio wavelengths.  
Small portable telescopes can fill in gaps in existing observatory 
locations for some purposes. Imaging, photometry, spectroscopy, and 
radiometry will certainly be carried out using a multitude of 
detectors. Many of these attempts will fail, but some should 
succeed.  Apart from the obvious difficulty that the impacts will 
occur on the back side of Jupiter as seen from Earth, the biggest 
problem is that Jupiter in July can only be observed usefully for 
about two hours per night from any given site.  Earlier the sky 
is still too bright and later the planet is too close to the 
horizon. Therefore, to keep Jupiter under continuous surveillance 
would require a dozen observatories equally spaced in longitude 
clear around the globe.  A dozen observatories is feasible, but 
equal spacing is not. There will be gaps in the coverage, notably 
in the Pacific Ocean, where Mauna Kea, Hawaii, is the only 
astronomical bastion. 
 
		The Kuiper Airborne Observatory (KAO)
 
	The KAO is a modified C-141 aircraft with a 36-inch (0.9 
meter) telescope mounted in it.  The telescope looks out the left 
side of the airplane through an open hole in the fuselage.  No window 
is used because a window would increase the infrared background level.  
The telescope is stabilized by: 1) a vibration isolation system (shock 
absorbers); 2) a spherical air bearing; 3) a gyroscope controlled 
pointing system; and 4) an optical tracking system.  The telescope
can point to a couple of arc-seconds even in moderate turbulence.
 
	The airplane typically flies at 41,000 feet (12.5 km), 
above the Earth's tropopause.  The temperature is very cold there, 
about -50 degrees Celsius, so water vapor is largely frozen out.  
There is about 10 precipitable microns of water in the atmospheric 
column above the KAO (about the same amount as in the atmosphere of 
Mars).  This allows the KAO to observe most of the infrared wavelengths 
that are obscured by atmospheric absorption at ground-based sites.
Flights are normally 7.5 hours long, but the aircraft has flown 
observing missions as long as 10 hours.  The comet impact flights 
are all around 9.5 hours to maximize the observing time on Jupiter 
after each impact.  Because these observations will be made in the 
infrared and the infrared sky is about as dark in the daytime as it 
is at night, we will be able to observe in the afternoon and into 
the evening.
 
	The main advantage that the airborne observatory brings 
to bear is its ability to observe water with minimal contamination 
by terrestrial water vapor.  The observing projects focus on 
observing tropospheric water (within Jupiter's cloud deck) brought 
up by the comet impact, or possibly on water in the comet if it breaks 
up above Jupiter's tropopause.  The KAO team will also look for 
other compounds that would be unobservable from the ground due 
to terrestrial atmospheric absorption.  
 
	The KAO will be deployed to Australia to maximize the 
number of times the immediate aftermath of an impact can be observed.  
The available integration time on each flight will be typically 4-5 
hours, from impact time to substantially after the central meridian 
crossing of the impact point.  The KAO will leave NASA Ames on 12 July, 
return on 6 August.  The last part of the deployment will be devoted 
to observations of southern hemisphere objects as part of the regular 
airborne astronomy program.
 
		HST Science Observation Teams
 
HST Investigation of Comet P/Shoemaker-Levy 9
 
	Comet P/Shoemaker-Levy 9 is being studied intensively by 
HST prior to the impacts. In an investigation being led by Harold 
A. Weaver (STScI), 40 orbits of HST time are being used to perform 
imaging and spectroscopic observations of the comet during the 
period from late January 1994 until the final hours before the 
fragments make their fiery plunge into Jupiter's atmosphere during 
mid-July. In addition, 4 orbits of time were awarded to a team 
led by Terrence Rettig (University of Notre Dame) for further 
detailed imaging of the comet.
 
	The most important scientific objectives of the cometary 
investigations are: (1) determine whether or not there are large, 
solid nuclei at the condensation points in the comet and estimate 
their sizes, (2) examine carefully the near-nucleus morphology of 
the brightest objects to search for further fragmentation and out-
gassing activity, (3) monitor the temporal variability of the 
largest nuclei, and (4) take deep spectroscopic exposures to search 
for atoms and molecules in the vicinity of the comet.
 
	Since the energy deposited into the Jovian atmosphere is 
proportional to the cube of the size of the impacting object, 
accurate nuclear sizes must be determined before accurate predictions 
of impact phenomena can be made.  HST's high spatial resolution 
provides higher contrast between each nucleus and its surrounding 
coma than can be achieved with any other optical telescope. Even in 
the HST case the observed intensity is primarily due to light scattered 
from the coma, but the improved contrast in the HST images allows for 
a more accurate determination of the nuclear magnitudes, from which 
sizes can be estimated.
 
	The July 1993 HST images of P/Shoemaker-Levy 9 reveal a complex 
morphology around each nucleus. At least several nuclei that seem to 
be single objects at ground-based resolution emerge as multiple objects 
at HST's resolution.  Were these neighbors produced during the breakup 
of the P/SL9's parent body, or has there been continuing fragmentation 
in the ensuing period?  One of the most intriguing results from the 
currently available HST data is the possibility that the nuclei are 
continuing to fragment. By careful examination of the HST images near 
the brighter nuclei, and particularly by searching for temporal varia-
bility in the image morphology, we can detect fragmentation and "con-
ventional" cometary activity. Any evidence for fragmentation will provide 
important information on the strength of the nuclei.  Cometary nuclei are 
known to be extremely fragile and often breakup for no apparent reason 
(i.e., many nuclei split without being near any massive perturber).  
Thus, we might expect to see continuing fragmentation of nuclei in 
this comet well outside the Roche limit of Jupiter.  At large 
distances from Jupiter, the splitting of nuclei could be induced 
by nuclear rotation, cometary activity (e.g., amorphous-to-crystalline 
ice transitions, which has been proposed as the source of coma 
activity in P/Schwassmann-Wachmann 1), or a combination of both.
 
	Our spectroscopic program consists of two relatively deep 
exposures near the brightest nucleus in order to search for atomic 
and molecular emissions. Using the G270H grating of the Faint Object 
Spectrograph (FOS) these observations cover the wavelength range 
from 2223 to 3278 Angstroms. The new observations should be at least 
three times more sensitive than previous HST observations.  Besides 
covering the strong hydroxyl (OH) bands, our spectrum will serendipi-
tously cover a strong emission band of singly ionized carbon dioxide 
(CO2+) and resonance transitions of several metals (i.e., Mg I, 
Mg II, and Si I).
 
Spectroscopy
 
	The Jupiter spectroscopy team headed by Keith Noll 
(STScI) will search for molecular remnants of the comet and 
fireball in Jupiter's upper atmosphere.  The team consists of 
seven investigators:  Noll (STScI), Melissa McGrath (STScI),
Larry Trafton (University of Texas),  Hal Weaver (STScI),  
John Caldwell (York University), Roger Yelle (University of 
Arizona),  and S. Atreya (University of Michigan).
 
	Even though the comet's mass is dwarfed by the mass of 
Jupiter, the impact can cause local disturbances to the 
composition of the atmosphere that could be detectable with HST.  
The two spectrometers on HST, the Faint Object Spectrograph (FOS) 
and the Goddard High Resolution Spectrograph (HRS), will be used 
to search for the spectral fingerprints of unusual molecules near 
the site of one of the large impacts.
 
	Jupiter's stratosphere will be subject to two sources 
of foreign material, the comet itself, and gas from deep below 
Jupiter's cloudtops.  There are large uncertainties in the pre-
dictions of how deep the comet fragments will penetrate into 
Jupiter's atmosphere before they are disrupted.  But, if they 
do penetrate below Jupiter's clouds as predicted by some, a 
large volume of heated gas could rise into Jupiter's stratosphere.  
As on the Earth, Jupiter's stratosphere is lacking in the gases 
that condense out at lower altitudes.  The sudden introduction 
of gas containing some of these condensible molecules can be 
likened to what happens on Earth when a volcano such as Pinatubo 
injects large amounts of gas and dust into the stratosphere.  
Once in this stable portion of the atmosphere on either planet, 
the unusual material can linger for years.
 
	The spectroscopic investigation will consist of 12 orbits
spread over three complementary programs.  Several of the observations 
will be done within the first few days after the impact of fragment 
G on 18 July at 07:35 UTC.  The team also wants to study how the 
atmosphere evolves so some observations will continue into late August.
 
	The FOS will obtain broad-coverage spectra from ~1750 - 
3300 A. Quite a few atmospheric molecules have absorptions in this 
interval, particularly below 2000 A.  One molecule that we will look 
for with special interest is hydrogen sulfide (H2S), a possible ingredient 
for the still-unidentified coloring agent in Jupiter's clouds.
 
	The spectroscopy team will focus in on two spectral 
intervals with the HRS. In one experiment, the team will search 
for silicon oxide (SiO) which should be produced from the rocky 
material in the cometary nucleus.  The usefulness of this  
molecule is the fact that it can come only from the comet 
since any silicon in Jupiter's atmosphere resides far below 
the deepest possible penetration of the fragments.  Measuring 
this will help sort out the relative contributions of the comet 
and Jupiter's deep atmosphere to the disturbed region of the 
stratosphere.  Finally, the spectroscopy team will use the HRS 
to search for carbon monoxide (CO) and other possible emissions 
near 1500 A.  CO is an indicator of the amount of oxygen intro-
duced into the normally oxygen-free stratosphere.  Any results 
obtained with the HRS will be combined with ground-based observa-
tions of CO at infrared wavelengths sensitive to deeper layers to 
reconstruct the variation of CO with altitude.
 
Atmospheric Dynamics
 
	The HST Jupiter atmospheric dynamics team, led by Heidi 
Hammel (Massachusetts Institute of Technology), will be carefully 
monitoring Jupiter to observe how its atmosphere reacts to incoming 
cometary nuclei.  The atmospheric dynamics team consists of five 
investigators:  Hammel (MIT),  Reta Beebe (New Mexico State 
University), Andrew Ingersoll (California Institute of Technology), 
Bob West (JPL), and Glenn Orton (JPL/Caltech).
 
	Researchers at the Massachusetts Institute of Technology 
have conducted computer simulations of the collisions' effect on 
Jupiter's weather.  These simulations show waves travelling outward 
from the impact sites and propagating around the planet in the days 
following each impact.  The predicted "inertia-gravity" waves are on 
Jupiter's "surface" (atmosphere) may emanate from the impact sites and 
would be analagous to the ripples from dropping a pebble in a pond.  
 
	Some theorists believe that the waves will be "seismic" 
in nature, with the atmosphere of Jupiter ringing like a bell.  
Such phenomenon may occur within the first hours after an impact.  
These seismic waves would travel much faster than the inertia-gravity 
waves, and quite likely more difficult to detect. 
 
	Using HST, Hammel's team hopes to detect and observe the 
inertia-gravity waves which may take hours to days.  The temperature 
deviation in such a typical wave may be as much as 0.1 to 1 deg Celsius; 
quite possibly visible from Earth in the best telescopic views.
 
	The speed at which these waves travel depends on their 
depth in the atmosphere and on stability parameters that are only 
poorly known.   While Hammel's team will observe the impact and its 
aftermath with the Hubble Space Telescope, a team of scientists
will utilize the NASA Infrared Telescope Facility (IRTF) on Mauna 
Kea, Hawaii.  The IRTF and HST groups hope to measure wave speeds 
and thus determine the Jovian atmospheric parameters more accurately.  
Better-known parameters will, in turn, improve understanding of 
planetary weather systems.
 
	Another exciting possibility is that new cloud features 
may form at the impact locations.  These clouds might then be 
trapped by surrounding high-speed jets and spun up into vortices 
that might last for days or weeks.   
 
	Finally,  cometary material will impact Jupiter's upper 
atmosphere.  This material (ices and dust) could significantly 
alter the reflectivity of the atmosphere, and could linger for 
weeks or months.   The goal of Hammel's HST observing plan is to 
observe all of these phenomena, while simultaneously and compre-
hensively mapping of Jupiter's atmosphere.  
 
	The primary "products" will be multicolor WF/PC "maps" 
(images) of Jupiter.  These new WF/PC2 maps will be compared 
against the latest Jupiter images with older, WF/PC1 images, 
as well as Voyager spacecraft images of Jupiter.  At the very 
least,  an exquisite time-lapse series of the best images of 
Jupiter ever acquired by ground-based astronomy and spacecraft 
will be obtained.
 
 
Cometary Particles and Aerosols in Jupiter's Stratosphere
 
	The search for cometary particles in Jupiter's stratosphere 
is led by Robert West of the Jet Propulsion Laboratory (JPL).  
West's team will image Jupiter in the ultraviolet and near-IR 
methane band filters to observe these particles as tracers of 
Jupiter's stratospheric winds.  West's co-investigators include 
A. James Friedson (JPL), Erich Karkoschka (Lunar and Planetary 
Laboratory, University of Arizona), and Kevin Baines (JPL). 
 
	The impact on Jupiter of fragments of P/Shoemaker-Levy 9 
will provide an unprecedented opportunity to study the dynamics, 
chemistry, and aerosol microphysics of Jupiter's stratosphere.
Understanding the dynamics of the stratospheres of most planets is
difficult because there are usually no markers to track winds (the
clouds we normally see on Jupiter are deeper, in the troposphere).  
For the first time, we expect to see localized stratospheric tracer 
particles in Jupiter's atmosphere from directly deposited cometary
grains and from condensable gases exhumed from the deeper atmosphere.
 
	Dust and small pieces of the comet will be deposited directly 
into the stratosphere on a global scale, while the largest fragments 
will enter near latitude 40 degrees South.  Some calculations predict 
the large impactors will penetrate into the troposphere, below the 
visible clouds and create a fireball which will rebound to the top 
of the atmosphere.  The fireball carries with it Jovian air from 
below the cloudtops.  This deeper gas contains a good deal more of 
condensible volatiles like water (H20), ammonia (NH3), and hydrogen 
sulfide (H2S) than is usual in the cold upper atmosphere.  This 
material is ejected over a region a few thousand kilometers in 
radius.  From that localized region, the Jovian stratospheric winds
will distribute this material globally.
 
	An analogous situation occurs in Earth's atmosphere when 
large volcanic eruptions like El Chichon and Pinatubo inject obser-
vable particles into the stratosphere.  From observations of the number 
and size of small particles as a function of altitude, latitude, and 
time, we are able to study meridional (north-south, and vertical) 
circulation, planetary-scale waves and other dynamical processes by 
their effects on the spreading of the haze particles.
 
	In the search for the P/SL9 particles in Jupiter's strato-
sphere, West's team will use a powerful combination of UV and near-IR 
methane-band filters available with the WF/PC2 to observe the newly 
created stratospheric haze on Jupiter.  The signature of aerosols 
is strongest at these wavelengths.  Further, the UV observations 
are important in understanding any changes in stratospheric solar 
heating which may occur as a result of the additional aerosol burden, 
and which would perturb the stratospheric circulation.
 
Jupiter's Upper Atmosphere
 
	The HST Jupiter upper atmosphere imaging team, led by 
John T. Clarke (University of Michigan), will image Jupiter at 
far-ultraviolet wavelengths to observe the polar aurora as a 
tracer of magnetospheric activity, search for lower latitude 
auroral emission "arcs" associated with the passage of the comet 
fragments through Jupiter's magnetic field, and look for the 
signature of the comet fragment impact sites in the sunlight 
reflected from Jupiter's upper atmosphere.  The upper atmosphere 
imaging team consists of Clarke, Renee Prange (Institute 
d'Astrophysique Spataile, Orsay, France), and 17 co-investigators 
from the US and Europe.
 
	As the comet fragments approach Jupiter, they will be 
depositing trails of material in Jupiter's magnetosphere as they 
move at high speeds through the Jovian magnetic field.  The amount 
of material they contribute is expected to be small compared with 
the natural supply from the satellite Io, however the new material 
may alter the normal distribution or motions of the charged particles 
in Jupiter's magnetosphere.  The upper atmosphere imaging team will 
look for such changes by observing Jupiter's aurora, or "northern 
lights," which are produced by the impact of these magnetospheric 
charged particles with Jupiter's upper atmosphere near the magnetic 
poles.  In addition, the relative motion of the comet fragments with 
respect to Jupiter's magnetic field could generate electrical currents 
which pass through Jupiter's upper atmosphere at lower latitudes than 
the normal auroral emissions.  The team will attempt to observe these 
low latitude auroral "arcs".
 
	There is a large uncertainty in our knowledge of the mass 
and stability of the comet fragments, and therefore in our knowledge 
of the depth into Jupiter's atmosphere that they will penetrate.  
If the fragments are small or held together weakly, they will be 
vaporized by atmospheric friction in Jupiter's upper atmosphere, 
and the cometary material will be deposited into the upper atmosphere 
several hundred kilometers above the visible cloud tops.  This part 
of Jupiter's upper atmosphere can be observed by far-ultraviolet 
(far-UV) sunlight reflected by the atmosphere's primary constituent 
H2, and also absorbed by other species.  The added material in Jupiter's 
upper atmosphere may appear as dark regions in the far-UV images 
both from absorption by gas from the comet fragments and also lower 
atmospheric gas that convectively rises into the upper atmosphere 
from the heat of the impact.  If these far-UV dark regions are detected, 
we will also see how they drift horizontally with time, and may for the 
first time be able to measure the speed and direction of the winds in 
Jupiter's upper atmosphere.
 
	Far-UV wavelengths of light (below 2000 Angstroms) are 
strongly absorbed by atmospheric gases, and it is necessary to 
place an instrument above the Earth's atmosphere to take images 
of celestial objects at these wavelengths.  The planets also appear 
very different in the far-UV.  For example, far-UV images of the 
Earth from space show sunlight reflected from the upper atmosphere 
(altitudes above 100 km) and also bright emissions from the polar 
aurora and from diffuse airglow, which is emission from the upper 
atmosphere produced by a combination of fluorescence of far-UV 
sunlight and charged particle collisions with atmospheric gases.  
The emissions provide information about the interaction of the 
upper atmosphere with charged particles in the planet's magnetic 
field, and the reflected far-UV sunlight gives information about 
the altitude and spatial distribution of molecules in the upper 
atmosphere that absorb far-UV sunlight.  Far-UV images in general 
give information about the highest regions of a planet's atmosphere 
which interact with the space environment.  The far-UV emissions 
observed from Jupiter are similar to those from the Earth, although 
Jupiter's aurora (or northern and southern lights) are more than 
1000 times more energetic than the Earth's.  Far-UV images of Jupiter 
will be taken while the comet trail and dust clouds are in Jupiter's 
magnetic field, both before and after the impacts of the comet 
fragments.  
 
Comet Shoemaker-Levy 9's Impact on the Io Torus
 
	The Io torus is a donut-shaped region filled with sulfur, 
oxygen and electrons that surrounds Jupiter at the orbit of its moon 
Io, about 400,000 km from the planet.  It is maintained by Jupiter's 
magnetic field, which is about 10 times stronger than the magnetic 
field at the Earth's surface. This donut of material is an indirect 
result of Io's active volcanoes.  A program to study this region for 
evidence of the comet fragments and their associated dust will be 
conducted by a team of seven investigators led by Melissa A. McGrath 
(Space Telescope Science Institute) using two instruments aboard the 
Hubble Space Telescope, the GHRS and the FOS.  The presence of the 
comet fragments and their associated dust near Jupiter may release 
new material, in particular silicon and carbon, into the Io torus that 
is not normally present, or may disrupt the normally prodigious UV
emissions from this structure.  The Hubble investigation will search 
for evidence of any new elements in the torus, as well as carefully 
measure the brightness of the normal ultraviolet emissions, for evidence 
of the comet passage.
 
							ATTACHMENT A
 
The timeline below contains the most up-to-date information
RE: the HST Jupiter campaign's mission timeline and predicted
impact times of each P/SL9 fragment [based on Chodas, Yeomans,
et al.].
 
(1)  HST orbit since January's SOT meeting
 
Using the most recent HST ephemeris supplied by Dave Taylor (SPSS),
all orbit visibility periods occur approximately 7 minutes earlier
(than based upon the information available at the SOT meeting).  This
"slip" does not affect the currently planned science for the Jupiter
campaign.
 
However, the following orbits graze SAA contour 5 (this was not known
at the time of the January SOT meeting):
 
	orbit  87  202:06:02 -- 3 min	 Hammel WFPC
	      102  203:06:09 -- 2 min    Hammel WFPC
	      117  203:06:17 -- 1 min    Hammel WFPC
   
 
(2) Delta_t_tot Changes for Impact Times (since Jan. SOT mtg.)
 
 
 
			         Delta_t_tot
			         (chg. from
EVENT	DATE	Time (UTC)	 Jan. SOT mtg.)
 
===================================================================
 
A=21	16 Jul	19:54		+18 minutes
 
B=20	17 Jul	02:49           +11 minutes
 
C=19	  "	06:56		+26 minutes
 
D=18	  "	11:42		+11 minutes 
 
E=17	  "	15:03		+25 minutes
 
F=16	18 Jul	00:28		+14 minutes
 
G=15	  "	07:28		+30 minutes
 
H=14	  "	19:26		+28 minutes
 
K=12	19 Jul	10:18		+28 minutes
 
L=11	  "	22:07		+09 minutes 
 
N=9	20 Jul	10:19		+29 minutes
 
P2=8b	  "	15:05		+12 minutes
 
Q2=7b	  "	19:32           +48 minutes 
Q1=7a	  "	19:59		+1 hr 16 min 
 
R=6	21 Jul	05:22		-1 hr 39 min
 
S=5	  "	15:07		+29 minutes
 
T=4	  "	18:04		+04 minutes
 
U=3	  "	21:47           +40 minutes
 
V=2	22 Jul  03:57		-34 minutes
 
W=1	  "     07:53		+41 minutes
 
===================================================================
 
 
 
HST Shoemaker-Levy/Jupiter campaign
Scheduling results of SOT meeting 1/27-28 1994
 
*****************P/SL9 Timeline Revision History*******************
 
23 Feb 94:  Extended version from Y. Wang.
___________________________________________________________________
 
01 Mar 94:  Revised by R. Landis to account for new impact times.
___________________________________________________________________
 
03 Mar 94:  Revised by R. Landis per A. Storrs via R. Prangee.  
	    Changing orbit 12 observation to orbit 20.  94.234 ob-
	    servations changed to day 94.220.
 
	    Deleted fragments J and M from timeline as these do not
	    appear in most recent HST images.
___________________________________________________________________
 
14 Mar 94:  Renumbered timeline orbits per Y. Wang.  (Numbered se-
	    quence has been corrected.)
 
	    Tabs replaced with spaces in order to better enable
	    H. Hammel's program to utilize this timeline.
___________________________________________________________________
 
07 Apr 94:   Updated A. Storrs/R. Landis.
 
___________________________________________________________________
 
29 Apr 94:   Updated A. Storrs/R. Landis.  
 
	     Revised by R. Landis to account for new impact times
	     based on JPL data from D. Yeomans/P. Chodas.
 
___________________________________________________________________
	   
02 Jun 94:   Revised by R. Landis to account for new impact times
	     based on JPL data from P. Chodas.
 
___________________________________________________________________
 
07 Jun 94:   Included Weaver's last P/SL 9 observations.  Updated
	     HST orbit times based upon SPSS' most recent HST
	     ephemeris.  R. Landis/A. Storrs.
 
___________________________________________________________________
 
15 Jun 94:   Added Shemansky's FOS two-orbit sequence for o/a the 
             94.213 SMS.
 
             Revised by R. Landis to account for new impact times
             based on JPL data from P. Chodas.
___________________________________________________________________
 
16 Jun 94:   Removed the day 195 ("non-specific" time) observations
             from timeline.  These are vestigial as R. Prange and
             K. Noll have specific time slots/HST orbits for their
             respective FOC and FOS/HRS observations.
___________________________________________________________________
 
28 Jun 94:   Revised by R. Landis to account for new impact times
             based on JPL data from P. Chodas.  The predicted
	     impact times continue to slip earlier, but only by an
             order of a few minutes since the last impact update 
	     made on 15 Jun 94.  Impact times for fragments A, B, R, 
	     and S made larger jumps (15 to 20 minutes earlier), and 
	     the times for T and U have changed the most (30 minutes 
             and an hour earlier, respectively).  
___________________________________________________________________
 
06 Jul 94:   Updated per A. Storrs.
 
             Revised by R. Landis to account from new impact times
	     based on JPL data from P. Chodas.  The orbit solutions
	     are based on the most recent (as recent as 4 Jul 94) 
	     astrometry.  
 
	     The predicted impact times are generally/roughly 5 to 
	     10 minutes earlier (than the previous version of this 
             timeline) for the major fragments.  However, fragments 
             A and D impact 24 and 29 minutes later.  1-sigma 
             uncertainty is now 6 to 8 minutes.
___________________________________________________________________
 
Orb# Starting Time:   SAA               Activity:
			(start--end)
 
		***11 July 1994***
 
    192:19:12:00                        WFPC SL9Q-- Weaver
    192:20:48:33                        WFPC SL9Q-- Weaver
    192
 
		***12 July 1994***
 
    193
 
		***13 July 1994***
 
    194
    194:14:38:36                        FOC-- Prange
    194:16:15:08
    194:17:51:40
    194:19:28:11                        HRS-- Noll
    194:21:04:43                        FOC-- Prange
    194:22:41:15  23:17--end   (05)
 
		***14 July 1994***
 
    195:00:17:47  00:51--end   (05)
                  00:56--01:07 (02)
    195:01:54:19  02:30--end   (05)
                  02:34--end   (02)
    195:03:30:50  04:12--end   (05)
                  04:14--end   (02)
    195:05:07:22  05:54--end   (05)
		  05:56--end   (02)
    195:06:43:54  07:37--end   (05)
    195:08:20:23                        WFPC SL9G-- Weaver
    195:09:56:55                        WFPC SL9G-- Weaver
    195:11:37:45                        FOS  SL9G-- Weaver
    195:13:09:59                        FOS  SL9G-- Weaver
    195:14:50:40                        WFPC SL9S-- Weaver
    195:16:23:01                        WFPC SL9S-- Weaver
    195:17:59:36                        FOS-- Noll
    195:19:36:08
    195:21:12:39  21:47--22:02 (05)
    195:22:49:11   
                    
		***15 July 1994***
 
    196:00:25:42                       
    196:02:02:14                       
    196:03:38:45  04:20--end   (05)
                  04:23--end   (02)
    196:05:15:18  06:03--end   (05)
                  06:05--end   (02)
    196:06:51:49  07:46--end   (05)
    196:08:28:21
    196:10:04:52
1   196:11:41:24                        WFPC map-- Hammel
2   196:13:17:55                        WFPC map-- Hammel
3   196:14:54:27                 	WFPC map-- Hammel
4   196:16:30:59                 	WFPC map-- Hammel
5   196:18:07:30                 	WFPC map-- Hammel
6   196:19:44:01                 	WFPC map-- Hammel
 
7   196:21:20:32  21:51--22:11 (05)
8   196:22:57:04  23:27--end   (05)
                  23:32--23:42 (02)
 
		***16 July 1994***
 
9   197:00:33:36  01:06--end   (05)
                  01:09--01:25 (02)
10  197:02:10:07  02:46--end   (05)
                  02:49--end   (02)
11  197:03:46:38  04:27--end   (05)
                  04:31--end   (02)
12  197:05:23:09  06:11--end   (05)
                  06:14--end   (02)
13  197:06:59:42  07:54--end   (05)
14  197:08:36:13
15  197:10:12:44
16  197:11:49:15                        
17  197:13:25:47                   	    
18  197:15:02:18                   	    
19  197:16:38:49
20  197:18:15:21                                              
21  197:19:51:06  20:35--20:46 (05)     WFPC-- Hammel         A impact 197:19:54
22  197:21:28:23  21:56--22:19 (05)
23  197:23:04:54  23:34--end   (05)
                  23:37--23:51 (02)
 
		***17 July 1994***
 
24  198:00:41:26  01:17--end   (05)
                  01:16--01:34 (02)
25  198:02:17:57  02:55--end   (05)                           B impact 198:02:49
                  02:57--end   (02)                           
26  198:03:54:28  04:37--end   (05)
                  04:39--end   (02)
27  198:05:30:59  06:20--end   (05)                           
                  06:22--end   (02)                           C impact 198:06:56
28  198:07:07:31                        
29  198:08:43:14                        WFPC-- Clarke
30  198:10:20:32                                              
31  198:11:57:04                                              D impact 198:11:42
32  198:13:33:35                        WFPC-- Hammel         
33  198:15:10:06                        WFPC-- Hammel         E impact 198:15:04
34  198:16:46:38                        WFPC-- Hammel
35  198:18:23:09                        WFPC-- 1/2 Hammel, 
                                               1/2 Clarke
36  198:19:59:39  20:26--20:45 (05)
37  198:21:36:11  22:02--22:28 (05)
                  22:07--22:15 (02)
38  198:23:12:42  23:41--end   (05)     3 WFPC DARKS
                  23:45--00:04 (02)
 
     *** SMS BOUNDARY *** *** BEGIN 94.199 SMS *** *** SMS BOUNDARY *** 
 
		***18 July 1994**
 
39  199:00:34:04  01:21--end   (05)                           F impact 199:00:28
                  01:24--01:42 (02)
40  199:02:10:24: 03:03--end   (05)                           
                  03:05--03:24 (02)
41  199:03:48:43  04:35--end   (05)
                  04:48--end   (02)
42  199:05:38:47  06:28--end   (05)     FOC--Prange          
43  199:07:15:18                        WFPC-- Hammel         G impact 199:07:28
44  199:08:51:49                        WFPC-- Hammel
45  199:10:28:20                        FOS-- Noll
46  199:12:04:51
47  199:13:41:22                        WFPC-- Clarke
48  199:15:17:52                        WFPC SL9K-- Weaver
49  199:16:54:24
50  199:18:30:55                        HRS-- Noll (SiO)      H impact 199:19:26
51  199:20:07:27  20:32--20:54 (05)
52  199:21:43:58  22:09--22:36 (05)
                  22:14--22:25 (02)
53  199:23:20:29  23:48--end   (05)
                  23:52--00:07 (02)
 
		***19 July 1994***
 
54  200:00:57:00  01:28--end   (05)
                  01:32--01:51 (02)
55  200:02:33:30  03:12--end   (05)
                  03:14--end   (02)                               	     
56  200:04:10:02  04:55--end   (05)    	    	
                  04:57--end   (02)
57  200:05:48:33  06:37--end   (05)     HRS-- Noll (SiO)
                  06:39--end   (02)
58  200:07:23:04                        WFPC-- Hammel
59  200:08:59:35                        WFPC-- Hammel         K impact 200:10:18
60  200:10:36:06                        WFPC-- 1/2 Hammel,    
                                               1/2 Clarke
61  200:12:12:37                        WFPC SL9L-- Weaver
62  200:13:49:08                        
63  200:15:25:39                        HRS-- Noll (G140L)
64  200:17:02:11
65  200:18:38:41  19:09--19:18 (05)
66  200:20:15:13  20:37--21:02 (05)
                  20:45--21:46 (02)
67  200:21:51:43  22:17--22:45 (05)                           
                  22:21--22:34 (02)
68  200:23:28:14  23:55--end   (05)     3 WFPC DARKS          L impact 200:22:07
                  23:59--00:16 (02)
 
		***20 July 1994***
 
69  201:01:04:46  01:37--end   (05)
                  01:40--01:59 (02)
70  201:02:41:16  03:20--end   (05)
                  03:22--end   (02)
71  201:04:17:48  05:03--end   (05)
                  05:05--end   (02) 
72  201:05:54:18  06:46--end   (05)
                  06:48--end   (02)    
73  201:07:32:24                       WFPC SL9Q-- Weaver    
74  201:09:07:20                       WFPC SL9Q-- Weaver     N impact 201:10:19
75  201:10:43:52                       HRS-- Noll (G140L)
76  201:12:20:22                       HRS-- Noll (G140L)
77  201:13:56:54                       WFPC-- Prange (4 ex)                    
78  201:15:33:25                       WFPC-- 1/2 Hammel,    P2 impact 201:15:05
                                              1/2 Clarke
79  201:17:09:55                       WFPC SL9S-- Weaver
80  201:18:46:27  19:07--19:27 (05)                          Q2 impact 201:19:32
81  201:20:22:58  20:45--21:11 (05)    WFPC-- Hammel         Q1 impact 201:19:59
                  20:50--20:59 (02)
82  201:21:59:30  22:23--22:53 (05)
                  22:27--22:42 (02)
83  201:23:38:00  00:04--end   (05)
                  00:07--00:24 (02)
 
		***21 July 1994***
 
84  202:01:12:32  01:45--end   (05)
                  01:48--end   (02)
85  202:02:49:02  03:27--end   (05)
                  03:31--end   (02)
86  202:04:25:34  05:11--end   (05)
                  05:13--end   (02)                           R impact 202:05:22
87  202:06:02:05  06:54--end   (05)     WFPC-- Hammel         
88  202:07:38:35                        WFPC-- 1/2 Hammel, 
                                               1/2 Clarke
89  202:09:15:07                        WFPC-- Hammel
90  202:10:51:37                        WFPC-- Hammel
91  202:12:28:09                        WFPC-- 1/2 Hammel,
                                               1/2 Clarke
92  202:14:04:40                                              S impact 202:15:07
93  202:15:41:11                        FOS-- Noll            
94  202:17:17:42                        HRS-- Noll (G140L)    T impact 202:18:04
95  202:18:54:12  19:14--19:37 (05)
96  202:20:30:44  20:52--21:19 (05)
                  20:56--21:08 (02)                           
97  202:22:07:15  22:31--23:00 (05)                           U impact 202:21:47
                  22:34--22:51 (02)
98  202:23:43:46  00:12--end   (05)     3 WFPC DARKS          
                  00:14--00:33 (02)
 
		***22 July 1994***
 
99  203:01:20:17  01:54--end   (05)
                  01:56--end   (02)
100 203:02:56:48  03:37--end   (05)
                  03:39--end   (02)                           V impact 203:03:57
101 203:04:33:19  05:20--end   (05)     WFPC-- Hammel               
                  05:22--end   (02)
102 203:06:09:50  07:03--end   (05)     WFPC-- Hammel
103 203:07:46:22                        WFPC-- Hammel         W impact 203:07:53
104 203:09:22:52                        WFPC-- 1/2 Hammel, 
                                               1/2 Clarke
105 203:10:59:23                        
106 203:12:35:35                        HRS-- Noll (SiO,2x12)
107 203:14:12:25                        HRS-- Noll (SiO, 3x8)
108 203:15:48:57
109 203:17:25:28  17:49--18:02 (05)
110 203:19:01:59  19:20--19:45 (05)
                  19:26--19:31 (02) 
111 203:20:38:30  20:54--21:27 (05)
                  21:03--21:17 (02)
112 203:22:15:01  22:37--23:08 (05)
                  23:42--22:59 (02)
113 203:23:51:32  00:20--end   (05)
                  00:23--00:42 (02)
 
		***23 July 1994***
 
114 204:01:28:04  02:03--end   (05)
                  02:05--end   (02)
115 204:03:04:34  03:46--end   (05)
                  03:48--end   (02)
116 204:04:41:05  05:27--end   (05)
                  05:31--end   (02)
117 204:06:17:37  07:11--end   (05)      WFPC map-- Hammel
118 204:07:54:08                         WFPC map-- Hammel
119 204:09:30:39                         WFPC map-- Hammel
120 204:11:07:09 	                 WFPC map-- Hammel
121 204:12:43:41                         WFPC map-- Hammel
122 204:14:20:12  	                 WFPC map-- Hammel
123 204:15:56:43
124 204:17:33:14  17:51--18:11 (05)
125 204:19:09:46  19:27--19:54 (05)
                  19:32--19:42 (02)
126 204:20:46:17  21:06--21:35 (05)
                  21:10--21:25 (02)
127 204:22:22:48  22:46--23:15 (05)
                  22:49--23:07 (02)
128 204:23:59:19  00:27--end   (05)
                  00:31--00:50 (02)
 
		***24 July 1994***
 
129 205:01:35:50  02:12--end   (05)
                  02:14--end   (02)
130 205:03:12:22  03:54--end   (05)
                  03:56--end   (02)
131 205:04:48:53  05:37--end   (05)
                  05:39--end   (02)
132 205:06:25:23                        HRS-- McGrath
133 205:08:01:54                        HRS-- McGrath
134 205:09:38:25                        HRS-- McGrath
135 205:11:14:57                        HRS-- McGrath
136 205:12:51:28                        HRS-- McGrath
137 205:14:27:59                        
138 205:16:04:30  16:33--16:34 (05)     HRS(Side 2)--McGrath
139 205:17:41:01  17:56--18:20 (05)
140 205:19:17:32  19:35--20:02 (05)
                  19:38--19:51 (02)
141 205:20:54:04  21:13--21:48 (05)
                  21:17--21:33 (02)
142 205:22:30:36  22:55--23:23 (05)
                  22:57--23:16 (02)
    .
 
    .
 
    .
 
     *** SMS BOUNDARY *** *** BEGIN 94.206 SMS *** *** SMS BOUNDARY ***     
 
		***25 July 1994***
    206
    
    .
    
    .
 
    .
 
		***26 July 1994***
 
    207:23:40:00
 
		***27 July 1994***
 
    208:00:52:45  00:55--01:18 (05)
                  00:57--01:14 (02)
    208:02:29:22  02:37--02:57 (05)
                  02:39--02:54 (02)
    208:04:05:55  04:20--04:36 (05)
                  04:22--04:28 (02)
    208:05:42:31  06:05--06:09 (05)      
    208:06:48:55                         FOS-- McGrath
    208:08:25:26                         FOS-- McGrath
    208:10:01:57                         FOS-- McGrath
    208:11:38:29                         FOS-- McGrath
    208:13:15:00                         FOS-- McGrath
    208:14:51:32  15:12--15:18 (05)      FOS-- McGrath
    208:16:28:04  16:38--17:03 (05)
    208:18:04:35  18:17--18:44 (05)
                  18:21--18:34 (02)
    208:19:41:07  20:56--20:26 (05)
                  19:59--20:12 (02)
    208:21:17:39  21:37--22:06 (05)
                  21:40--21:58 (02)
    208:22:54:11  23:20--23:46 (05)
                  23:22--23:41 (02)
 
		***28 July 1994***
 
    209:00:30:42  01:03--01:25 (05)
                  01:05--01:22 (02)
    .
 
    .
 
    .
 
		***29 July 1994***
 
    210:04:22:14  04:37--04:47 (05)
    210:05:58:46
    210:07:35:18                         
    210:08:41:17                         WFPC-- Clarke
    210:10:17:48
    210:11:54:20
    210:13:30:52
    210:15:07:23  15:15--15:37 (05)
    210:16:43:55  16:52--17:19 (05)
                  16:57--17:08 (02)
    210:18:20:27  18:31--19:00 (05)
                  18:34--18:51 (02)
    210:19:56:59  20:12--20:41 (05)
                  20:15--20:33 (02)
    210:21:33:31  21:54--22:21 (05)
                  21:57--22:16 (02)
    210:23:10:03  23:37--00:00 (05)
                  23:39--23:57 (02)
 
		***30 July 1994***
 
    211:00:46:35  01:20--01:40 (05)
                  01:22--01:36 (02)
    211:02:23:07  03:02--end   (05)
                  03:06--03:10 (02)
    211:03:59:39  04:48--04:50 (05)
    211:05:36:10
    211:07:12:42                         WFPC map-- Hammel
    211:08:49:14                         WFPC map-- Hammel
    211:10:25:46                         WFPC map-- Hammel
    211:12:02:18                         WFPC map-- Hammel
    211:13:38:50  13:52--14:02 (05)
 
    .
 
    .
		***31 July 1994***
    .
 
     *** SMS BOUNDARY *** *** BEGIN 94.213 SMS *** *** SMS BOUNDARY *** 
 
    .
		***01 August 1994***
    .
 
    213:                                FOS-- Shemansky (2 orbits)
    .
 
    .
     *** SMS BOUNDARY *** *** BEGIN 94.220 SMS *** *** SMS BOUNDARY *** 
    		
		***08 August 1994***
 
    220:21:41:07  begin--21:54 (05)
                  begin--21:48 (02)
    220:23:17:35  23:21--23:29 (05)
 
		***09 August 1994***
 
    221:00:54:04                         
    221:02:06:06                         FOC-- Prange
    221:03:42:36
    221:05:19:08
    221:06:55:40
    221:08:32:10                         FOC--  Prange
    221:10:08:42  begin--10:20 (05)      FOS-- Noll
    221:11:45:13  begin--12:03 (05)
                  begin--11:51 (02)
 
    .
 
    .
 
    .
 
 
		***10 August 1994***
 
    222:20:18:50  begin--20:29 (05)
                  begin--20:25 (02)
    222:21:55:18  begin--22:07 (05)      
    222:23:08:39                         HRS-- Noll
 
		***11 August 1994***
 
    223:00:45:10                         
    223:02:21:41
    223:03:58:12
    223:05:34:44
    223:07:11:14
    223:08:47:45  begin--08:54 (05)
 
    .
 
    .
 
    .
 
		**12 August 1994***
 
    224:02:29:27
    224:04:05:57
    224:05:42:28                         
    224:07:18:59
    
    .
 
    .
 
    .
     *** SMS BOUNDARY *** *** BEGIN 94.227 SMS *** *** SMS BOUNDARY ***     
 
    .
		***15 August 1994***
    .
 
    .
 
     *** SMS BOUNDARY *** *** BEGIN 94.234 SMS *** *** SMS BOUNDARY ***     
 
    .
		***22 August 1994***
    .
 
    .
 
		***24 August 1994***
 
    236:15:32:13
    236:17:08:42
    236:18:45:10                         
    236:20:08:48                         FOS-- Noll
    236:21:45:21                         WFPC-- Hammel
    
    .
 
    .
 
    .
 
 
           ### NOMINAL END OF JUPITER-COMET CAMPAIGN ###
 
 
Three digit numbers are day of year (1994): day 197 is July 16.
All times are UT (at Earth). Orbit times are based upon extrapolation 
done in May 1994. 
 
All times subject to change due to uncertainty in extrapolation of HST's 
orbit and in prediction of impact times.
 
Note that FGS control cannot be used between 197:06 and 198:13, due to 
the proximity of Jupiter to the Moon.
 
Each orbit (visibility period) lasts 52 min. In the SAA duration column, 
ending time labeled "end" means it lasts until the visibility period of 
the HST ends. 
 
The numbers of the orbits here are rather arbitrary.  Orbit # 1 here 
corresponds to orbit No. 23031 from HST's numbering convention. 
 
 
							ATTACHMENT B
 
                                                              
		HST, Jupiter, and Comet Bibliography
 
Popular Books
 
Kerr, Richard and Elliot, James, Rings:  Discoveries from Galileo 
to Voyager, The MIT Press, Cambridge, Massachusetts, 1984.
 
Littman, Mark, Planets Beyond:  Discovering the Outer Solar System, 
Wiley Science Editions, New York, New York, 1988.
 
Peek, Bertrand M., The Planet Jupiter:  The Observer's Handbook, 
Faber & Faber Limited, London, England, 1958 [revised, 1981].
 
Smith, Robert W., The Space Telescope:  A Study of NASA, Science, 
Technology and Politics, Cambridge University Press, Cambridge, 
England, 1989 [revised, 1993].
 
Shea, J.F. et al., Report of the Task Force on the Hubble Space 
Telescope Servicing Mission (1993).
 
Magazine Articles
 
Articles on HST and Comet P/Shoemaker-Levy have appeared in popular 
magazines such as Astronomy, Sky & Telescope, Mercury, Discover, 
Science News, New Frontier, and The Planetary Report.
 
Asker, James R., "Spacecraft Armada to Watch Comet Collide with 
Jupiter," Aviation Week & Space Technology, 24 January 1994.
 
Chaisson, E.J. and Villard, R., "Hubble Space Telescope:  The Mission," 
Sky & Telescope, April, 1990.
 
Fienberg, Richard T., "HST:  Astronomy's Discovery Machine," Sky & 
Telescope, April, 1990.
 
Fienberg, Richard T. "Hubble's Road to Recovery," Sky & Telescope, 
November 1993.
 
Hawley, Steven A., "Delivering HST to Orbit," Sky & Telescope, April 1990.
 
Hoffman, Jeffrey A., "How We'll Fix the Hubble Space Telescope," Sky 
& Telescope, November 1993.
 
Landis, Rob, "Jupiter's Ethereal Rings," Griffith Observer, May 1991.
 
O'Dell, C.R., "The Large Space Telescope Program," Sky & Telescope, 
December 1972.
 
Peterson, Ivars, "Jupiter's Model Spot," Science News, 19 February 1994.
 
Smith, Douglas L., "When a Body Hits a Body Comin' Through the Sky," 
Caltech Alumni Magazine Engineering & Science, Fall 1993.
 
Tucker, W., "The Space Telescope Science Institute," Sky & Telescope, 
April 1985.
 
Villard, Ray, "From Idea to Observation:  The Space Telescope at Work,"
Astronomy, June, 1989.
 
Villard, Ray, "The World's Biggest Star Catalogue," Sky & Telescope, 
December 1989.
 
Scientific Articles
 
HST science results are published in professional journals 
such as Geophysical Research Letters, Icarus, Astronomical 
Journal, Astrophysical Journal, Nature, Science, Scientific 
American, and Space Science Reviews, as well as in the pro-
ceedings of professional organizations.  Some specific articles 
of interest include:
 
 
Chevalier, Roger A. and Sarazin, Craig L., "Explosions of 
Infalling Comets in Jupiter's Atmosphere," submitted to 
Astrophysical Journal, 20 July 1994.
 
Kerr, Richard A., "Jupiter Hits May be Palpable Afterall," 
Science, 262:505, 22 October 1993.
 
Melosh, H.J. and Schenk, P., "Split Comets and the Origin of 
Crater Chains on Ganymede and Callisto," Nature, 365:731-733, 
21 October 1993.
 
Scotti, J.V. and Melosh, H.J., "Estimate of the Size of Comet 
Shoemaker-Levy 9 from a Tidal Breakup Model," Nature, 365:733-735, 
21 October 1993.
 
Trepte, C.R. and Hitchman, M.H., "The Stratospheric Tropical
Circulation Deduced from Aerosol Satellite Data," Nature 335:
626-628 (1992).
 
Weaver, H.A. et al., "Hubble Space Telescope Observations 
of Comet P/Shoemaker-Levy 9 (1993e)," Science, 263:787-790, 
11 February 1994.
 
 
							ATTACHMENT C
 
Abbreviations/Acronym List
 
COSTAR  Corrective Optics Space Telescope Axial Replacement
 
ESA  European Space Agency
 
EVA  Extravehicular Activity
 
FOC  Faint Object Camera
 
FOS  Faint Object Spectrograph
 
FGS  Fine Guidance Sensor
 
GO  General Observer (also Guest Observer)
 
GHRS  Goddard High Resolution Spectrograph, also referred to as HRS.
 
GTO  Guaranteed Time Observer
 
HST  Hubble Space Telescope
 
IR  Infrared
 
JPL  Jet Propulsion Laboratory
 
LEO Low-Earth Orbit
 
MT Moving Targets or Moving Targets Group (at STScI)
 
NASA  National Aeronautics and Space Administration
 
NICMOS  Near-Infrared Camera and Multi-Object Spectrometer
 
OSS  Observation Support Branch (at STScI)
 
P/SL9  Shorthand for Periodic Comet Shoemaker-Levy 9 (SL9-A 
       refers to one of the cometary fragments, in this example 
       fragment "A", of the comet)
 
RSU  Rate-sensing unit (gyroscope)
 
SAA  South Atlantic Anomaly
 
SADE  Solar Array Drive Electronics
 
SMOV  Servicing Mission Observatory Verification
 
SPB  Science Planning Branch (at STScI)
 
SPSS  Science Planning & Scheduling Branch (at STScI)
 
SOT  Science Observation Team
 
STIS  Space Telescope Imaging Spectrograph
 
STS-61  Space Transportation System; the first servicing mission 
	is the 61st shuttle mission on the manifest since the 
	space shuttle first flew in 1981.
 
STScI  Space Telescope Science Institute.
 
WF/PC  (pronounced "wif-pik")  Wide Field/Planetary Camera
 
 
						ATTACHMENT D
 
 
A variety of line art supplied by JPL, Lowell Observatory, 
the University of Maryland-College Park, and the STScI.  
Most is self-explanatory.
 
                                                ATTACHMENT E
 
 
NEWSROOM HOURS AND TV COVERAGE FOR COMET SHOEMAKER-LEVY 9
 
        NASA's coverage of the impact of Comet P/Shoemaker-Levy 
9 during the week of July 16-22 includes a series of live, 
televised press briefings and a 24-hour newsroom operation at 
the Goddard Space Flight Center (GSFC), Greenbelt, Md.
 
        The Goddard Comet Impact newsroom will be the central 
location providing coverage of observations and images from 
the worldwide network of ground-based observatories and 
spacecraft taking part in the NASA/National Science Foundation 
observing project.  Scientists will be on hand at the newsroom 
to answer questions, or interviews can be arranged as needed.  
Press materials, artwork and video relating to the event will 
be available to media.  
 
        The first fragment of the comet will impact Jupiter just 
before 4 p.m. EDT on the side of Jupiter facing away from 
Earth.  Shortly afterwards, the point of impact will rotate 
into view as seen from Earth.  The first image of the impact 
area is expected to be available (following minimal 
processing) at about 10 p.m. EDT.
 
        NASA will release the image in a live program broadcast 
from the Space Telescope Science Institute, Baltimore, Md., 
starting at 10 p.m. EDT.  There will be no press briefing on 
NASA TV at that time, however, a briefing will be held Sunday 
morning at the Goddard Comet Impact Newsroom.
 
Press Briefing Schedule
 
        At 8:00 a.m. EDT, Sunday, July 17, a press briefing 
will be broadcast live on NASA TV with Q & A from other NASA 
Centers, and will include updated information about the first 
impact and the image.  During the following week, NASA will 
hold a live press briefing each day at the GSFC Comet Impact 
Newsroom (see schedule below).
 
        The briefing panels will include Comet co-discoverers 
Drs. Eugene and Carolyn Shoemaker and David Levy on most days 
as well as scientists presenting images and information from 
the Hubble Space Telescope and other spacecraft.  Dr. Lucy 
McFadden will have a round-up of observations from ground-
based observatories around the world.  The program and 
briefing schedule follows:
 
JULY DATE       TIME (EDT)      EVENT
Sat.    16      10:00 p.m.      Live from STScI: First 
				Impact Image Release
                                (no Q & A Centers)
Sun.    17       8:00 a.m.      Press Briefing at GSFC
Mon.    18       8:00 a.m.      Press Briefing at GSFC
Tue.    19       8:00 a.m.      Press Briefing at GSFC
Wed.    20      12:00 noon      Press Briefing at GSFC
Th.     21       8:00 a.m.      Press Briefing at GSFC
Fri.    22       9:30 a.m.      Press Briefing at GSFC
Sat.    23       8:00 a.m.      Press Briefing at GSFC
 
Note:  The above times are dependent on the STS-65 mission 
schedule.  If there is a change in the launch or landing time 
of the Shuttle, the program times will change.  
 
Comet Impact Newsroom Operations
 
        The newsroom will operate on a 24-hour basis beginning 
at 6 a.m., Sun., July 17 until noon EDT, July 23.  The 
newsroom will be located at the Goddard Visitor's Center on 
Soil Conservation Road in Greenbelt.  The phone number for the 
newsroom will be 301/286-2300, but will not be active until 6 
a.m., July 17.  
 
        Media wishing to use the newsroom must register at the 
Visitor Center and obtain a media badge, starting at 6 a.m. 
EDT July 17.  Valid press credentials and a photo ID must be 
presented.  Media representatives who are not U.S. citizens 
must contact the Goddard Office of Public Affairs at 301/286-
8955 before registering.
 
Video Uplink Schedule
 
        NASA will provide feeds of b-roll and animation of the 
comet impacts with Jupiter on the following schedule:  
 
June 29:        10:00 a.m. and 1:30 p.m. EDT
June 30:        10:30 a.m. and 1:30 p.m. EDT
July 5: 	10:30 a.m. and 1:30 p.m. EDT
July 15:        1:00 p.m. EDT
 
        Also on July 5, NASA Television will replay the May 18 
press briefing with panelists Dr. Eugene Shoemaker, Dr. Heidi 
Hammell, Dr. Hal Weaver, Dr. Lucy McFadden and Dr. Melissa McGrath.
 
NASA Select is carried on Spacenet 2, transponder 5, channel 9, 
69 degrees West, transponder frequency is 3880 MHz, audio sub-
carrier is 6.8 MHz, polarization is horizontal. 
 
Facts at a Glance
=================
 
One-way light time, Jupiter to Earth:  43 minutes
 
Radius of Jupiter:		       71,350 km (equatorial)
				       67,310 km (polar)	
Radius of Earth:		       6378 km (equatorial)
				       6357 km (polar)
P/Shoemaker-Levy:		       4.5? km (equivalent sphere)
P/Halley:			       7.65 x 3.60 x 3.61 km
Mass of Jupiter:		       1.90 x 1030 g (~318 Earth masses)
Rotation period:		       9 hours 56 minutes
Number of known moons:		       16
Discovery date P/Shoemaker-Levy:       24 March 1993
Time of first impact (P/SL9-A):	       16 July 1994, 19:54 UTC
Time of P/SL9-Q's impact:	       20 July 1994, 19:32 UTC
Time of last impact (P/SL9-W):	       22 July 1994, 07:53 UTC
HST deployment date:		       25 April 1990
HST first servicing mission:	       2 - 13 December 1993
Diameter of HST's primary mirror:      2.4 meters
 
 
Acknowledgements
 
This document would not be possible if not for the support 
of the Science Observation Team and the Science Planning 
Branch/Moving Targets Group at the Space Telescope Science 
Institute.  The selection of material and any errors are
the sole responsibility of the author.
 
This paper represents the combined efforts of scientists, 
educators, and science writers; it is a selected compilation 
of several texts, original manuscript, and submitted paragraphs.  
Gratitude and many thanks go to Mike A'Hearn (University of 
Maryland), Reta Beebe (New Mexico State University), Ed Bowell 
(Lowell Observatory), Paul Chodas (JPL), John Clarke (University 
of Michigan), Ted Dunham (NASA-Ames), Heidi Hammel (MIT), Joe 
Harrington (MIT),  Dave Levy, Chris Lewicki (SEDS-University of 
Arizona), Mordecai MacLow (University of Chicago), Lucy-Ann 
McFadden (University of Maryland), Melissa McGrath (STScI), 
Ray Newburn (JPL), Keith Noll (STScI), Elizabeth Roettger (JPL), 
Jim Scotti (University of Arizona), Dave Seal (JPL), Carolyn & 
Gene Shoemaker, Zdenek Sekanina (JPL), Ed Smith (STScI), Lawrence 
Wasserman (Lowell Observatory), Hal Weaver (STScI), Bob West (JPL), 
Don Yeomans (JPL) and to all others who may have been omitted.
 
All comments should be addressed to the author/editor:
 
Rob Landis
Space Telescope Science Institute
Science Planning Branch/Moving Targets Group
3700 San Martin Drive,
Baltimore, MD  21218
 

From:	US4RMC::"[email protected]" "MAIL-11 Daemon"  7-JUL-1994 18:49:34.36
To:	Multiple recipients of list <[email protected]>
CC:	
Subj:	Abbreviated HST Mission/Comet Impact Timeline

The times below are based upon the orbit solutions of 5 July 1994.

This is an abbreviated timeline.  All times are EDT. Impact times
account for light travel time back to Earth (from Jupiter).  Note that
from from 2:00 AM EDT, 16 July through 9:00 AM EDT, 17 July FGS
control cannot be used due to the proximity of the Moon to Jupiter. 
Spacecraft will be under gyroscopic control. 

++Rob Landis, STScI, Baltimore, MD
  Moving Targets

Observation Start Time/             Activity:
Impact Time (EDT):

Wednesday, 13 July 1994

    10:39 AM                        Pre-impact examination 
			            of Jovian aurorae (FOC)
    
     3:28 PM                        Pre-impact baseline 
		       		    spectroscopic obser-
			            vations of Jupiter (HRS)

     5:05 PM                        More pre-impact examination
                                    of Jovian aurorae (FOC)

Thursday, 14 July 1994

     4:20 AM                        Last look at "G"; 2-orbit
			            imaging sequence (WFPC)
				    

     7:38 AM                        Spectroscopy of fragment 
				    "G"; 2-orbit sequence (FOS)


    10:51 AM                        Images of fragment "S";
				    2-orbit sequence (WFPC)
 
     1:59 PM                        Pre-impact spectroscopy of 
				    Jupiter (FOS)

Friday, 15 July 1994
 
                                     
     7:41 AM      		    6-orbit mapping sequence 
			            of Jupiter (WFPC)

Saturday, 16 July 1994

     
     3:54 PM                        *A IMPACTS JUPITER*

     3:51 PM                        Image of 1st impact site on
				    Jupiter (WFPC)

     7:30 PM*			    FIRST PRESS CONFERENCE
				    STScI Auditorium
                                    SOT Lead Members
				    (time subject to change)
	
    10:49 PM                        *B IMPACTS JUPITER*
				    (no HST observations due to 
			             spacecraft entering SAA over
                                     several consecutive orbits)
                                    
Sunday, 17 July 1994

     2:56 AM			    *C IMPACTS JUPITER*

     4:43 AM                        UV Imaging of Jupiter's
                                    upper atmosphere (WFPC)

     7:42 AM                        *D IMPACTS JUPITER*

     8:00 AM			    Press Briefing at GSFC

     9:34 AM                        5-orbit mapping sequence
				    of Jupiter (WFPC)

    11:04 AM                        *E IMPACTS JUPITER*

     8:28 PM			    *F IMPACTS JUPITER*
                                     (no HST observations due to 
			             spacecraft entering SAA over
                                     several consecutive orbits)
                                   
Monday, 18 July 1994


     1:39 AM                        Jovian Aurora (FOC)

     3:15 AM                        Mapping of Jupiter (WFPC)

     3:28 AM		            *G IMPACTS JUPITER*
				    (brightest fragment in 
                                     comet train)

     4:52 AM                        Mapping of Jupiter (WFPC)

     6:28 AM                        Spectroscopic search for
				    new species in Jupiter's
				    atmosphere (FOS)

     8:00 AM			    Press Briefing at GSFC

     9:41 AM                        UV imaging; Jupiter's upper
				    atmosphere (WFPC)

    11:18 AM                        Last look at fragment "K" (WFPC)

     2:31 PM                        Spectroscopic search for SiO
			            deposited into Jupiter's 
				    atmosphere (HRS)

    
     3:26 PM			    *H IMPACTS JUPITER*
                                    (no HST observations due
			             to s/c transiting SAA)
                                     
Tuesday, 19 July 1994

     1:49 AM                        Spectroscopic search for
				    SiO deposition (HRS)
                
     3:23 AM                        4-orbit mapping sequence
				    of Jupiter (WFPC)

     6:18 AM			    *K IMPACTS JUPITER*

     8:00 AM			    Press Briefing at GSFC

     9:49 AM                        Last observation of 
			            fragment "L" (WFPC)
				    
    11:26 AM                        Jupiter spectroscopy (HRS)

				
     6:07 PM			    *L IMPACTS JUPITER*
				     (no HST observations due
			             to s/c transiting SAA)

Wednesday, 20 July 1994


     5:07 AM                        Last images of "Gang of Four";
				    Q, P fragments (WFPC)

     6:19 AM			    *N IMPACTS JUPITER*

     6:44 AM                        Spectroscopic observations
                                    of Jupiter; 2 orbits (HRS)

     9:57 AM                        Jupiter imaging (WFPC)

    11:05 AM                        *P2 IMPACTS JUPITER*
                    
    11:33 AM                        Jupiter imaging (WFPC)

    12:00 NOON			    Press Briefing at GSFC

     1:10 PM                        Last look at "S" (WFPC)

     3:32 PM			    *Q2 IMPACTS JUPITER*
     3:59 PM			    *Q1 IMPACTS JUPITER*

     4:23 PM                        Jupiter imaging (WFPC)

Thursday, 21 July 1994

     1:22 AM                        *R IMPACTS JUPITER*
				    
				    
     2:02 AM                        5-orbit mapping sequence
                                    of Jupiter (WFPC)

     8:00 AM			    Press Briefing at GSFC

    11:07 AM			    *S IMPACTS JUPITER*

    11:41 AM                        Spectroscopic observations
				    of Jupiter (FOS)

     1:18 PM                        Spectroscopic observations
				    of Jupiter (HRS)

     2:04 PM	                    *T IMPACTS JUPITER* \ No HST
							 |observing,
     5:47 PM			    *U IMPACTS JUPITER*  |due to SAA
				                         |impacted 
    11:57 PM			    *V IMPACTS JUPITER* / orbits.

Friday, 22 July 1994

    12:33 AM                        Con't. mapping
				    of Jupiter (WFPC)

     3:53 AM                        *W IMPACTS JUPITER*

     8:36 AM                        Spectroscopic search for SiO 
                                    in Jupiter's atmosphere; 
				    2 orbits (HRS)

     9:30 AM			    Press Briefing at GSFC


Saturday, 23 July 1994

     2:18 AM                        6-orbit mapping
				    sequence of Jupiter (WFPC)

     8:00 AM			    Press Briefing at GSFC

     9:00 AM                        Press Briefing at STScI

Sunday, 24 July 1994

     2:25 AM                        Spectroscopic obser-
                                    vations of Io torus;
                                    5-orbits (HRS)

    12:04 PM                        Observations of Io
				    torus; 1-orbit (HRS)

The nominal end of the HST Jupiter campaign is 24 August 1994. In the
intervening month, further spectroscopic observations of the Io plasma
torus, UV imaging of Jupiter, post-impact WFPC mapping of Jupiter, and
spectroscopy of Jupiter itself will continue. 

Note:  The press conference times are dependent on the STS-65 mission
schedule.  If there is a change in the launch or landing time of the
Shuttle, the program times will change. 

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Thu, 7 Jul 1994 18:33:05 -0400
% Errors-To: [email protected]
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: Robert Landis <[email protected]>
% To: Multiple recipients of list <[email protected]>
% Subject: Abbreviated HST Mission/Comet Impact Timeline
% X-Listprocessor-Version: 6.0 -- ListProcessor by Anastasios Kotsikonas

From:	US4RMC::"ASTRO%[email protected]" "Astronomy Discussion 
        List"  8-JUL-1994 13:14:38.89
To:	Multiple recipients of list ASTRO <ASTRO%[email protected]>
CC:	
Subj:	New Hubble Images of Comet Shoemaker-Levy Available

Donald Savage
Headquarters, Washington, D.C.
July 7, 1994
(Phone:  202/358-1547)

NEW HUBBLE IMAGES OF COMET SHOEMAKER-LEVY 9 AVAILABLE

        Three recent images of Comet P/Shoemaker-Levy 9 and
Jupiter taken by NASA's Hubble Space Telescope are available
to news media representatives.

        The first image is a "true color" picture of the planet
Jupiter in detail surpassed only by images from spacecraft
which traveled to the planet.  The photo numbers are:
color:  94-HC-171       B&W:  94-H-185

        The second image is the latest of Comet P/Shoemaker-Levy
9, taken on May 17, 1994, showing the train of 21 fragments
stretched across 710 thousand miles of space.  TThe photo
numbers are:    color:  94-HC-172       B&W:  94-H-186

        The third image is a photo illustration assembled from
separate images of Jupiter and Comet P/Shoemaker-Levy 9,
showing the planet and comet in close proximity as it should
appear shortly before the comet fragments begin impacting the
giant planet July 16.  One by one, the comet fragments will
impact Jupiter during the week of July 16-22.  The photo
numbers are:       color:  94-HC-170       B&W:  94-H-184

        The first fragment, one of the smallest  of the comet's
fragments, will impact Jupiter just before 4 p.m. EDT, July
16, on the side of Jupiter facing away from Earth.  Shortly
afterwards, the point of impact will rotate into view as seen
from Earth.

        Because of its small size, most scientists do not expect
to witness significant visible effects from the impact of the
first fragment, nor to detect significant aftereffects in the
planet's atmosphere.  However, there is a greater possibility
of detectable effects resulting from the impacts of larger
fragments later during the week.  Some of the effects
scientists will be looking for in the Jovian atmosphere are
small changes in cloud structure as well as small changes in
the temperature structure, which can be measured using
infrared telescopes.

        Media representatives can obtain the images by calling
the NASA Headquarters Broadcast and Imaging Branch at 202/358-
1900.  Also, an updated listing of the comet fragment impact
times and viewing locations is available by contacting the
Newsroom at 202/358-1600.

- end -

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date:         Fri, 8 Jul 1994 16:56:20 +0000
% Reply-To: Astronomy Discussion List <ASTRO%[email protected]>
% Sender: Astronomy Discussion List <ASTRO%[email protected]>
% From: Ron Baalke <[email protected]>
% Subject:      New Hubble Images of Comet Shoemaker-Levy Available
% X-To:         [email protected]
% To: Multiple recipients of list ASTRO <ASTRO%[email protected]>


From:	US4RMC::"ASTRO%[email protected]" "Astronomy Discussion 
        List"  8-JUL-1994 13:22:33.80
To:	Multiple recipients of list ASTRO <ASTRO%[email protected]>
CC:	
Subj:	JPL Comet-Jupiter Collision Briefing

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109.  TELEPHONE (818) 354-5011

Contact:  James H. Wilson

NOTE TO EDITORS AND NEWS DIRECTORS                      July 8, 1994

     The latest update from astronomers on the upcoming collision
of a comet with the giant planet Jupiter will be available to Los
Angeles area news media at a special briefing Monday, July 11, at
the Jet Propulsion Laboratory.

     New animation video footage will also be available at the
briefing, which begins at 11:30 a.m. in von Karman Auditorium at
JPL, 4800 Oak Grove Drive, Pasadena.

     Main speaker will be Dr. Donald Yeomans, JPL astronomer and
comet expert, whose team calculates the times and places that
fragments of Comet Shoemaker-Levy 9 will slam into Jupiter
between July 16 and 22.  Called the "string-of-pearls" comet, the
celestial object is already torn apart and is speeding through
space as a long trail of fragments that will hit the solar
system's largest planet over a seven-day period.

     Joining Yeomans at the briefing will be representatives of
JPL's Galileo, Ulysses and Voyager spacecraft -- all of which
will observe the comet collisions from their vantage points in
space -- and a representative of the JPL-built camera on the
Hubble Space Telescope, which will also record the once-in-a-
lifetime event.

     For more information, journalists may call JPL's Public
Information Office at (818) 354-5011.

                            #####

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% Date:         Fri, 8 Jul 1994 16:50:40 +0000
% Reply-To: Astronomy Discussion List <ASTRO%[email protected]>
% Sender: Astronomy Discussion List <ASTRO%[email protected]>
% From: Ron Baalke <[email protected]>
% Subject:      JPL Comet-Jupiter Collision Briefing
% X-To:         [email protected]
% To: Multiple recipients of list ASTRO <ASTRO%[email protected]>

From:	US4RMC::"ASTRO%[email protected]" "Astronomy Discussion 
        List" 11-JUL-1994 16:57:47.15
To:	Multiple recipients of list ASTRO <ASTRO%[email protected]>
CC:	
Subj:	Latest Galileo Imaging Plans for Comet Shoemaker-Levy

                           M E M O R A N D U M

To:         SL-9 Observers

From:       Clark R. Chapman
            Planetary Science Inst./SAIC
            620 N. 6th Ave.
            Tucson, AZ  85705  USA
                  [Phone: 602-622-6300; FAX: 602-622-8060]
                  [E-mail: [email protected]]

Date:       8 July 1994

Subject:    Galileo Imaging Plans

      The Galileo sequence that contains the observations of Comet
SL-9's impact with Jupiter has been completed, approved, and
transmitted to the spacecraft, according to the cognizant JPL
specialist, Catherine Heffernan. The July 5th updates by Chodas and
Yeomans were used to develop "tweaks" to the times that we will be
recording data to tape.  (The shutter will be operated for about 2
hours around each of the 6 events we are observing, but only about one
hour of data will be recorded on tape for each event...the tweaks have
updated the record times from those we estimated earlier.) 

      The table below gives impact times and observation times for the
6 events that will be imaged by the camera, and indicates the type of
observation (we are using 4 different modes). 

All times are in Spacecraft Event Time -- UTC (these are EARLIER than
times observed on Earth!).

Fragment, type            impact time      1 sigma       observation time
                                            (min)        start     stop
------------------------  ----------       -------       ----------------
D, 8x8 start/stop mosaic  7/17 11:12:27      8.7         10:45     11:48
   8 2/3-second imaging

E, 8x8 start/stop mosaic  7/17 14:34:26      8.0         14:05     15:08
   8 2/3-second imaging

K, diagonal slew          7/19 09:48:17      6.5          9:21     10:24
   30 1/3-sec imaging

N, diagonal slew          7/20 09:48:47      8.6          9:26     10:29
   30 1/3-sec imaging

V, horizontal slew        7/22 03:27:20     12.4          2:54      3:57
   30 1/3-sec imaging

W, 8x8 continuous slew    7/22 07:23:09      9.1          6:51      7:55
   mosaic, 2 1/3-second
   imaging

      By July 22nd, the imaging team must deliver to the Galileo
Project the starting point for a jailbar search for events D, E, K,
and N.  This will depend critically on information downlinked by the
Galileo PPR instrument for events B, H, and L and on ANY AND ALL
INDICATIONS FROM GROUNDBASED OBSERVERS ABOUT WHEN IMPACT AND OTHER
OPTICALLY IMPORTANT PHENOMENA ASSOCIATED WITH EVENTS D, E, K, AND N
(and later for V and W) MAY HAVE OCCURRED.  The first jailbar data
will be downlinked and analyzed by the first few days in August, on
the basis of which we will uplink the parameters to acquire the
75-line swaths of data from event D.  A similar process continues
through August and September for the other impacts we observed.  It is
anticipated that we will receive our first real data by about mid-August. 

      We are optimistic that we can detect the impacts of SL-9
fragments, even if the comet has "fizzled" (from the perspective of
Earth-based observers) into a meteor storm.  Naturally, we hope for
the complete range of bolide and fireball phenomena that may shed the
maximum amount of light on Jupiter's chemistry, atmospheric dynamics,
and so on. 

      I have been leading the imaging team's SL-9 science
investigation. The other cognizant members of the imaging team are
Team Leader Mike Belton, Andy Ingersoll, and Joe Veverka.  We would
welcome comments and questions from our colleagues...and any reliable
information that you have that will help narrow our uncertainties about 
where we are most likely to find our direct imaging of the impact sites 
on our tape recorder (i.e. impact times for D, E, K, N, V, and W). 

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date:         Mon, 11 Jul 1994 17:15:23 +0000
% Reply-To: Astronomy Discussion List <ASTRO%[email protected]>
% Sender: Astronomy Discussion List <ASTRO%[email protected]>
% From: Ron Baalke <[email protected]>
% Subject:      Latest Galileo Imaging Plans for Comet Shoemaker-Levy
% X-To:         [email protected]
% To: Multiple recipients of list ASTRO <ASTRO%[email protected]>

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 12-JUL-1994 18:22:14.89
CC:	
Subj:	Comet/Jupiter Collision FAQ

    This will probably be the last FAQ update until after the collisions.  
The PostScript version has been uploaded to seds.lpl.arizona.edu
and tamsun.tamu.edu.  The programs GALSAT53 and TRACKER3 that are 
mentioned below will be updated again by July 15th.  Clear skies.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

                      Frequently Asked Questions about
            the Collision of Comet Shoemaker-Levy 9 with Jupiter

                         Last Updated 12-July-1994
                             4 Days to Impact
                                           
      Contact Dan Bruton ([email protected]) or John Harper ([email protected]) 
with comments, additions, corrections, etc.  A PostScript version of this 
FAQ list is available at tamsun.tamu.edu (128.194.15.32) in the /pub/comet 
directory.  To subscribe to the "Comet/Jupiter Collision Mailing List", send 
mail to [email protected] (no subject) with the message: 
SUBSCRIBE SL9 Firstname Lastname
            
RECENT CHANGES TO THIS FAQ LIST

        Question 2.1: Impact times as of July 11, 1994, missing fragments,
                      and likelihood of fireball visibility
        Question 2.6: Fragment sizes       
        Question 2.10: New WWW sites 

GENERAL QUESTIONS

 Q1.1: Is it true that a comet will collide with Jupiter in July 1994?
 Q1.2: Who are Shoemaker and Levy?
 Q1.3: Where can I find a GIF image of this comet?
 Q1.4: What will be the effects of the collision?
 Q1.5: Can I see the effects with my telescope?
 Q1.6: Will there be live TV coverage of the events?

SPECIFICS

 Q2.1: What are the impact times and impact locations?
 Q2.2: Can the collisions be observed with radio telescopes? 
 Q2.3: Will light from the explosions be reflected by any moons? 
 Q2.4: What are the orbital parameters of the comet? 
 Q2.5: Why did the comet break apart? 
 Q2.6: What are the sizes of the fragments? 
 Q2.7: How long is the fragment train? 
 Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions? 
 Q2.9: To whom can I report my observations? 
 Q2.10: Where can I find more information?

REFERENCES
ACKNOWLEDGMENTS

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

GENERAL QUESTIONS

Q1.1: Is it true that a comet will collide with Jupiter in July 1994?

     Yes, the shattered comet Shoemaker-Levy 9 will collide with Jupiter over 
a 5.6 day period in July 1994.  The first of 21 comet fragments is expected 
to hit Jupiter on July 16, 1994 and the last on July 22, 1994.  The 21 major 
fragments are denoted A through W in order of impact, with letters I and O 
not used.  All of the comet fragments will hit on the dark farside of Jupiter.  
The probability that all of the comet fragments will hit Jupiter is greater 
that 99.9%.  The probability that any fragment will impact on the near side 
as viewed from the Earth is < 0.01%.
     The impact of the center of the comet train is predicted to occur at a
Jupiter latitude of about -44 degrees at a point about 67 degrees east 
(toward the sunrise terminator) from the midnight meridian.  These impact 
point estimates from Chodas and Yeomans are only 5 to 9 degrees behind the 
limb of Jupiter as seen from Earth.  About 8 to 18 minutes after each 
fragment hits, the impact points will rotate past the limb.  After these 
points cross the limb it will take another 18 minutes before they cross the 
morning terminator into sunlight.                        


Q1.2: Who are Shoemaker and Levy?

   Comet Shoemaker-Levy 9 (1993e) was the ninth short-period comet discovered 
by Eugene and Carolyn Shoemaker and David H. Levy and was first identified on 
photographs taken on the night of 24 March 1993.   The photographs were taken 
at Palomar Mountain in Southern California with a 0.46 meter Schmidt camera 
and were examined using a stereomicroscope to reveal the comet [2,14].  The 
13.8 magnitude comet appeared 'squashed' in the original image.  Subsequent 
photographs taken by Jim Scotti with the Spacewatch telescope on Kitt Peak 
in Arizona showed that the comet was actually a shattered comet.  Some
astronomers call the comet a "string of pearls" since the comet fragments
are strung out in a line or train.
    Before the end of March 1993 it was realized that the comet had made a very
close approach to Jupiter in the summer of 1992.  At the beginning of April 
1993, after sufficient observations had been made to determine the orbit more 
reliably, Brian Marsden found that the comet is in orbit around Jupiter.  By 
late May 1993 it appeared that the comet was likely to impact Jupiter in 1994.  
Since then, the comet has been the subject of intensive study.  Searches of 
archival photographs have identified pre-discovery images of the comet from 
earlier in March 1993 but searches for even earlier images have been 
unsuccessful.  See [11] for more information about the discovery.


Q1.3: Where can I find a GIF image of this comet?

     GIF images can be obtained from SEDS.LPL.Arizona.EDU (128.196.64.66)
in the /pub/astro/SL9/images directory.  Below is a list of the images at
this site.  The files are listed here in reverse chronological order:

Comet1993eA.gif    March HST image of SL9 comet train
Comet1993eB.gif    Time comparison image of SL9 comet fragment
sl90216.gif        February 16, 1994 Image from Kitt Peak (J. Scotti)
wfpclevy.gif       Photo Montage of January 24-27 Imaging of SL9 from HST
sl9hst.gif         Post-fix HST Mosaic of SL9 (Jan. 24-27)
sl90121.gif        January 21, 1994 Image from Kitt Peak (R. Jedicke)
sl9compl.gif       Six month comparison image of SL9
1993eha.gif        View of the comet from HST
1993ehb.gif        From HST, focused on the center of the train of fragments
1993esw.gif        Ground-based view of the comet
sl03302b.gif       March 30, 1993 Image from Kitt Peak (J. Scotti)
sl9_930330.gif     March 30, 1993 image of SL9, Spacewatch, J. Scotti
sl9w_930328.gif    March 28, 1993 image of SL9
shoelevy.gif       An early GIF image of SL9
                                     
There are also other collision related GIF graphics and MPEG animations 
at SEDS.LPL.Arizona.EDU.  See Question 2.10 for other FTP and WWW sites.
Most of these sites will have images of Jupiter after the collisions.


Q1.4: What will be the effects of the collision?

     Jupiter will be about 770 million kilometers (480,000,000 miles) from
Earth, so it will be difficult to see the effects from Earth.  Also, 
the comet fragments will not effect Jupiter as a whole very much.  It will 
be like sticking 21 needles into an apple: "Locally, each needle does 
significant damage but the whole apple isn't really modified very much." [35].
The energy deposited by the comet fragments fall well short of the energy 
required to set off sustained thermonuclear fusion.  Jupiter would have to 
be more than 10 times more massive to sustain a fusion reaction.  
     Calculations by Paul Chodas (JPL) indicate that as seen from the Earth, 
the fragments will disappear behind the limb of Jupiter only 5 to 15 seconds 
before impact.  The later fragments will be visible closer to impact.  
Fragment W will disappear only 5 seconds before impact, at an altitude of only
about 200 km above the 1-bar pressure level: it may well start its bolide 
phase while still in view.  Furthermore, any sufficiently dense post-impact 
plume will have to rise only a few hundred kilometers to be visible from Earth.
     Simulations for 2-4 km fragments by Mark Boslough (Sandia National
Laboratories) indicate when the fireball resulting from an impact cools it 
would form a debris cloud that will rise hundreds of kilometers above the 
Jovian cloudtops, and would enter sunlight within minutes of the impact.  The 
arrival time of this giant cloud into sunlight would provide data on its 
trajectory, which in turn would help us know how big the comet fragment was.  
It is possible that it would be big (bright) enough to be seen by amateurs 
[42,43].  
     If the fragments are 2-4 km in diameter then the probability is very high
that these effects will be visible for some of the later impacts (e.g. W and R,
visible from Hawaii, S, visible from India and the far East, Q1 and Q2, visible
from Africa, parts of eastern Europe and the Middle East, L, Brazil and West 
Africa, K, South Pacific and Australia, and maybe even V, on the final night, 
visible in the Western half of the U.S.).  Observers in these locations are 
encouraged to anticipate the possibility of seeing the fireball within tens of
seconds after the impact, and a few minutes later after it has cooled, 
condensed, and entered the sunlight.  The apparent visible magnitude of any 
fireball will be similar to that of a Galilean satellite at best, but it would
appear redder.  They would be much brighter at infrared wavelengths.
     The following predictions by Mordecai-Mark Mac Low (University of Chicago)
are based on simulations for 1 km fragments:  Each comet fragment will enter
the Jupiter's atmosphere at a speed of 130,000 mph (60 km/s).  At an altitude 
of 100 km above the visible cloud decks, aerodynamic forces will overwhelm the
material strength of the fragment and tear it apart.  Five seconds after 
entry, the comet fragment would deposit its kinetic energy of around 10^28 ergs
(equivalent to around 200,000 megatons of TNT) at 100-150 km below the cloud 
layer [19].  Bigger fragments will have more energy and go deeper.
     The hot (30,000 K) gas resulting from a 1 km stopped comet will explode,
forming a fireball similar to a nuclear explosion, but much larger.  The 
visible fireball may only rise 100 km or so above the cloudtops in this case.
Above that height the density may drop so that it will become transparent.  
The fireball material will continue to rise, reaching a height of perhaps 
1000 km before falling back down to 300 km.  The fireball will spread out over
the top of the stratosphere to a radius of 2000-3000 km from the point of 
impact.  The top of the resulting shock wave will accelerate up out of the 
Jovian atmosphere in less than two minutes, while the fireball will be as 
bright as the entire sunlit surface of Jupiter for around 45 sec [18].  The 
fireball will be somewhat red, with a characteristic temperature of 2000 K - 
4000 K (redder than the sun, which is 5800 K).  Virtually all of the shocked 
cometary material will rise behind the shock wave, leaving the Jovian 
atmosphere and then splashing back down on top of the stratosphere at an 
altitude of 300 km above the clouds [unpublished simulations by Mac Low & 
Zahnle].  Not much mass is involved in this splash, so it will not be directly
observable.  The splash will be heavily enriched with cometary volatiles such 
as water or ammonia, and so may contribute to significant high hazes.
        Meanwhile, the downward moving shock wave will heat the local clouds,
causing them to buoyantly rise up into the stratosphere.  This will allow
spectroscopists to attempt to directly study cloud material, a unique
opportunity to confirm theories of the composition of the Jovian clouds.
Furthermore, the downward moving shock may drive seismic waves (similar to
those from terrestrial earthquakes) that might be detected over much of the
planet by infrared telescopes in the first hour or two after each impact.
The strength of these two effects remains a topic of research.  The
disturbance of the atmosphere will drive internal gravity waves ("ripples in
a pond") outwards.  Over the days following the impact, these waves will
travel over much of the planet, yielding information on the structure of
the atmosphere if they can be observed (as yet an open question).
     The "wings" of the comet will interact with the planet before and after
the collision of the major fragments.  The so-called "wings" are defined to
be the distinct boundary along the lines extending in both directions from 
the line of the major fragments; some call these 'trails'.  Sekanina, Chodas
and Yeomans have shown that the trails consist of larger debris, not dust: 
5-cm rock-sized material and bigger (boulder-sized and building-sized).  
Dust gets swept back above (north) of the trail-fragment line due to solar 
radiation pressure.  The tails emanating from the major fragments consist of
dust being swept in this manner.  Only the small portion of the eastern 
debris trail nearest the main fragments will actually impact Jupiter, 
according to the model, with impacts starting only a week before the major 
impacts (July 8, 1994).  The western debris trail, on the other hand, will 
impact Jupiter over a period of months following the main impacts, with the 
latter portion of the trail actually impacting on the front side of Jupiter 
as viewed from Earth [20].
     The injection of dust from the wings and tail into the Jovian system
may have several consequences.  First, the dust will absorb many of the
energetic particles that currently produce radio emissions in the Jovian
magnetosphere.  The expected decline and recovery of the radio emission may
occur over as long as several years, and yield information on the nature and
origin of the energetic particles.  Second, the dust may actually form a
second faint ring around the planet.
     At the University of Oregon astronomers plan to monitor the linearly and 
circular polarized light from Jupiter.  They have a sensitive detector that 
can detect changes of one part in 10^5 and they expect to see some kind of 
change in the polarization signal as the magnetic field of Jupiter is 
disrupted by the impacts.
     Due to the great distance between Jupiter and the Earth, the comet 
poses no threat to Earth.  However, Eugene Shoemaker says that if a similar 
comet crashed on Earth it would be catastrophic:  "...we're talking about a 
million megatons of kinetic energy.  We're talking about the kind of event 
that is associated with mass extinction of species on Earth; really and truly 
a global catastrophe.  It might not take out the human race but it would 
certainly be very bad times." (CNN, Headline News)


Q1.5: Can I see the effects with my telescope?

     One might be able to detect atmospheric changes on Jupiter using
photography or CCD imaging.  It is important, however, to observe Jupiter
for several months in advance in order to know which features are due to
impacts and which are naturally occurring.  It appears more and more likely
that most effects will be quite subtle.  Without a large ( > 15" ?) telescope
and good detector, little is likely to be seen.
     It is possible that the impacts may create a new, temporary storm at the
latitude of the impacts.  Modeling by Harrington et al. suggests this is
possible [30].  The fragments of comet Shoemaker-Levy 9 will strike just
south of the South South Temperate Belt of Jupiter.  If the nuclei penetrate 
deep enough, water vapor may shoot high into the atmosphere where it could 
turn into a bluish shroud over a portion of the South South Temperate Zone 
[31].
     Impacts of the largest fragments may create one or two features.  A spot
might develop that could be a white or dark blue nodule and would likely have
a maximum diameter of 2,000 km to 2,500 km which in a telescope would be 1
to 1.5 arcseconds across.  This feature would be very short-lived with the
impact site probably returning to normal after just a few rotations of 
Jupiter.  A plume might also develop that would look dark against the South
Temperate Zone's white clouds or could appear as a bright jet projected from
Jupiter limb [31].  The table below shows the approximate sizes of features
that already exist on Jupiter for comparison.

 +==================================================================+ 
 |          FEATURE                            SIZE ESTIMATES       | 
 +==================================================================+
 |       Great Red Spot                       26000 by 11000 km     |
 |     White Spots FA,BC,DE                   9000 km               |
 |  Shadows of Io, Europa, and Ganymede       4300, 4200, 7100 km   |
 +==================================================================+

     Below is a list of files available at tamsun.tamu.edu in the /pub/comet
directory that may be helpful in identifying features on Jupiter:

tracker3.zip      MSDOS program that displays the location of impact sites
                  and features of Jupiter
jupe.description  Description of a PC program showing features of Jupiter
jul1994.transit   Transit Times for Red Spot and White Spots for July 1994
jul1994.moons     Jovian Moon events for July 1994 (Shadows, Eclipses, etc.)

    Also, there are little anticyclonic ovals at jovicentric latitudes of 
about -45 degrees which are typical of the South South Temperate domain
and are about 3500 km in diameter.  There are usually 6 or 7 around the planet
and they move with the South South Temperate current, i.e. faster than BC and 
DE.  See Sky & Telescope for a CCD image of these ovals by Don Parker [38].


Q1.6: Will there be live TV coverage of the events?

        NASA's coverage of the impact of Comet P/Shoemaker-Levy 9 during 
the week of July 16-22 includes a series of live, televised press briefings 
and a 24-hour newsroom operation at the Goddard Space Flight Center (GSFC), 
Greenbelt, Md.  The briefing panels will include Comet co-discoverers Drs. 
Eugene and Carolyn Shoemaker and David Levy on most days as well as scientists
presenting images and information from the Hubble Space Telescope and other 
spacecraft.  Dr. Lucy McFadden will have a round-up of observations from 
ground-based observatories around the world.  The program and briefing 
schedule follows:

JULY DATE       TIME (EDT)      EVENT
Sat.    16      10:00 p.m.      Live from HST: First Impact Image Release
Sun.    17      8:00 a.m.       Press Briefing at GSFC
Mon.    18      8:00 a.m.       Press Briefing at GSFC
Tue.    19      8:00 a.m.       Press Briefing at GSFC
Wed.    20      12:00 noon      Press Briefing at GSFC
Th.     21      8:00 a.m.       Press Briefing at GSFC
Fri.    22      9:30 a.m.       Press Briefing at GSFC
Sat.    23      8:00 a.m.       Press Briefing at GSFC
                                                     
Note:  The above times are dependent on the STS-65 mission schedule.  If 
there is a change in the launch or landing time of the Shuttle, the program 
times will change.  Video Uplink Schedule: NASA will provide feeds of b-roll 
and animation of the comet impacts with Jupiter on the following schedule:
July 15, 1:00 p.m. EDT.  NASA TV is carried on Spacenet 2, transponder 5, 
channel 9, 69 degrees West, transponder frequency is 3880 MHz, audio 
subcarrier is 6.8 MHz, polarization is horizontal.
     CNN also plans to offer live coverage at 10:00pm EDT on July 16th with 
comments and explanation from scientists at Goddard and the Space Telescope 
Science Institute.  CNN plans live coverage of at least the first 2 briefings 
(Sunday and Monday) and then TBA depending on what the images look like.  CNN 
also plans to have live reports at 9am and noon EDT throughout the week with a 
daily comet report for release in the afternoon.
     Note also that your local PBS station will normally pick up one 
of the live feeds listed below so that you will see it at 10:30-11:30 
local time.  If you have a TVRO satellite dish you can watch it 5 times.

PBS : "THE GREAT COMET CRASH"
Wednesday July 20, 1994   (into early Thursday morning 7/21)
10:30pm - 11:30pm     Telstar 401-Ku 6 (PBS Schedule B)
11:30pm - 12:30am     Telstar 401-Ku 6 (PBS Schedule B)
12:30am - 1:30 am     Telstar 401-Ku 6 (PBS Schedule B)
 1:30am - 2:30 am     Telstar 401-Ku 7 (PBS Schedule C)
 2:30am - 3:30 am     Telstar 401-Ku 5 (PBS Schedule A)
 2:30am - 3:30 am     Telstar 401-C band 8 (PBS Schedule X)
                                                                 
    Also, there is a gathering of professional and amateur astronomers every 
week on the IRC (Internet Relay chat) channel #Astronomy for real time 
discussions.  Friday and Sunday sessions are held at 20:00 UT.  There may be 
continuous discussion/updates on the IRC channel #Astronomy during the impacts.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

SPECIFICS

Q2.1: What are the impact times and impact locations?

This information was provided P.W. Chodas and D.K. Yeomans:
==============================================================================

  Predicted Impact Parameters for Fragments of P/Shoemaker-Levy 9
  ---------------------------------------------------------------

  P.W. Chodas, D.K. Yeomans and Z. Sekanina (JPL/Caltech)
  P.D. Nicholson (Cornell)

  Predictions as of 1994 July 11
  Date of last astrometric data in these solutions: 1994 July 10

The predictions for all fragments except Q2 are based on independent orbit
solutions; our orbit reference identifier is given.  The orbit solution
for fragment Q2 was obtained by applying a disruption model to the orbit
for Q1, and using astrometric measurements of Q2 relative to Q1.

Except for fragment Q2, uncertainties in the impact parameters are given
immediately below the predicted values.  These uncertainties are 1-sigma
values obtained from Monte Carlo analyses; we have made an effort to make
them realistic: they are not formal uncertainty values.  NOTE: To obtain a
95% confidence level, one should use a +/- 2 sigma window around the
predicted values.  The uncertainties for Q2 have not been quantified, but
are probably comparable to those for fragment T.

The dynamical model used for these predictions includes perturbations due to
the Sun, planets, Galilean satellites and the oblateness of Jupiter.  The
planetary ephemeris used was iDE245.

-------------------------------------------------------------------------------
Frag-    Impact       Jovicentric  Merid.  Angle          Satellite Longitudes
  ment  Date/Time     Lat.  Long.  Angle   E-J-F  Orbit     at Impact  (deg)
       July  (UTC)    (deg) (deg)  (deg)   (deg)   Ref.  Amal   Io   Eur   Gany
------------h--m--s------------------------------------------------------------
A = 21  16 19:57:34  -43.11  177   64.28   98.87   A20   205   345   107+   77+
               8.2      .19    5     .76     .56           4     1     1     0
B = 20  17 02:54:02  -43.15   70   63.78   99.21   B19    55+   43+  136+   91+
               6.8      .20    4     .75     .56           3     1     0     0
C = 19  17 06:59:25  -43.31  217   65.05   98.27   C16   177t   77+  153+  100+
               7.0      .17    4     .74     .55           4     1     0     0
D = 18  17 11:45:30  -43.40   29   65.47   97.95   D17   321   118+  173   11+
               7.5      .18    4     .77     .57           4     1     1     0
E = 17  17 15:05:00  -43.45  149   65.78   97.71   E33    61+  146+  187   117+
               5.6      .08    3     .46     .33           3     1     0     0
F = 16  18 00:26:39  -43.52  130   64.40   98.67   F24   343o  226   226   136+
               6.0      .12    4     .57     .41           3     1     0     0
G = 15  18 07:27:36  -43.58   23   66.58   97.10   G31   194t  286   255   151+
               4.8      .07    3     .38     .27           2     1     0     0
H = 14  18 19:25:55  -43.72   96   66.85   96.88   H30   194t   27+  305   176
               4.7      .07    3     .38     .27           2     1     0     0
K = 12  19 10:17:50  -43.79  275   67.72   96.24   K32   282   152+    8+e 207
               4.8      .07    3     .40     .28           2     1     0     0
L = 11  19 22:07:07  -43.90  343   68.09   95.95   L32   278   253    59+  232
               5.1      .07    3     .39     .28           3     1     0     0
N = 9   20 10:21:15  -44.27   67   67.87   96.03   N21   286   357o  112+  257
               6.7      .12    4     .68     .48           3     1     0     0
P2= 8b  20 15:09:51  -44.59  243   66.57   96.88   P19    71+   37+  132+  268
               6.6      .09    4     .59     .41           3     1     0     0
Q2= 7b  20 19:32:02  -44.34   39   68.83   95.33         202t   74+  150+  277
                                                           8     2     1     1
Q1= 7a  20 19:59:29  -44.04   55   69.25   95.08   Q35   216    78+  152+  278
               5.4      .07    3     .41     .29           3     1     0     0
R = 6   21 05:24:17  -44.07   36   69.35   95.00   R30   139   157   191   297
               6.2      .08    4     .47     .33           3     1     0     0
S = 5   21 15:09:53  -44.16   30   69.78   94.69   S41    74+  241   232   318
               5.9      .08    4     .42     .29           3     1     0     0
T = 4   21 18:05:50  -45.00  139   67.44   96.18   T14   161t  266   244   324
              13.2      .16    8    1.00     .70           7     2     1     0
U = 3   21 21:52:39  -44.45  274   68.98   95.20   U15   276   298   260   332
              14.5      .19    9    1.13     .79           7     2     1     1
V = 2   22 04:14:43  -44.41  145   69.32   94.96   V16   107+  352o  286   345
              10.3      .16    6    1.00     .71           5     1     1     0
W = 1   22 07:56:53  -44.16  278   70.38   94.25   W32   218    23+  302   353
               7.2      .10    4     .53     .37           4     1     1     0

Satellite Codes:  +  impact is visible from satellite
                  o  satellite is occulted by Jupiter at impact
                  e  satellite is eclipsed but not occulted at impact
                  t  satellite is in transit across Jupiter
-------------------------------------------------------------------------------

Notes:
1. Fragments J=13, M=10, and P1=8a are omitted because they have faded from
   view.  The March'94 HST images show that P2=8b and G=15 have split; we do
   not have sufficient data to obtain independent predictions for the
   sub-components.

2. The impact date/time is the time the impact would be seen at the Earth
   (if the limb of Jupiter were not in the way); the date is the day in
   July 1994; the time is given as hours and minutes of Universal Time.
   The impact time uncertainty is a 1-sigma value in minutes.

3. The impact latitude is Jovicentric (latitude measured at the center of
   Jupiter); the Jovigraphic latitudes are about 3.84 deg more negative.

4. The impact longitude is System III, measured westwards on the planet. The
   large uncertainty in impact longitudes is due to Jupiter's fast rotation.

5. The meridian angle is the Jovicentric longitude of impact measured from
   the midnight meridian towards the morning terminator.  This relative
   longitude is known much more accurately than the absolute longitude.
   At the latitude of the impacts, the Earth limb is at meridian angle 76 deg
   and the terminator is at meridian angle 87 deg.

6. Angle E-J-F is the Earth-Jupiter-Fragment angle at impact; values greater
   than 90 deg indicate a farside impact.  All impacts will be just on the
   farside as viewed from Earth; later impacts will be closer to the limb.

7. Satellite longitudes are given for Amalthea, Io, Europa, and Ganymede.
   The longitudes are measured east from superior conjunction (the anti-Earth
   direction).  Longitude uncertainties listed as "0" are simply < 0.5 deg.

8. According to these predictions, the only impact certain to occur during a
   satellite eclipse is K=12 with Europa eclipsed.

Since the discovery of Comet Shoemaker-Levy 9, some of the fragments of have
disappeared from view.  These were probably smaller fragments to begin with,
and they have probably disintegrated further, but some sizable pieces may
remain amongst the debris at these locations in the train.  We have computed
approximate impact times for three of these missing fragments, based on the
few available positional measurements, and using our tidal disruption model:

  Fragment    Impact      Last Seen
             Date/Time
             July (UTC)
  ----------------h--m-----------------
   J = 13    19  02:40    Dec. 1993
   M = 10    20  05:45    July 1993
   P1= 8a    20  16:30    Mar. 1994

The uncertainties on these impact times are large: probably about 60 min.,
1-sigma.  The impact locations are consistent with those of the other
fragments, i.e., at jovicentric latitude -44 and well behind the limb of
Jupiter as seen from the Earth.

[Courtesy of Paul Chodas, JPL]

==============================================================================
     
     The angle of incidence of the impacts is between 41 and 42 degrees for 
all the fragments.   See "impacts.*" at SEDS.LPL.Arizona.EDU in the 
/pub/astro/SL9/info directory for updates.  The following are the 1-sigma 
(uncertainty) predictions for the fragment impact times:

               on March 1         -  30 min
               on May 1           -  24 min
               on June 1          -  16 min
               on July 1          -  10 min
               on July 15         -   6 min
               at impact - 18 hr  -   3 min

The time between impacts is thought to be known with more certainty than the
actual impact times.  This means that if somehow the impact time of the first
fragment can be measured experimentally, then impact times of the fragments
that follow can be predicted with more accuracy.

Relative Likelihood of Fireball Visibility for Fragments of Shoemaker-Levy 9
-----------------------------------------------------------------------------
Mark Boslough and David Crawford (Sandia National Labs, Albuquerque, NM)

--------------------------------------------------------------------------
Fragment          Best Locations for Viewing            Likelihood of 
                   Jupiter at Impact Time            Visible Fireball (*)
--------------------------------------------------------------------------
   A              Africa (except W. Africa),                     :-(
                   Middle East, Eastern Europe           
   B              Eastern N. America, Mexico,                    :-(
                   Western S. America                    
   C              New Zealand, Hawaii                            :-(
   D              Australia, New Zealand,                        :-(
                   Japan                                 
   E              India, Southern China,                         :-|
                   S.E. Asia, Western Australia          
   F              S. America                                     :-|
   G              New Zealand, Hawaii                            :-)
   H              Africa (except W. Africa),                     :-)
                   Middle East, Eastern Europe           
   K              Australia, New Zealand                     :-) :-)
   L              Brazil, W. Africa, Spain                   :-) :-)
   N              Australia, New Zealand                         :-|
   P2             India, Southern China,                         :-|
                   S.E. Asia, Western Australia          
   Q1             Africa (except W. Africa),             :-) :-) :-)
   Q2             Middle East, Eastern Europe                    :-)
   R              Hawaii, West coast N. America              :-) :-)
   S              India, Southern China,                 :-) :-) :-)
                   S.E. Asia, Western Australia          
   T              Africa (except W. Africa),                     :-(
                   Middle East, Eastern Europe           
   U              Brazil, W. Africa, Spain                       :-|
   V              Western U.S., Mexico                           :-|
   W              New Zealand, Hawaii,                   :-) :-) :-)
                   Eastern Australia                     
                                                       
 Key:  :-) :-) :-)   Best group (Most likely to be visible)
           :-) :-)       Second best group
               :-)           Third best group
               :-|              Not very good
               :-(                 Worst (Least likely to be visible)

(*) Based on the following sources:
       1) Ballistic fireball trajectories of
          M.B. Boslough, D.A. Crawford, A.C. Robinson and T.G. Trucano
          (Sandia National Laboratories)
         "Watching for Fireballs on Jupiter", EOS, July 5, 1994.
       2) Relative brightnesses of fragments from Karen Horrocks, May, 1994.
       3) Predicted impact locations in distance beyond Jupiter's limb by
          Chodas et al. (above).


Q2.2: Can the collision be observed with radio telescopes?

     The cutoff of radio emissions due to the entry of cometary dust into the
Jovian magnetosphere during the weeks around impact may be clear enough to be
detected by small radio telescopes.  Furthermore, impacts may be directly
detectable in radio frequencies.  Some suggest to listen in on 15-30 MHz 
during the comet impact.  So it appears that one could use the same antenna
for both the Jupiter/Io phenomenon and the Jupiter/comet impact.  There is 
an article in Sky & Telescope magazine which explains how to build a simple
antenna for observing the Jupiter/Io interaction [4,24,25].  
     For those interested in radio observations during the SL9 impact, 
Leonard Garcia of the University of Florida has made some information 
available.  The following files are available via anonymous ftp on the 
University of Florida, Department of Astronomy site astro.ufl.edu in the
/pub/jupiter directory:

  README.DOC      Explanation of predicted Jupiter radio storms tables
  jupradio.txt    Jovian Decametric Emission and the SL9/Jupiter Collision
  july94.txt      Tables of predicted Jupiter radio storms for July 1994

    The antenna required to observe Jupiter may be as simple as a dipole
antenna constructed with two pieces of wire 11 feet 8.4 inches in length,
connected to a 50 ohm coax cable.  This antenna should be laid out on a
East-West line and raised above the ground by at least seven feet.  A
Directional Discontinuity Ring Radiator (DDRR) antenna is also easy to
construct and can be made from 1/2 inch copper tubing 125.5 inches in
length (21Mhz).   The copper tube should be bent into a loop and placed 5
inches above a metallic screen.   A good preamp is required for
less sensitive shortwave receivers [39].
     Society of Amateur and Radio Astronomers (SARA) say that amateur radio 
astronomers may have to wait approximately three hours after impact for the
impact sites to rotate to the central meridian of Jupiter before anything 
unusual is detected.  This wait is typical due to the Jovian decametric 
synchrotron emissions being emitted as a beam of radiation.  Due to the 
large time differential from impact to radio observations any disturbance may 
have settled and not be detected.  SARA suggest that the radio observer 
begin the watch approximately 30 minutes before the fragments hit to four 
hour after.


Q2.3: Will light from the explosions be reflected by any moons?

     One may be able to witness the collisions indirectly by monitoring the
brightness of the Galilean moons that may be behind Jupiter as seen from
Earth.  One could monitor the moons using a photometer, a CCD camera.  However,
current calculations suggest that the brightenings may be as little as 0.05% 
of the sunlit brightness of the moon [18].  If a moon can be caught in eclipse
but visible from the earth during an impact, prospects will improve 
significantly.  According to current predictions, the only impact certain to 
occur during a satellite eclipse is K=12 with Europa eclipsed.  However, H=14 
and W=1 impact only about 2 sigma after Io emerges from eclipse at longitude 
20 deg, and B=20, E=17 and F=16 impact 0.5-2 sigma after Amalthea emerges from
eclipse at longitude 34 deg.  See also Q2.1 of this FAQ for satellite locations.
     The following files contain information concerning the reflection of 
light by Jupiter's moons and are available at SEDS.LPL.Arizona.EDU :
                                                            
galsat53.zip      MSDOS Program that Displays relative positions of
                      Jupiter's Moons during times of impact
impact_24apr.ps   PostScript Plot of impact times at satellite availability

     Also, monitoring the eclipses of the Galilean satellites after the
impacts may yield valuable scientific data with the moons serving as 
sensitive probes of any cometary dust in Jupiter's atmosphere.  The geometry
of the eclipses is such that the satellites pass through the shadow at 
roughly the same latitude as the predicted comet impacts.  There is an 
article in the first issue of CCD Astronomy involving these observations.  
The article says that if the dust were to obscure sunlight approximately 
120 kilometers above Jupiter's cloud tops, Io could be more that 3 percent 
(0.03 magnitudes) fainter than normal at mideclipse [40].


Q2.4: What are the orbital parameters of the comet?

     Comet Shoemaker-Levy 9 is actually in a temporary orbit of Jupiter, 
which is most unusual: comets usually just orbit the Sun.  Only two comets 
have ever been known to orbit a planet (Jupiter in both cases), and this was 
inferred in both cases by extrapolating their motion backwards to a time 
before they were discovered.  S-L 9 is the first comet observed while orbiting
a planet.  Shoemaker-Levy 9's previous closest approach to Jupiter (when it 
broke up) was on July 7, 1992; the distance from the center of Jupiter was 
about 96,000 km, or about 1.3 Jupiter radii.  The comet is thought to have 
reached apojove (farthest from Jupiter) on July 14, 1993 at a distance of 
about 0.33 Astronomical Units from Jupiter's center.  The orbit is very 
elliptical, with an eccentricity of over 0.998.  Computations by Paul Chodas, 
Zdenek Sekanina, and Don Yeomans, suggest that the comet has been orbiting 
Jupiter for 20 years or more, but these backward extrapolations of motion are 
highly uncertain.  See "elements.*" and "ephemeris.*" at SEDS.LPL.Arizona.EDU 
in /pub/astro/SL9/info for more information.
     In the abstract "The Orbit of Comet Shoemaker-Levy 9 about Jupiter"
by D.K. Yeomans and P.W. Chodas (1994, BAAS, 26, 1022), the elements
for the brightest fragment Q are listed.  These elements are Jovicentric
and for Epoch 1994Jul15 (J2000 ecliptic):

   1994 Periapses    Jul 20.7846           Arg. of periapses   43.47999
   Eccentricity      0.9987338             Long. of asc. node  290.87450
   Periapses dist.   34776.7 km            inclination         94.23333


Q2.5: Why did the comet break apart?

     The comet broke apart due to tidal forces on its closest approach to
Jupiter (perijove) on July 7, 1992 when it passed within the theoretical
Roche limit of Jupiter.  Shoemaker-Levy 9 is not the first comet observed
to break apart.  Comet West shattered in 1976 near the Sun [3].  Astronomers
believe that in 1886 Comet Brooks 2 was ripped apart by tidal forces near
Jupiter [2].  Several other comets have also been observed to have split 
[41].
     Furthermore, images of Callisto and Ganymede show crater chains which 
may have resulted from the impact of a shattered comet similar to Shoemaker-
Levy 9 [3,17].  The satellite with the best example of aligned craters is 
Callisto with 13 crater chains.  There are three crater chains on Ganymede.
These were first thought to be from basin ejecta; in other words secondary 
craters [27].  See SEDS.LPL.Arizona.edu in /pub/astro/SL9/images for images 
of crater chains (gipul.gif and chain.gif).
     There are also a few examples of crater chains on our Moon.  Jay Melosh
and Ewen Whitaker have identified 2 possible crater chains on the moon which
would be generated by near-Earth tidal breakup.  One is called the "Davy
chain" and it is very tiny but shows up as a small chain of craters aligned
back toward Ptolemaeus.  In near opposition images, it appears as a high
albedo line; in high phase angle images, you can see the craters themselves.
The second is between Almanon and Tacitus and is larger (comparable to the
Ganymede and Callisto chains in size and length).  There is an Apollo 11
image of a crater chain on the far side of the moon at SEDS.LPL.Arizona.edu
in /pub/astro/SL9/images (moonchain.gif).


Q2.6: What are the sizes of the fragments?

     Using measurements of the length of the train of fragments and a model
for the tidal disruption, J.V. Scotti and H.J. Melosh have estimated that the
parent nucleus of the comet (before breakup) was only about 2 km across [13].
This would imply that the individual fragments are no larger than about 500
meters across.  Images of the comet taken with the Hubble Space Telescope in
July 1993 indicate that the fragments are 3-4 km in diameter (3-4 km is an
upper limit based on their brightness; the fragments have visual magnitudes of
around 23).  A more elaborate tidal disruption model by Sekanina, Chodas and 
Yeomans [20] predicts that the original comet nucleus was at least 10 km in 
diameter.  This means the largest fragments could be 3-4 km across, a size 
consistent with estimates derived from the Hubble Space Telescope's July 1993 
observations.  
     The new images, taken with the Hubble telescope's new Wide Field and
Planetary Camera-II instrument in 1994, have given us an even clearer view 
of this fascinating object, which should allow a refinement of the size 
estimates.  Some astronomers now suggest that the fragments are about 1 km or 
smaller.  In addition, the new images show strong evidence for continuing 
fragmentation of some of the remaining nuclei, which will be monitored by 
the Hubble telescope over the next two weeks.   One can get an idea of the 
relative sizes of the fragments by considering the relative brightnesses:
                   
--------------------       --------------------       --------------------
          Brightness                 Brightness                 Brightness
 Nucleus    Index           Nucleus    Index           Nucleus    Index
--------------------       --------------------       --------------------
  A=21        1              J=13        0             Q1=7a        3
  B=20        1              K=12        3               R=6        2
  C=19        1              L=11        3               S=5        3
  D=18        1              M=10        0               T=4        1
  E=17        2               N=9        1               U=3        1
  F=16        2             P2=8b        2               V=2        2
  G=15        3             P1=8a        0               W=1        2
  H=14        3             Q2=7b        2
--------------------       --------------------       -------------------

   The "brightness index" subjectively rates comet fragment brightnesses, 3 
being brightest. Brightnesses are eyeballed from the press-released HST image 
where possible.


Q2.7: How long is the fragment train?

     The angular length of the train was about 51 arcseconds in March 1993 
[2].  The length of the train then was about one half the Earth-Moon 
distance.  In the day just prior to impact, the fragment train will stretch
across 20 arcminutes of the sky, more that half the Moon's angular diameter.
This translates to a physical length of about 5 million kilometers.  The 
train expands in length due to differential orbital motion between the first
and last fragments.  Below is a table with data on train length based on 
Sekanina, Chodas, and Yeomans's tidal disruption model:

           +=============================================+
           |    Date    Angular Length  Physical Length  |
           |               (arcsec)          (km)        |
           +=============================================+
           |  93 Mar 25       49            158,000      |
           |     Jul  1       67            265,000      |
           |  94 Jan  1      131            584,000      |
           |     Feb  1      161            669,000      |
           |     Mar  1      200            762,000      |
           |     Apr  1      255            893,000      |
           |     May  1      319          1,070,000      |
           |     Jun  1      400          1,366,000      |
           |     Jul  1      563          2,059,000      |
           |     Jul 15      944          3,593,000      |
           |    Impact A    1286          4,907,000      |
           +=============================================+


Q2.8: Will Hubble, Galileo, etc. be able to observe the collisions?

     The Hubble Space Telescope, like earthlings, will not be able to see the
collisions but will be able to monitor atmospheric changes on Jupiter.  The 
impact points are favorable for viewing from spacecraft: it can now be stated 
with certainty that the impacts will all be visible to Galileo, and now at 
least some impacts will be visible to Ulysses.  Although Ulysses does not have
a camera, it will monitor the impacts at radio wavelengths.
     Galileo will get a direct view of the impacts rather than the grazing
limb view previously expected.  The Ida image data playback was scheduled to
end at the end of June, so there should be no tape recorder conflicts with
observing the comet fragments colliding with Jupiter.  The problem is how to
get the most data played back when Galileo will only be transmitting at 10 
bps.  One solution is to have both Ulysses and Galileo record the event and
and store the data on their respective tape recorders.  Ulysses observations
of radio emissions data will be played back first and will at least give 
the time of each comet fragment impact.  Using this information, data can 
be selectively played back from Galileo's tape recorder.  From Galileo's 
perspective, Jupiter will be 60 pixels wide and the impacts will only show 
up at about 1 pixel, but valuable science data can still collected in the 
visible and IR spectrum along with radio wave emissions from the impacts.  
     The impact points are also viewable by both Voyager spacecraft, 
especially Voyager 2.  Jupiter will appear as 2.5 pixels from Voyager 2's 
viewpoint and 2.0 pixels for Voyager 1.  However, it is doubtful that the 
Voyagers will image the impacts because the onboard software that controls 
the cameras has been deleted, and there is insufficient time to restore and
test the camera software.  The only Voyager instruments likely to observe 
the impacts are the ultraviolet spectrometer and planetary radio astronomy 
instrument.  Voyager 1 will be 52 AU from Jupiter and will have a near-limb
observation viewpoint.  Voyager 2 will be in a better position to view the 
collision from a perspective of looking down on the impacts, and it is also 
closer at 41 AU.


Q2.9: To whom can I report my observations?

     Observation forms by Steve Lucas are available via ftp at 
oak.oakland.edu in the /pub/msdos/astrnomy directory.  These forms also 
contain addresses of "Jupiter Watch Program" section leaders.  jupcom02.zip
contains Microsoft Write files.  The Association of Lunar and Planetary 
Observers (ALPO) will also distribute a handbook to interested observers.  
The handbook "The Great Crash of 1994" is available for $10 by ALPO Jupiter 
Recorder, Phillip W. Budine, R.D. 3, Box 145C, Walton, NY 13856 U.S.A.  The 
cost includes printing, postage and handling.
     John Rogers, the Jupiter Section Director for the British Astronomical
Association, will be collecting data from regular amateur Jupiter observers
in Britain and worldwide.  He can be reached via email ([email protected])
or fax (UK [223] 333840).  The Society of Amateur and Radio Astronomers (SARA)
is collecting radio observations of the events.  Observations can be sent to 
the chairman of the SARA Comet Watch Committee: Tom Crowley, 3912 Whittington
Drive, Altanta, GA 30342, EMAIL : [email protected].


Q2.10: Where can I find more information?

   The SL9 educator's book put out by JPL is in the /pub/astro/SL9/EDUCATOR
directory of SEDS.LPL.Arizona.edu.  There are two technical papers [18,19] 
on the atmospheric consequences of the explosions available at 
oddjob.uchicago.edu in the /pub/jupiter directory.  There are some PostScript 
images and text files involving the results of fireball simulations by 
Sandia National Laboratories at tamsun.tamu.edu (128.194.15.32) in the 
/pub/comet/sandia directory.
    SEDS (Students for the Exploration and Development of Space) has set up
an anonymous account which allows you to use "lynx" - a VT100 WWW browser.
To access this service, telnet to SEDS.LPL.Arizona.EDU and login as "www"
(no password required).  This will place you at the SEDS home page, from 
which you can select Shoemaker-Levy 9.  A similar "gopher" interface is 
available at the same site.  Just login as "gopher".
     Below is a list of FTP and WWW sites with SL9 information:

===============================================================================
     SITE NAME         IP ADDRESS       DIRECTORY                 CONTENTS
===============================================================================
SEDS.LPL.Arizona.EDU (128.196.64.66)  /pub/astro/SL9           Images & Info
oddjob.uchicago.edu                   /pub/jupiter                 Articles
jplinfo.jpl.nasa.gov (137.78.104.2)   /news and /images            Images
ftp.cicb.fr          (129.20.128.34)  /pub/Images/ASTRO/hst        Images
tamsun.tamu.edu      (128.194.15.32)  /pub/comet               Images & Info

===============================================================================
                            WORLD WIDE WEB SITES             
===============================================================================
         http://seds.lpl.arizona.edu/sl9/sl9.html                          
         http://info.cv.nrao.edu/staff/pmurphy/jove-comet-wham-2.html      
         http://pscinfo.psc.edu/research/user_research/user_research.html 
         http://cea-ftp.cea.berkeley.edu/Jupiter/
         http://http.hq.eso.org/educnpubrelns/comet.html
         http://www.gsfc.nasa.gov/planetary/COMET.HTML
         http://newproducts.jpl.nasa.gov/sl9/sl9.html


     If you have only mail access then try mailing the following message
(no subject) to [email protected]:
                                                     
ftp SEDS.LPL.Arizona.EDU
user anonymous [email protected]
cd /pub/astro/SL9/info
get factsheet.txt
dir

     Use your email address in the place of "[email protected]".  The file 
"factsheet.txt" should then be mailed to your account.  Other files 
can be retrieved in a similar manner from most ftp sites.  For more 
information about this service mail just the word "HELP" or "HOWTOFTP" to 
[email protected].

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

REFERENCES

[1]  "Update on the Great Comet Crash", Astronomy, December 1993, page 18.
[2]  Levy, David H., "Pearls on a String", Sky & Telescope, July 1993,
      page 38-39.
[3]  Melosh, H. H. and P. Schenk, "Split comets and the origin of crater
      chains on Ganymede and Callisto"  Nature 365, 731-733 (1993).
[4]  "Jupiter on Your Shortwave", Sky & Telescope, December 1989, page 628.
[5]  "Comet on a String", Sky & Telescope, June 1993, page 8-9.
[6]  "Comet Shoemaker-Levy (1993e)", Astronomy, July 1993, page 18.
[7]  "A Chain of Nuclei", Astronomy, August 1993, page 18.
[8]  "When Worlds Collide : Comet will Hit Jupiter", Astronomy,
      September 1993, page 18.
[9]  Burnham, Robert "Jove's Hammer", Astronomy, October 1993, page 38-39.
[10] IAU Circulars : 5800, 5801, 5807, 5892, and 5893
[11] Observers Handbook 1994 of the R.A.S.C., Brian Marsden.
[12] Sekanina, Zdenek, "Disintegration Phenomena Expected During Collision
      of Comet Shoemaker-Levy 9 with Jupiter"  Science 262, 382-387 (1993).
[13] Scotti, J. V. and H. J. Melosh, "Estimate of the size of comet
      Shoemaker-Levy 9 from a tidal breakup model"  Nature 365, 733-735 (1993).
[14] Beatty, Kelly and Levy, David H., "Awaiting the Crash" Sky & Telescope,
      January 1994, page 40-44.
[15] Jewitt et al., Bull. Am. Astron. Soc. 25, 1042, (1993).
[16] "AstroNews", Astronomy, January 1994, page 19.
[17] "AstroNews", Astronomy, February 1994, page 16.
[18] Zahnle, Kevin and Mac Low, Mordecai-Mark, "The Collisions of Jupiter and
      Comet Shoemaker Levy 9", Icarus, Vol 108, page 1.
[19] Mac Low, Mordecai-Mark and Zahnle, Kevin "Explosion of Comet
      Shoemaker-Levy 9 on Entry into the Jovian Atmosphere",
      submitted to Astrophysical Journal (Letters) on 7 June 1994.
[20] Sekanina, Z., Chodas, P.W., and Yeomans, D.K, "Tidal Disruption and the
     Appearance of Periodic Comet Shoemaker-Levy 9", Astronomy &
     Astrophysics, in press.
[21] "On a collision Course with Jupiter", Mercury, Nov-Dec 1993, page 15-16.
[22] "Timing the Crash", Sky & Telescope, February 1994, page 11.
[23] "Capturing Jupiter on Video" Sky & Telescope, September 1993, page 102.
[24] North, Gerald, "Advanced Amateur Astronomy", page 296-298, (1991).
[25] "Backyard Radio Astronomy", Astronomy, March 1983, page 75-77.
[26] Harrington, J., R. P. LeBeau, K. A. Backes, and T. E. Dowling,
     "Dynamic response of Jupiter's atmosphere to the impact of comet
     Shoemaker-Levy 9" Nature 368: 525-527 (1994).
[27] David Morrison, "Satellites of Jupiter", page 392, (1982).
[28] Weaver, H. A., et al, "Hubble Space Telescope Observations of Comet 
     P/Shoemaker-Levy 9 (1993e).", Science 263, page 787-791, (1994).
[29] Duffy, T.S., W.L. Vos, C.S. Zha, H.K. Mao, and R.J. Hemley.  "Sound
     Velocities in Dense Hydrogen and the Interior of Jupiter"  Science 263,
     page 1590-1593, (1994).
[30] Harrington, J., R. P. LeBeau, K. A. Backes, & T. E. Dowling, "Dynamic
     response of Jupiter's atmosphere to the impact of comet P/Shoemaker-
     Levy 9", Nature 368, page 525-527, April 7, 1994.
[31] Olivares, Jose, "Jupiter's Magnificent Show", Astronomy, April 1994,
     page 74-79.
[32] Schmude, Richard W., "Observations of Jupiter During the 1989-90
     Apparition", The Strolling Astronomer: J.A.L.P.O., Vol. 35, No. 3.,
     September 1991.
[33] "Comet heads for collision with Jupiter",Aerospace America,April 1994,
      page 24-29.
[34] "Comet Shoemaker-Levy 9 and Galilean Eclipses", CCD Astronomy, Spring
     1994, page 18-19.
[35] Reston, James Jr., "Collision Course", TIME, May 23, 1994, page 54-61.
[36] Benka, Stephen G., "Boom or Bust", Physics Today, June 1994, page 19-21.
[37] Beatty, Kelly and Levy, David H., "Awaiting the Crash - Part II", Sky
     & Telescope, July 1994, page 18-23.
[38] Alan M. MacRobert, "Observing Jupiter at Impact Time", Sky & Telescope,
     July 1994, page 31-35.
[39] Van Horn, Larry, "Countdown to the Crash", Monitoring Times, June 1994,
     page 10-13.
[40] Mallama, Anthony, "Comet Shoemaker-Levy 9 and Galilean Satellite
     Eclipses", CCD Astronomy, Spring 1994, pages 18-19.
[41] B. M. Middlehurst and G. P. Kuiper, "The Moon, Meteorites
     and Comets",  Univ. Chicago Press, 1963.
[42] Boslough, Mark B., et al, "Mass and Penetration Depth of Shoemaker-Levy 9
     fragments from time-resolved photometry", Geophysical Research Letters 
     (in press), June 1994.
[43] Crawford, David A., et al, "The impact of Comet Shoemaker-Levy 9 on
     Jupiter", Shock Waves (in press) April 1994.
[44] Bruning, David, "The Comet Crash", Astronomy (June 1994) pages 41-45.
[45] Levy, David, "Collision course! : A comet is bearing down on Jupiter"
     Smithsonian, Vol 25 No 3 (June 1994) pages 62-71.
[46] Stephens, Sally, "Smash it up!", Mercury, March-Arpil 1994, pages 7-11
[47] Boslough, M.B., D.A. Crawford, A.C. Robinson, T.G. Trucano, "Watching for
     fireballs on Jupiter", submitted to EOS, 1994.


ACKNOWLEDGMENTS

     Thanks to Ross Smith for starting a FAQ and to all those who have
contributed :  Robb Linenschmidt, Mordecai-Mark Mac Low, Phil Stooke,
Rik Hill, Elizabeth Roettger, Ben Zellner, Kevin Zahnle, Ron Baalke,
David H. Levy, Eugene and Carolyn Shoemaker, Jim Scotti, Richard A.
Schumacher, Louis A. D'Amario, John McDonald, Michael Moroney, Byron
Han, Wayne Hayes, David Tholen, Patrick P. Murphy, Greg F Walz Chojnacki,
Jeffrey A. Foust, Paul Martz, Kathy Rages, Paul Chodas, Zdenek Sekanina,
Don Yeomans, Richard Schmude, Lenny Abbey, Chris Lewicki, the Students
for the Exploration and Development of Space (SEDS), David A. Seal,
Leonard Garcia, Raymond Doyle Benge, Mark Boslough, Dave Mehringer,
John Spencer, Erik Max Francis, John Rogers, Al Jackson, Lucy-Ann A. 
McFadden, Michael F. A'Hearn, Martin Otterson, Tom Crowley, and many 
others who have discussed this event on newsgroups.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

                                                          .  '
||||||||||||||||||||                                            .
|| Dan Bruton     ||                  .         .             .
|| Texas A & M    ||                `.           .
|| [email protected] ||               `.              ` : :        `
||||||||||||||||||||                                              .
                                                                     .


% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Tue, 12 Jul 1994 14:02:58 +0700
% Message-Id: <Pine.3.89.9407121314.A22344-0100000@bozo>
% Errors-To: [email protected]
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: "Dan Bruton, Texas A&M" <[email protected]>
% Subject: Comet/Jupiter Collision FAQ
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

  TV/Space reporting hit an all time low with the reporting on the Comet
Shoemaker-Levy impact at Jupiter. And this time the scientific community can
share the blame. 

  At several points during the weekend I flipped around searching for some sort
of report on what was going on. I saw very little competent reporting. About
all I saw was a room full of goofball idiots wooping it up and getting drunk. 

  And what for? If they had built something and landed it somewhere fine, but
all they did was look at a bunch of TV pictures along with the rest of us. At
the very least they could have used the TV time to explain what was going on.
If they wanted to get blitzed on champagne they could always go over to
someone's house after work. 

  Astronomers are a worse bunch of prima Madonnas than the entire 1990 Oakland
A's outfield combined. We give them the best telescopes money can buy, pay for
their time through grants. Then they insist on hogging the best results for
months at a time and when some major natural phenomena does happen they
congratulate themselves as if they had done it themselves and get wasted on
cheap wine. 

  Someone has to talk to the people we pay to run our telescopes, they are at
best an embarrassment.

  George 

George,
  One wonders whether or not you watch or enjoy sports?  Let's say the
Celtics have just won the NBA finals (as they have been known to in the
past).  Do you think that showing the winners celebrating in their locker
rooms is inappropriate?  If they want to do that type of thing, let them 
do it in the privacy of their own homes and not shock the kiddies.

To me, the events surrounding SL9 as it slams into Jupiter are very similar
to winning a sports event.  Sure, it's a natural event, would have happened
if no one had known and never bothered looking.  BUT, astronomers DID
find the comet.  Other astronomers than successfully calculated that it 
would collide with Jupiter.  Many astronmers times and telescopes are being
tied up for 6 days to view something, that prior to Saturday, was based 
entirely on speculation on whether or not they would see anything at all.
Now the data starts to trickle in, or rather flood in.  The first impact,
which is not the largest piece, shows up quite nicely and ensures that 
the rest of the planned observations will not be a wash. It seems quite 
natural to me that the people who discovered the comet and others who spent 
a great deal of time planning the observations and eventual analysis of the
data would be elated that they would indeed have data to analyze.  If you're
going to criticize them for a little celebration over this, well, I wonder
what you would have them do before you praise them.

And, if you are going to just go by the TV news coverage of the events, 
what the hell do you expect?  The major networks are pretty clueless as
far as reporting science goes, but they can easily understand a news briefing
where people are clebrating.  CNN probably has the best coverage outside of 
areas where you can get the NASA channels, and I did find some useful info
from taping and scanning through a 3 hour segment yesterday.  But even that
wasn't all that much.  If you want a more in-depth look at things, I 
recommend the PBS special this Wednesday, "The Great Comet Crash".  

And what's your problem about researches having exclusive access to their
own data for a few months?  What were you planning on doing with it?
This is their careers here, and this is a significant and 'once in a lifetime'
opportunity to gain some insight into Jupiter, comet's, and major collisions.
Let them have their chance to analyze things and then inform us of what
they think is going on.  Prima donna's?  Pretty poorly paid ones if you
really want to compare them to the Oakland A's.  

PeterT

<<< Note 853.73 by QUARRY::petert "rigidly defined areas of doubt and uncertainty" >>>

>  One wonders whether or not you watch or enjoy sports?  Let's say the
>Celtics have just won the NBA finals (as they have been known to in the
>past).  Do you think that showing the winners celebrating in their locker
>rooms is inappropriate?  

  Well these days the chances of the Celtics winning the NBA finals would be
about as remote as a comet slamming into a planet but regardless the analogy is
off base. 

  Say that the Celts were hardly ever on TV and there was very limited info as
to what they were up to. Then say that a group of sports announcers stumbled
onto a building in which the Celtics were playing and renamed the team after
themselves. 

  Then say that the game ended and rather than telling us what happened they
just celebrated even though they had little to do with what went on. And say
that since the networks didn't understand basketball they figured "Hey great,
now we don't have to talk about this basketball stuff we can show these ninnies
jumping around celebrating".

  Yes, that would be inappropriate. It would be a terrible job of sports
announcing just as what these people did was a terrible job of astronomy.

>And what's your problem about researches having exclusive access to their
>own data for a few months?  

  About 2 years ago I had a new bathroom put into my house. I called a plumber,
paid for the parts and labor and he came and did the work. He did not ask for
exclusive rights to use my bathroom for any amount of time after the work was
done.

  About 4 years ago we as a nation had a telescope put up into space. We
called astronomers, paid the parts and labor and they put the dam thing up into
space. But now for some reason they want exclusive rights to use our telescope
after their work was done. It makes no sense. If they paid for it fine but
we paid for it so why not show us the pictures as they come in?

  Ok, so I'm in a bad mood. I just hope I don't have to wait until 1996 to hear
some reasonable analysis and see the pictures of what ever it was that happened
on Jupiter while the bunch of loonies that are running our telescope drink
champagne at our expense. 

  George

     George, please take what I say contructively, but I think you
    are way way off base in your criticism of these atronomers,
    and very well respected people like Gene Shoemaker, his wife
    and Heidi Hammel, the lead scientist for the team of observers
    running the Hubble telescope to capture these views of the
     impacts. I also don't think you are grasping the significance
     of this astronomical event. This *is* the *FIRST* time that
     astronomers have *ever* been so privileged to witness such an
     event. These people (and many others in the background), have
    worked very hard over the last 16 months since the comet was
    first discovered, putting together predictive scenarios as to
    what might occur. Some of these predictions appear to have been
    very well modeled. Lets give them some credit for their hard
    earned efforts in setting up the programming of the Hubble telescope,
    and for their efforts in modeling. BTW, havn't you ever really
    celebrated for something you accomplished intellectually?
    That's all they are doing, and I for one think they deserve the
    notoriety they are now getting.
    This is an event which is the absolute culmination of some of
    these peoples careers. 
    I'll allow them a little celebrating.
    
    Bob

    re .last few
    
    Pictures are already available. (I saw a pointer to a 16 frame MPEG
    movie of one impact. If the network wasn't so damn slow from here I would
    get it myself.) That data for detailed analysis is withheld to allow PI
    etc. time to get credit for any results that flow from the data is
    established procedure. You may not like it but it certainly is not
    unique to this event.
    
    re .73
    
    which asked what they would have to do to get praise...the answer is
    obvious from George's original note viz. land something somewhere.
    
    However we really are talking about groups with different interests. To
    the celebrating scientists, successfully capturing data about a once in
    a life time (once in a ?) event is a major success. Any hardware
    involved is a means to an end.
    
    
    While it's "sink the boot into the coverage time"...I was a little
    surprised to hear an apparently reputable scientist comparing the
    images of one of the impacts with a scene from 2010 (when large numbers
    of monoliths stellify Jupiter). He was quick to point out that Jupiter
    was not going to stellify as a result of the impact of SL9 but there's
    enough confusion and ignorance out there without this sort of thing
    IMHO. Well, maybe he was just a bit excited...

RE celebrating

  I have no objection to people celebrating. If the Braves won the world series
I'd expect the Braves announcers to woop it up, but not before they told us what
happened and not before they were sure that the media had told the story. After
a big game I often switch the tube off once the celebration starts and I don't
mind because I've seen the game and the analysis. I'd mind a lot if the party
was all I saw.

RE        <<< Note 853.76 by AUSSIE::GARSON "achtentachtig kacheltjes" >>>

>That data for detailed analysis is withheld to allow PI
>    etc. time to get credit for any results that flow from the data is
>    established procedure. You may not like it but it certainly is not
>    unique to this event.

  Dam straight I don't like it. Why should someone be famous only because they
got to see the data earlier? As tax payers who pays for both the telescopes
and most of these people's salaries, how are we better off with data being held
back so that slower astronomers get a jump on faster ones? 
 
>    which asked what they would have to do to get praise...the answer is
>    obvious from George's original note viz. land something somewhere.

  No, in this case they would have gotten my praise for showing us data with
intelligent analysis as soon as it was available and by avoiding giving the
networks an excuse to fill the "comet" time showing us a party.
    
RE There are pictures now.

  Yes, the proper analysis is finally coming out, although I have yet to see
many pictures that are identified as being from Hubble. How many of the
pictures that we've seen were taken by Hubble?

  George

Oh come on, George... There's gif's on the net from Hubble. I've also seen an
mpeg series from Hubble. The pictures were impressive enough that nobody had to
say "this here's the impact site", simply a cheer went up as it came up on the
screen. Not everything needs the obvious stated before celebrating it. They
captured the image due to 16 months of calculations and were thrilled to see
that they DIDN'T have to say something like "this pixel is a little darker due
to the impact". This truely was an event and Man had nothing to do with it other
than to know when to watch. The size of the impacts is totally beyond our
capabilities. I venture a guess that if Galileo missed a midcourse correction
and slammed into Jupiter, we wouldn't see a thing. I also want to keep Shoemaker
and Levy working on finding more comets because I don't like the thought of
being on the recieving end of one of these events. Let them blow off work for
half an hour and enjoy a bottle of bubbly. They worked hard for it. Don't think
that that was business as usual just because of a CNN 10 second newsbite. It was
CNN that chose to focus on the celebration. If the story had been a file shot of
an observatory and a comment that the impacts were taking place, would you have
been happier? We were there for the initial image display.... sharing the moment.

    The footage with the celebration was from an unscheduled press
    conference (and some video from the STOC) held immediately after the
    first image had been received. They weren't sure they would see
    anything, so being able to see the impact site with minimal processing
    was cause for elation. They chose to share that news a couple of hours
    in advance of the scheduled briefing. I'm glad they did.
    
    And that is all there was to share at that time. Once the images had
    been through some processing, in time for the 10pm feed, they had a lot
    more to say.
    
    NASA has been beaming down 90-120 minutes of results each day,
    including a lot of Hubble material. The press is doing it's usual
    incompetent job of reporting, concetrating on the fluff. I don't think
    that is the fault of the astronomers.
    
    gary

RE           <<< Note 853.79 by STAR::HUGHES "Samurai Couch Potato" >>>
>                                -< lighten up >-

  Ok,

  Congradulations are in order to astronomers Shoemaker and Levy for smacking
Jupiter head on with a comet. What a shot. If only Italy's soccer team had
someone with as sharp an eye. Like the three tenors astronomers obviously
planned this event to coincide with the World Cup soccer match. 

  Best of luck 4 years from now when Shoemaker and Levy will no doubt take aim
another planet to celebrate the World Cup in France. Perhaps they will thrill
us all by wacking Saturn with an asteroid. 

  It appears that all 20 some odd clumps will hit their target. Let the party
begin. 

  George

    re .77
    
    I wouldn't claim to have an inside track on understanding all the
    rationale of the PI system but I offer the following explanation.
    
    Telescope time is permanently at a premium, with demand exceeding
    supply. Consequently it is rationed. Most likely therefore if an
    astronomer puts a request in to use the telescope to gather data
    on some object or event, s/he is giving up the chance to observe
    something else i.e. there is a cost to the astronomer. Thus so
    that the PI gets full value from the observations, detailed data is
    withheld for some time (six months or so?). It would hardly be fair
    if another astronomer could use the data from someone else's "time
    slice" and still get his/her own time slice. Note that for events
    where there is significant public interest, some images are released
    without the usual delay. In particular I notice that ESO was able to
    get images on their WWW portal within a few hours.
    
    If you want pictures I suggest you take a look at the jpl newproducts
    WWW page. You will find at least one from Hubble and Keck and quite a
    few from MSSSO. (Yeah, we've had a box seat down here. If I could take
    the time off I would have been interested to go up there myself.)
    
    re .80
    
    Actually I thought the comet was timed as a 21-gun salute to the 25th
    anniversary of the Apollo 11 mission, rather than the World Cup. (-:

    In regards to the previous 6 and .75, the amount of information being
    distributed appears to be more generous than other investigative
    targets (particularly from STI).  Obviously, public interest has
    influenced this somewhat.  As far as public "perception" of the
    scientific community's reaction to the initial findings, I believe
    that your general soundbite as a news source TV viewer probably had
    no reaction other than acknowledgement that something special was going
    on.  I will say that in more scrutiny, some "spokespeople" were more
    articulate than others.  The Shoemakers, initally were quite
    informative as to the cause and pssible effects of this event.  Their
    analysis later became more focused on the probabilities and
    reprocussions of an earth strike as opposed to the changes happening @
    Jupiter.  Heidi Hammel, IMHO was/is an embarassment.  Her wide-eyed
    "scientific" observations about "bam, bam, bam, it will make quite a
    mess" were not only poor statements of the obvious, but devoid of 
    any insightfullness.  I use that quote as an example, there were many
    many more both in news conferences and in private interviews.  My 8
    year old daughter had a dozen or more questions about the mechanics and
    physical processes going on that none of the spokespeople adequately
    addressed.  Let's hope that there will be something soon in one of the
    science mags.
      My $.02   

>  Heidi Hammel, IMHO was/is an embarassment.  Her wide-eyed
>    "scientific" observations about "bam, bam, bam, it will make quite a
>    mess" were not only poor statements of the obvious, but devoid of 
>    any insightfullness.

Ahh yes, but be sure to point out to your 8 year old daughter that here
is an example of a woman who is making a career in a field that is 
dominated by males.  Some of Heidi's comments may seem simplistic,
but you have to remember the audience is the general public who are not
very scientific literate.  If you watched the Great Comet Crash last night
on PBS, she did a reasonable job there, but did very well in a panel session
right afterwards, where she got into some more technical explanations of 
what they were seeing and what they had hoped to see.  Remember that she is
the head of one of Hubble teams studying this event, and it's likely she
did not get there just due to "wide-eyed enthusiam" (though that probably
didn't hurt ;-)  

PeterT

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 11-JUL-1994 
CC:	
Subj:	Comets, Asteroids & Meteor Educator Conference

COMETS, ASTEROIDS & METEORS EDUCATOR CONFERENCE
 
The July collisions of fragments of the comet Shoemaker-Levy 9 with
the planet  Jupiter are a once-in-a-lifetime event and an
extraordinary scientific opportunity.  Much media coverage has been
focused on this but the results of these impacts and interpreting them
for the classroom cannot be done in the popular press. 
 
The same is true of the first close-up pictures ever taken of
asteroids. The Galileo spacecraft, enroute to Jupiter, has flown close
by the asteroids Gaspra and Ida and returned high resolution images. 
New ground-based radar techniques have been used to image asteroids
that have flown close to Earth. 
 
Earth is impacted daily by small bits of cometary and asteroidal
debris, periodically by vast swarms of material and, on rare
occasions, by objects that result in cataclysmic changes in the
evolution of life on Earth.  All of these types of objects form a
tapestry that adds to the richness and complexity of our solar system.
 
In view of these events, the NASA  Education Division, the Jet
Propulsion Laboratory (JPL) Public Education Office and the JPL Public
Services Office cordially invite you to attend the COMETS, ASTEROIDS &
METEORS EDUCATOR CONFERENCE.  The conference is scheduled from 12:00
p.m. on Friday, August 12 to 12:00 noon on Sunday, August 14, 1994 and
will include the following events: 
 
EDUCATORS CONFERENCE 

Scientists will describe the Shoemaker-Levy 9 collisions and the early
results of its effect on Jupiter.  Project scientists and engineers
will discuss the Galileo spacecraft's observations of the events and
the data from the asteroid flybys.  Astronomers will describe meteor
showers and the contributions of all of these small objects to our
understanding of the formation and evolution of the solar system and
the planet Earth. 
 
EDUCATORS RECEPTION

A special reception featuring a briefing on the Galileo mission to
Jupiter will be held for all educators. 
 
TEACHER WORKSHOP

This workshop will provide information on applying comet, asteroid and
meteor science in the classroom. 
 
Special Notes:

   o  Participation in the COMETS, ASTEROIDS & METEORS EDUCATOR CONFERENCE 
      is limited to 400 persons.  The conference will be opened to
      the general public only if space permits on August 3. 
 
   o The conference will take place at Ramo Auditorium on the Caltech campus.
 
   o Registration fee: $65
 
For additional information and a registration packet, contact the
Public Services Office, Mail Stop 186-113, the Public Education
Office, Mail Stop CS-530, or e-mail David M. Seidel at:
[email protected] 

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Mon, 11 Jul 1994 19:49:38 +0700
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: Ron Baalke <[email protected]>
% Subject: Comets, Asteroids & Meteor Educator Conference
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US4RMC::"[email protected]" "Ron Baalke" 26-JUL-1994 
To:	[email protected]
CC:	
Subj:	450 Comet Shoemaker-Levy Impact Images Available

The JPL Comet Shoemaker-Levy Home Page now has the world's largest
collection of comet impact images. Available are over 450 different
images from 31 different observatories.  The URL for the home page:

http://newproducts.jpl.nasa.gov/sl9/sl9.html

       OR

http://navigator.jpl.nasa.gov/sl9/sl9.html

      ___    _____     ___
     /_ /|  /____/ \  /_ /|     Ron Baalke     | [email protected]
     | | | |  __ \ /| | | |     JPL/Telos      | 
  ___| | | | |__) |/  | | |__   Galileo S-Band | You cannot achieve the 
 /___| | | |  ___/    | |/__ /| Pasadena, CA   | impossible without attempting
 |_____|/  |_|/       |_____|/                 | the absurd.


From:	US4RMC::"ASTRO%[email protected]" "Astronomy Discussion 
        List" 26-JUL-1994 09:31:43.96
To:	Multiple recipients of list ASTRO <ASTRO%[email protected]>
CC:	
Subj:	Preliminary list of sites with SL9 crash images (Revised 4th ed)

Preliminary list of sites holding images of the SL9-Jupiter crash (Revised)

- compiled by Hartmut Frommert <[email protected]>
  updates and additions welcome
- rearranged to order by IP address
  (i.e., domain/country first, and here US/International first)
  according to proposition of John Van Essen <[email protected]>
-----------------------------------------------------------------------------

FTPMAIL:

  [email protected]: /pub/astro/SL9/images/recent_images

  - According to [email protected] (Andrew Tubbiolo):

  > Mail a file like the following to [email protected].
  >   open
  >   cd /pub/astro/sl9/recent_images/ALL
  >   uuencode      <--This is a default setting, mmencode is also available.
  >   get [image].[name]
  >   close
  > For a list of whats there get 00Index.gif and 00Index1.gif from the above
  > path.

GOPHER:

  seds.lpl.arizona.edu: /pub/astro/SL9/images/recent_images

FTP:

  ftp.iglou.com: /comet/images
  ftp.interaccess.com: /Jupiter/">ftp
  ftp.netcom.com: /pub/billa/
  pluto.neosoft.com: /pub/space/sl9    (mirrors stsci.edu)
  dept.physics.upenn.edu: /SL9
  ftp.u.washington.edu: /public/roland/sl-images
  hollebeek.hep.upenn.edu: /SL9
  nscp.physics.upenn.edu: /SL9
  observ.fi.edu:/SL9
  seds.lpl.arizona.edu: /pub/astro/SL9/images/recent_images
                       /pub/astro/SL9/animations/saao.mpg (Animation A crash)
  stsci.edu: /stsci/epa/comet/gif,/stsci/epa/comet/jpeg (Hubble images)
  tamsun.tamu.edu (128.194.15.32): /pub/comet and /incoming
  nssdca.gsfc.nasa.gov
  ecf.hq.eso.org: /pub/sl9-eso-images  (ESO images)
  ftp.rdt.monash.edu.au: /pub/jupiter-sl9
  gco.apana.org.au: /pub/jupiter/sun-col.gif (amateur image)
  minnie.cs.adfa.oz.au: /SL9    (mirror of ftp.rdt.monash.edu.au)
  myasthenia.dci.uwa.edu.au: /pub/seds/astro/sl9/images/recent (mirrors seds)
  ftp.cs.tu-berlin.de: /pub/astro/images/SL-9/
  ftp.med-stat.gwdg.de: /pub/SL9-Impact/  (IMAGES!)
  ftp.mpia-hd.mpg.de: /pub/sl9
  ftp.cnam.fr: /pub/Astro/incoming
  ftp.univ-rennes1.fr (129.20.254.1): /pub/Images/ASTRO/cometSL9
  sir.univ-rennes1.fr: /pub/Images/ASTRO/hst
  ftp.ru.ac.za (146.231.128.1): /pub/saao  (South African Images)
  kudu.ru.ac.za (146.231.128.5): /pub/saao  (South African Images)

WWW

  ftp://ftp.iglou.com/comet/images
  ftp://ftp.netcom.com/pub/billa/billa.html
  http://pluto.neosoft.com/   (mirrors stsci.edu)
  http://dept.physics.upenn.edu/SL9
  http://alfred1.u.washington.edu:8080/pub/roland/sl/sl.html
  http://hollebeek.hep.upenn.edu/SL9
  http://nscp.physics.upenn.edu/SL9
  http://observ.fi.edu/SL9
  http://pdssbn.astro.umd.edu:80/c1993e/ftp/pub/images
  http://seds.lpl.arizona.edu/sl9/sl9.html
  http://www.het.brown.edu/news/index.html
  http://zebu.uoregon.edu/comet.html
  http://navigator.jpl.nasa.gov/sl9/sl9.html   (mirror of newproducts.jpl...)
  http://newproducts.jpl.nasa.gov/sl9/image1.html (Hubble image before crash)
  http://newproducts.jpl.nasa.gov/sl9/sl9.html (Over 450 images collection !)
  http://stardust.jpl.nasa.gov/planets/
  http://www.gsfc.nasa.gov/planetary/COMET.HTML   (NSSDC)
  http://http.hq.eso.org/eso-homepage.html  (ESO images)
  ftp://ftp.rdt.monash.edu.au
  ftp://myasthenia.dci.uwa.edu.au:/pub/seds/astro/sl9/images/recent
  http://meteor.anu.edu.au/home.html
  http://www.rdt.monash.edu.au
  http://www.cnam.fr/astro.english.html (Comet directory)
  ftp://ftp.riken.go.jp/pub/astro/SL9/images/recent
  ftp://ftp.ru.ac.za:/pub/saao/images/

------------------------------------------------------------------------------

  Hartmut Frommert             | Russia HAS a space station !
  <[email protected]> | Mars Observer 2 would have survived.

----------- Get astronomical and space gifs via anon ftp from: -------------
explorer.arc.nasa.gov: /pub/SPACE/GIF; ftp.univ-rennes1.fr; ftp.cnam.fr    |
seds.lpl.arizona.edu; images.jsc.nasa.gov; jplinfo.jpl.nasa.gov; | Updates |
Hubble: stsci.edu: /stsci/epa/gif  Clementine: clementine.s1.gov | welcome |
- More in SEDS' Astro FTP List:  ftp://seds.lpl.arizona.edu/faq/astroftp.txt

The SL9 crash was just a heavenly celebration of Apollo 11 25th anniversary!

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Tue, 26 Jul 1994 15:16:18 +0100
% Reply-To: Astronomy Discussion List <ASTRO%[email protected]>
% Sender: Astronomy Discussion List <ASTRO%[email protected]>
% From: Hartmut Frommert <[email protected]>
% Subject: Preliminary list of sites with SL9 crash images (Revised 4th ed)
% To: Multiple recipients of list ASTRO <ASTRO%[email protected]>

From:	US4RMC::"[email protected]" "MAIL-11 Daemon" 29-JUL-1994 
CC:	
Subj:	JPL Radio Observations of Comet Shoemaker-Levy

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109.  TELEPHONE (818) 354-5011

Contact:  James H. Wilson

FOR IMMEDIATE RELEASE                                July 29, 1994

     Radio astronomers at NASA's Jet Propulsion Laboratory were
surprised by an unexpectedly great increase in Jupiter's microwave
emissions apparently associated with the bombardment of the planet
by the fragmented Comet Shoemaker-Levy 9.

     Dr. Michael J. Klein reports that the increase in radio
intensity began soon after July 16 and peaked July 23 when the
intensity was 25 percent greater than it had been before the comet
encounter. It has been slowly fading each day since July 23, but
is still much higher than normal.

     "Although some researchers anticipated changes in Jupiter's
radio output during the comet impacts, this powerful increase was
unlike anything predicted before the events," Klein said.

     The increase was apparent on July 21 when data taken at 2295
Megahertz with a 34-meter-diameter (112-foot) R&D antenna at
Goldstone, California, were analyzed, he added. Astronomers in
Australia have reported a similar increase in radio emissions, but
at much longer wavelengths.

     The research is part of the NASA/JPL Jupiter Patrol, a
long-term radio astronomy monitoring program begun in 1971 and
intensified in January 1994 in response to predictions of the
cometary impacts in July.  "We've never seen anything like this in
the 23 years of the program," Klein said.  "It's a big surprise."

     Goldstone is one of three sites used by the NASA/JPL Deep
Space Network to communicate with distant spacecraft such as
Voyager and Galileo, but its giant dish antennas are frequently
used as sensitive radio telescopes.

     JPL radio astronomers are cooperating with a worldwide
community of observers coordinated by Dr. Imke dePater of the
University of California, Berkeley, which used such instruments as
the 64-meter (210-foot) Parkes Telescope in Australia, the 43-
meter (140-foot) National Radio Astronomy Observatory in
Greenbank, West Va., the NRAO 27-antenna Very Large Array in New
Mexico, the Naval Research Laboratory's instrument near
Washington, D.C., and telescopes in the Netherlands and Germany.

     Klein added that radio emissions from Jupiter originate from
the giant planet's atmosphere and from its ring-like belts of
charged particles, similar to Earth's Van Allen belts.

     Dr. Samuel Gulkis, Klein's colleague in the Jupiter patrol,
suggested that the impacting comet or the ensuing explosions may
have enhanced Jupiter's belt of energetic electrons, circling the
planet and trapped by its magnetic field.

     "The interesting question is how the interaction of the comet
with Jupiter accelerates the electrons to relativistic speed and
traps them, at least temporarily, in the planetary magnetic
field," Gulkis said.  "The answers may provide a better insight on
how the Sun produces its intense bursts of radio energy which
sometimes interfere with communications on Earth."

     The Jupiter Patrol is operated and managed by JPL for NASA's
Office of Space Science and Office of Space Communication.

                              #####

From:	US4RMC::"[email protected]" "MAIL-11 Daemon"  1-AUG-1994 
CC:	
Subj:	Galileo Playback Schedule for SL9 Images

Galileo playback and sequence schedule for Comet Shoemaker-Levy images.

>From Michael Belton, Galileo Solid State Imaging (SSI) Prinicpal Investigator.

JBS = Jail Bar Search

7/29-7/30........JBS of D downlinked 

7/31-8/2.........JBS of E downlinked 

8/1-8/2..........MIPL processes D & E JBS's 

8/2 EOD..........SSI delivers starting point of each 75-line swath of data
return for D & first swath of E to sequence integrator 

8/4-8/6..........JBS of K downlinked 

8/7-8/12.........JBS of N downlinked 

8/8..............RBS #2 uplinked (contains return slews for D & part of E) 

ASAP after 8/13..SSI delivers starting point of remaining 75-line swaths for
impact E, data return times for K & N, and JBS for V & W to sequence integrator 

8/13-8/14........DATA RETURN FOR D ****** FIRST DATA ******* this is a weekend,
data should be available Monday 8/15 

9/7..............RBS #3 uplinked (contains JBS slews for V & W) 

9/12-9/18........Data return for E 

9/18-9/21........JBS of V downlinked 

9/22-9/24........JBS of W downlinked-9/24 

9/26.............SSI delivers starting point of each 75-line swath of data
return for V & W to sequence integrator. 

10/7-10/15.......Data return for K 

10/17-?..........Data return for N 

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date: Mon, 1 Aug 1994 17:09:49 +0700
% Errors-To: [email protected]
% Reply-To: [email protected]
% Originator: [email protected]
% Sender: [email protected]
% From: Ron Baalke <[email protected]>
% Subject: Galileo Playback Schedule for SL9 Images
% X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US1RMC::"[email protected]" "Ron Baalke" 12-AUG-1994 
To:	[email protected]
CC:	
Subj:	Galileo Begins Sending Shoemaker-Levy Data

Sarah Keegan
Headquarters, Washington, D.C.      August 12, 1994
(Phone:  202/358-1547)

James H. Wilson
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone:  818/354-5011)

RELEASE:  94-133

GALILEO BEGINS SENDING SHOEMAKER-LEVY DATA

      NASA's Galileo spacecraft has begun a six-month process of
radioing to Earth data taken during the collisions of Comet
Shoemaker-Levy 9 at Jupiter in July.

      From its vantage point in space en route to Jupiter,
Galileo had the only direct view of the collisions of comet
fragments on the dark side of the giant planet, July
16-22. Galileo stored observational data on its onboard tape
recorder and is transmitting the data to Earth via its low-gain
antenna over several months.

      Ground controllers initially instructed Galileo to send
back "jail-bar" image strips -- narrow slices of various portions
of data -- to help them search for the most promising
observations on the spacecraft's tape recorder.  Preliminary
looks at "jail-bar" data recently sent to Earth of the impact of
the comet's fragment K led scientists to confirm detection of an
intense burst of light lasting about 40 seconds.

      These data are from a special time exposure frame that
forms a streak from Jupiter and another from the impact flare,
providing high resolution in time and brightness.  More data from
the K event will be sent to Earth in October.

      Other data still stored on board the spacecraft include
images of the fragment W impact.  Mission scientists do not yet
know whether the actual impact was captured on these frames.  A
small portion of the fragment W data will be sent to Earth in
mid-August and late September and the rest is scheduled to be
received in January.

      Data from the fragment G impact were taken with Galileo's
ultraviolet spectrometer, the infrared mapping spectrometer and
the photopolarimeter.  These data will be returned starting in
late September and continuing through December.

      Galileo data primarily of interest to scientists and
amateur astronomers will be posted on an ongoing basis on the
Internet via the World Wide Web system.  This may be accessed by
the public from the home page of NASA's Jet Propulsion
Laboratory (JPL), Pasadena, Calif., at the address
http://www.jpl.nasa.gov/ under
the "News" heading.

      If comet impact images of more general interest are
received, they will be released through the newsrooms at NASA
Headquarters, Washington, D.C., and at JPL.

 - end -

Article: 4129
From: [email protected] (Syed S. Towheed, Hughes STX, 
      NSSDC NASA-GSFC)
Newsgroups: alt.sci.planetary
Subject: Galileo SL-9 Impace Image
Date: 12 Aug 1994 16:41 EDT
Organization: NASA Goddard Space Flight Center -- Greenbelt, Maryland USA
 
        FIRST GALILEO SL-9 "JAILBAR" IMAGE AVAILABLE AT THE NSSDC
 
The National Space Science Data Center (NSSDC) at NASA's Goddard Space
Flight Center is pleased to announces the availability of the latest
Comet P/Shoemaker-Levy 9 impact images taken by the Galileo spacecraft. 
 
The images can be obtained using the World Wide Web (WWW) via the URL below.
 
              http://nssdc.gsfc.nasa.gov/sl9/comet_images.html
 
As of 4:00 pm EST, August 12, 1994, we only have the first "Jailbar"
image, but we will be providing the full resolution images as soon as
they become available. 
 
Syed S. Towheed
Systems Programmer
Hughes STX Corp.
 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
National Space Science Data Center                           Phone:(301)286-6695
NASA Goddard Space Flight Center                               Fax:(301)286-1635
Greenbelt, MD 20771, USA                     E-mail:[email protected]
 
http://www.gsfc.nasa.gov/nssdc/nssdc_home.html
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
 
Article: 4135
From: [email protected] (Chris Lewicki - LPL)
Newsgroups: sci.astro,sci.space.science,alt.sci.planetary
Subject: First Galileo SL9 Image Available!
Date: 12 Aug 1994 20:48:50 GMT
Organization: University of Arizona, CCIT
 
The first Solid State Imaging (SSI) data showing the impact of Comet
Shoemaker-Levy 9 fragment K onto Jupiter has been received from the
Galileo spacecraft.  The image and text description are available
through anonymous ftp at SEDS.LPL.Arizona.EDU in the directory: 

/pub/astro/SL9/recent_images/ALL (or just sl9recent) in the files
 
GAL_K1.GIF
GAL_K1.txt.  
 
Here are the first few paragraphs from the text file:
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
 
The partial image of the K impact represents the return of image
search "jailbars" - groups of 2 lines every 80 lines. The wide gaps
will be filled in at a later time tentatively scheduled for
mid-October, 1994. 
 
The data, obtained between 10:23:10 and 10:25:37 UT July 19, 1994
(Earth receive time), shows the entry of fragment K, which looks like
a bright flare on the dark side of Jupiter (directly visible from
Galileo's perspective) between the terminator and the dark limb of the
planet lasting approximately 35 seconds. The flare at its brightest is
about 10% the total brightness of Jupiter (at this phase angle = 50 deg.) 
 
--
------------------------------------------------------------------------------
Chris Lewicki  +  (602) 621-9790  +  (602) 621-9626  +  [email protected] 
Maintainer of SEDS.LPL.Arizona.EDU
             'Legendary' Mars Observer GRS Flight Investigation Team
UA SEDS President			 SEDS-USA Director of Special Projects
------------------------------------------------------------------------------

From:	US1RMC::"[email protected]" "HILL, DIANNE" 19-AUG-1994 20:57:57.21
To:	release <[email protected]>
CC:	
Subj:	N94-62 GALILEO COMET IMPACT PICTURE RELEASED

Sarah Keegan
Headquarters, Washington D.C                               August 19, 1994
(Phone:  202/358-1902)

Ed McNevin
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone:  818/354-5011)

NOTE TO EDITORS:  N94-62

GALILEO COMET IMPACT PICTURE RELEASED

     The first picture taken by NASA's Galileo spacecraft of an impact of a
fragment of Comet Shoemaker-Levy 9 has been released by the space agency.

     The black-and-white image of the collision of comet fragment W
consists of four frames taken over a 7-second period.  It shows the
beginning, brightening and fading of a bright point about 44 degrees
south latitude on the far side of Jupiter from the Earth.  The four
frames were obtained on July 22, 1994, at a distance of about 150
million miles from Jupiter. 

     News media representatives may obtain copies of the picture by
faxing a request to NASA Headquarters' Broadcast and Imaging Branch at
202/358-4333 and requesting photo numbers 94-HC-195 (color) or
94-H-218 (black and white), or by calling NASA's Jet Propulsion
Laboratory, Pasadena, Calif., at (818) 354-5011. 

      The image may also be accessed by the public electronically by
Internet via the World Wide Web system, from JPL's home page at the
address http://www.jpl.nasa.gov/ under the "News" heading; or by
anonymous file transfer protocol (FTP) to the address
jplinfo.jpl.nasa.gov in the "News" directory.  The file may also be
accessed via JPL's dialup bulletin board system at (818) 354-1333. 

                            -end-

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% From: "HILL, DIANNE" <[email protected]>
% To: release <[email protected]>
% Subject: N94-62 GALILEO COMET IMPACT PICTURE RELEASED
% Date: Fri, 19 Aug 94 14:56:00 PDT
% Sender: [email protected]

Article: 4191
Newsgroups: alt.sci.planetary
From: [email protected] (Susanne Huttemeister)
Subject: Invitation to contribute to the upcoming SL9 - Book
Sender: [email protected]
Organization: Smithsonian Astrophysical Observatory, Cambridge, MA, USA
Date: Thu, 25 Aug 1994 19:07:51 GMT
 
This should be of interest to many of you.
 
Please respond directly to the author, German science journalist 
Daniel Fischer, at the address given below. If you absolutely have
to, you can also reach him through me.
 
         Susanne
 
-----------------------------------------------------------------------
 
Dear observers of the SL9/Jupiter collision!
 
While the subsequent invitation has been directed primarily towards
professional astronomers who observed the comet/Jupiter collision, 
there must be also countless good observations (drawings and photographs
alike) out there in the amateur community, as well as at least as many
good stories to tell - in particular if you shared your telescope with
the general public. Let them come: We would like to present the
unbelievable SL9 event in *all* it's aspects!
 
The Swiss science book publisher Birkhaeuser will prepare a book on the
SL9 event as early as this November, directed at a general but
astronomically interested audience. After the IAU GA it is clear that 
the definitive work on 'what was  l e a r n e d' can come only much 
later, so the focus will be on the scientific process itself. In a style 
reminiscent of the NASA SP books 'Voyage to Jupiter' and 'Voyages to
Saturn' or also Nigel Calder's 'Giotto to the Comets',
the authors (Holger Heuseler and myself) will try to tell the
story of how the eventful week took place in many places of the world
simultaneously (I myself have been an eyewitness on Cerro Tololo), carry
the best data (images and otherwise) that were available in near real-time
and interweave the first results of a bit more detailled analysis that
was done in the past month. 
 
For the 'science as it happened' part we will rely on the SL9 mail exploder
reports and similar message systems, for the 'instant science' on the
daily NASA newsconferences and for the 'fast science' on the 9 hours of
sessions that took place in The Hague last week. However, what we would
like to include besides these sources are more personal contributions
from individual amateur and professional observers from around the world:
 
  - What were your expectations and main programs you had prepared
  for the impact week? Or did you expect 'nothing at all' and were
  making up observing plans as you went along? Did you collect a good
  set of recent Jupiter observations before the impact (a 'baseline)?
 
  - When did you have your first sighting of a dark spot? Did you see
  one that was really 'fresh' (i.e. during it's dirst rotation)?
  How did the spots evolve in the early days, how are things now?
 
  - Did you participate in public events? How many people came? There
  was a most remarkable report on sci.astro.planetarium from NYC with
  7000 one night - can you top that? How did people react? Were they
  duly impressed? Did they grasp the enormous size of these spots?
 
And what we would appreciate most would be images, images, images! CCD
pictures, drawings, sketches, everything is welcome, in particular if it
reveals also some details inside the spots. If you send a written report
or just some statements 'how it was like to you' they'll probably be
included in the main text, but longer contributions or statements, in
particular those addressing specific details of an observation or 
a noteworthy event surrounding SL9's demise, could very well become
individual sidebars or boxes (here also more technical illustrations
would be welcome). While the book in its present form will be published
in German, all quotes and contributions will be stored in their original
form, so a possible future international edition could draw directly on them.
 
If you would like to contribute to this project, please reply soon (but
DO NOT use the auto-reply function - this was posted by a friend!):
  
  send texts, graphis or images by e-mail to 
 
                     [email protected] 
  or fax them 
                    (+49-2244-80298)
  or mail 
           (Daniel Fischer, Im Kottsiefen 10, 53639 Koenigswinter, Germany).
 
I will be in the U.S. for the next two weeks (Cambridge + Amherst, MA, and
various SL9-related institutions in Maryland) but will remain on-line
during the first. As the text will take shape between Sept. 10 and 25,
timely replies would be most welcome.
 
Many thanks for your support - everything is appreciated! Spread the
news about the book project also in your local societies, if you like.
 
Daniel Fischer for the Birkhaeuser publishing house, Basel, Switzerland
  

From:	FLAMBE::"[email protected]" 31-AUG-1994 12:43:57.86
To:	Multiple recipients of list <[email protected]>
CC:	
Subj:	Update on comet collision vs. KT impact theories

As promised, here is the scoop on the Shoemaker-Levy 9 impact from the
International Astronomical Union general assembly in The Hague the
last couple of weeks. I sneaked away from galaxy sessions for one of
the Jupiter/SL9 sessions. Much of what follows is taken from talks by
Mike A'Hearn (University of Maryland), Heidi Hammel (MIT), John Clarke
(University of Michigan), and Keith Noll (Space Telescope Science
Institute). I have added a bit of material on the comet orbital
dynamics and which directions might be needed to scale these events in
understanding impacts on Earth (though this does go beyond my
specialty so I have exercised some restraint). 

The comet's orbit : A'Hearn pointed out that we were properly
discussing the former Jovian satellite Shoemaker-Levy 9. While
prediscovery observations after the tidal breakup have been found,
none has turned up before then. This raises the possibility that there
could be more such objects currently in Jovian (Jovicentric?) orbits
but too faint to see. The latest orbit passed in July 1992 within 1.5
Jupiter radii, carrying the comet inside the classical Roche limit for
tidal breakup for 1.5 hours (Gravity - not just a good idea. It's the
law), and out to apojove (our word for the month) 0.3 astronomical
units (45 million km) from the planet. At this distance, solar
perturbations are very important (which is what made the orbit
unstable). For such a highly inclined, retrograde orbit in that
direction, solar perturbations decreased the orbital angular momentum,
with the now well-known spectacular results. The comet was in Jupiter
orbit for several decades; available observations cannot be more
specific because the previous orbit determinations are very sensitive
to the perijove at each encounter, which in turn is very sensitive to
small errors in the current orbit (in fact, it has n discussed as
satisfying the criteria for chaos over this period). 

    This temporary capture works because Jupiter (a) has numerous
satellites, some massive, and more important (b) sits in the solar
gravitational well. The parameter space for Earth to capture such an
object is much smaller. In fact, Clyde Tombaugh made an extensive
search for small natural Earth satellites shortly before such a search
was rendered impossible by artificial satellites (obviously with null
results). However, Earth can certainly disrupt comets by tidal forces
- the moon has crater chains that look much like SL9 would have
produced. A good example is Davy Catena (formerly the Davy Y chain)
near the center of the lunar earthside. Good images can be found on
page 97 of NASA SP-200, The Moon as Viewed by Lunar Orbiter, and plate
297 (upper right corner) of NASA SP-206, Lunar Orbiter Photographic
Atlas of the Moon. 

    In this case, the impact speed was dominated by Jupiter's escape
velocity, since the object was gravitationally bound to Jupiter (but
just barely). This is not likely to be the case for Earth impacts, as
has been pointed out by others. Jupiter's escape velocity is larger
than circular-orbit velocity at its distance from the Sun, while the
opposite holds in our case. Comets are likely to have higher impact
speeds than asteroids, which are in more nearly circular and direct
(not retrograde) orbits. 

Was this a comet or an asteroid before breakup? Not a trivial
question. It certainly acted cometary after breakup - dust tails,
disappearing and brightening/fading fragments. On the other hand, we
don't know that asteroids don't act this way when broken up, having
never seen such a thing happen. When sideswiped, asteroids do produce
dust trails (seen in the far-infrared by their own thermal emission).
SL9 showed (as far as I know) no evidence that any gas was being
released from the fragments, and for that matter no dust except what
had been released at breakup. New observations from the Kuiper
Airborne Observatory showed water in some of the impact plumes, and
the time behavior has been taken to suggest that it came from the
fragments. If so, this sounds like a genuine comet. 

     SL9 was certainly cometary when it hit Jupiter. Some very
impressive (and difficult) observations of fragments only a few hours
before impact show the dust clouds stretching out along the radius
vector, strongest toward Jupiter, as expected from tidal acceleration
(and the string of pearls stretched some millions of km at this point
for the same reason). 

Mass of the impacting fragments: from the energy budget of the impact
fireballs, the largest ones had masses of order 10^14 g. For solid
ice, this gives a diameter of about  0.6 km, larger if it had a porous
or "snowball" structure. A nickel/iron meteor with the same punch
would have a diameter smaller by the cube root of the density ratio,
or about 1.6x. The energy released in the larger impacts was about
2x10^27 ergs (or for all you ex-cold warriors out there, I make it
close to 10^5 megatons of TNT). This scales as the square of the
impact velocity, so a similar impactor would (likely but not
guaranteed) give a smaller energy release on Earth. 

     One real puzzle is the lack of obvious meteor phenomena.
Comparison of times of flashes seen by Galileo with Earth-based IR
observations shows that no brilliant flash occurred on atmospheric
entry until the fragments dropped below the cloudtops - stealth
comets! The only possible exceptions were, curiously, the fragments
that left little or no trace of the cloudtops, and were (even more
curiously) offset from the main line of fragments (density effects???)
- some of these have unconfirmed reports of flashed reflected from the
large Jovian satellites. 

Where did they explode? The upper Jovian atmosphere has three major
cloud layers in a hydrogen-rich matrix. Lacking a sea level, it is
usual to reference height to the one-bar pressure level. On this
scale, the visible cloud tops are ammonia at about +50 km, NH_3SH at
about 0 km, and water clouds at about -20 km. No explosions seemed to
dredge up significant water, and indirect indications (such as the
center of shock waves compared to entry points seen in HST images)
agree that the fragments exploded perhaps a couple of hundred km below
the top clouds but (from spectroscopy) above the water clouds (a small
amount of H2O did eventually turn up in spectra of the impact sites).
In an Earth impact, the fragments would have hit the surface instead
of such an air burst, as the column density and pressure are less
through our entire atmosphere than the fragments traversed. 

     The explosions channeled much of the rising material back along
the low-density channel left by the incoming fragment (predicted by at
least one simulation at Sandia Labs - in Shock Waves 4, 47., 1994 by
Crawford et al.). The expanding fireballs rose to heights exceeding
3000 km above the cloudtops and were briefly seen in visible light by
their own thermal emission (directly showing temperatures of several
thousand K). Spectra of these sites showed that even refractory
elements such as sodium, magnesium, iron, and silicon were vaporized
(and if I interpret my notes properly dissociated into atomic form 
rather than remaining bound into molecules). 

     The dark eject are still visible (at least the major impacts).
The material (still unclear whether of cometary or Jovian origin) has
a vertical extent of hundreds of km, known from (1) imaging through
filters tuned on and off a strong methane absorption wavelength, which
serves as a convenient depth gauge, and (2) obvious parallax against
underlying cloud features as Jupiter rotates. The mass of material
(assuming small particles) is comparable to the estimated impact mass
- I saw no good arguments that this is more than coincidence, though.
It was sobering to see quite directly that each of these impacts could
have more than blanketed the Earth with absorbing material (specially
with our lower surface gravity), since the bigger impact spots spread
over a couple of times Earth's surface area. The transport of the
material would be more complicated here, with the planet's curvature
being a stronger factor. Broad energy considerations (best I can tell)
suggest that little material would reach escape velocity even in a
terrestrial impact. The column density of absorbing material is low by
terrestrial standards (estimated at 5x10^18 atoms/cm^2) but the
integrated absorption of sunlight is rather efficient (as we see,
since the dark spots are so prominent; but recall that we see double
the line-of-sight absorption, since the sunlight we see by and large
passes through the absorbing material once on the way down and once
again on the way up). 

     The rapid winds above the cloudtops (never before directly
measured, by the way) are disrupting the absorbing clouds, but slowly
- at this rate the bigger ones will last for months. Unless the
different atmospheric structures do something I don't see, this is
pretty direct evidence that impacts would produce an absorbing shround
around the Earth of duration at least a year (not even counting
proposed constituents like soot that don't enter on Jupiter). 

There were also interesting effects on the Jovian magnetic field,
though they don't enter for the present purposes  archosaurs migrated
following magnetic field lines (harrumph). New auroral zones were
observed fed by particles released at several impacts, and the radio
emission from Jupiter's radiation belts was pumped up during the
string of impacts. 

The upshot is that, for understanding the effects of any impacts in
terrestrial history, the models for energy release and atmospheric
blanketing don;t seem to have too wide of the mark. Now - is there an
atmospheric physicist out there who can tell us more about how these
phenomena would scale to the terrestrial atmosphere? 

Bill Keel                           Astronomy, University of Alabama

From:	US1RMC::"[email protected]" "MAIL-11 Daemon" 30-AUG-1994 19:38:40.36
CC:	
Subj:	COMET DAY, Santa Fe

Announcing COMET DAY,  Monday, October 17, 1994
HyperVelocity Impact Symposium (HVIS 1994)
Sweeney Convention Center, 201 West Marcy Street, Santa Fe, New Mexico
 
Featuring:

Dr. Eugene Shoemaker, keynote address
"The Crash of Shoemaker-Levy 9 Comet with Jupiter"

Informal poster session.  Presentations by modelers and observers
"Impact on Jupiter: Models and Results"

Technical Sessions on Planetary Impact and Space Debris Shields

Buffet Reception at the Eldorado Hotel

----Special One-Day Registration Fee of $100.00----

For further information and early registration contact

Alita Roach, Los Alamos National Laboratory, MS P915,
 Los Alamos,  New Mexico  87544
Phone: (505) 665-6277, FAX: (505) 665-3407  Email: [email protected]

Lalit Chhabildas, Sandia National Laboratories, MS0821,
 Albuquerque, New Mexico  87123-0821
Phone: (505) 844-4147, FAX: (505) 844-0918  Email: [email protected] 

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% Date: Tue, 30 Aug 1994 15:36:48 +0700
% Errors-To: [email protected]
% Reply-To: [email protected]
% Originator: [email protected]
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% Subject: COMET DAY, Santa Fe
% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US1RMC::"[email protected]" "Ron Baalke"  4-SEP-1994 
To:	[email protected]
CC:	
Subj:	Galileo Begins Sending Back Comet SL9 Data

From the "JPL Universe"
August 26, 1994

Galileo begins sending data from SL9 impacts

   The Galileo spacecraft has begun a six-month process of
radioing to Earth data taken during the collisions of Comet
Shoemaker-Levy 9 at Jupiter in July.

   From its vantage point in space en route to Jupiter, Galileo
had the only direct view of the collisions of comet fragments on
the dark side of the giant planet July 16-22.

   Galileo stored observational data on its onboard tape recorder
and is transmitting them to Earth via its low-gain antenna over
several months.

   Ground controllers initially instructed Galileo to send back
"jail-bar" image strips--narrow slices of various portions of data--
to help them search for the most promising observations on the
spacecraft's tape recorder.

   Preliminary looks at "jail-bar" data recently sent to Earth of
the impact of the comet's fragment K led scientists to confirm
detection of an intense burst of light lasting about 40 seconds.
These data are from a special image frame that was deliberately
smeared during a time exposure to form a streak from Jupiter and
another from the impact flare, providing high resolution in time
and brightness.

   More data from the K event will be sent to Earth in October.

   Other data still stored onboard the spacecraft include images
of the fragment W impact; mission scientists do not yet know
whether the actual impact was captured on these  frames. A small
portion of the fragment W data will be sent to Earth in mid-August
and late September; the rest is scheduled to be received in January.

   Data from the fragment G impact were taken with Galileo's
ultraviolet spectrometer, the infrared mapping spectrometer and
the photopolarimeter. These data will be returned starting in late
September and continuing through December.

   Galileo data primarily of interest to scientists and amateur
astronomers will be posted on an ongoing basis on Internet via the
World Wide Web system. This may be accessed by the public from
JPL's home page, at the address http://www.jpl.nasa.gov/ under the
"News" heading.

From:	US1RMC::"[email protected]" "MAIL-11 Daemon"  8-SEP-1994 09:46:53.47
CC:	
Subj:	SL9 CD-ROM IS READY!

Network Cybernetics Corporation has completed the first CD-ROM on the
Shoemaker-Levy 9 / Jupiter collision.  The disc is an ISO-9660 format
CD-ROM and contains files collected from observatories and other
sources around the world. 

Included are more than 170 megabytes of still images and 45 megabytes
of motion video.  Also includes hundreds of text and Post Script files
related to the impact.  Shareware viewing programs are included for
OS/2, DOS, Macintosh platforms.  Image and video formats include GIF,
TIFF, JPEG, EPS, FITS, MPEG, FLI/FLC, and others. 

SL9: Impact '94 has a list price of $39.00.  We are offering a special
price of $29.00 to sci.astro and sci.space readers for all orders
received before October 31, 1994.  For more information, a complete
press release and ordering information may be obtained by sending
email to: [email protected]. 

 ---------------------------------------  -----------------------------------
| Internet   [email protected]         || Network Cybernetics Corporation   |
| Fidonet    Steve Rainwater@1:124/2206 || Tel 214-650-2002 BBS 214-258-1832 |
| Compuserve 72066,3606                 || Fax 214-650-1929                  |
 ---------------------------------------  -----------------------------------

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% Date: Wed, 7 Sep 1994 23:01:52 -0700
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% X-Comment: Comet P-Shoemaker/Levy 9 Mailing List

From:	US1RMC::"[email protected]" "Ron Baalke" 13-SEP-1994 
To:	[email protected]
CC:	
Subj:	SL9 Home Page Tops 2 Million Accesses

The access count on the JPL Comet Shoemaker-Levy home page went over 2
million mark today.  The second million took a little longer to get to
than the first million - the first million only took 10 days, most of
that during the comet impact week.  The URL for the home page is:

http://newproducts.jpl.nasa.gov/sl9/sl9.html

P.S. New images are still being added to the home page.  

      ___    _____     ___
     /_ /|  /____/ \  /_ /|     Ron Baalke     | [email protected]
     | | | |  __ \ /| | | |     JPL/Telos      | 
  ___| | | | |__) |/  | | |__   Galileo S-Band | If you don't know where you're
 /___| | | |  ___/    | |/__ /| Pasadena, CA   | going, you'll end up somewhere
 |_____|/  |_|/       |_____|/                 | else.   Yogi Berra.

From:	US1RMC::"ASTRO%[email protected]" "Astronomy Discussion 
        List" 14-SEP-1994 15:38:12.19
To:	Multiple recipients of list ASTRO <ASTRO%[email protected]>
CC:	
Subj:	Re: Comet to hit Earth?

   Here's an article that ran in the Sept. 11, 1994 San Jose Mercury News:

   DESTINATION EARTH?

   Newly found comet fragments bear watching, observers say. (Reuters)

   LONDON--Astronomers are carefully observing fragments from a recently
discovered comet that some believe could potentially threaten Earth,
Britain's Sunday Telegraph reported.

   The new comet, known as Machaholz-2, was discovered last month by an
American astronomer as it raced toward the Sun, but as other observers
turned their telescopes toward the object they found the comet had broken
up, just like comet Shoemaker-Levy 9, which hit Jupiter in July.

   By Saturday, five fragments had been seen--all in a path that would
bring them within the orbit of Earth.

   Information from observatories so far suggests that if the fragments
continue on their current trajectory they should avoid an impact with
Earth, but astronomers said it was extremely hard to predict their
long-term behavior.

   Duncan Steel of the Anglo-Australian Observatory told the Telegraph
that the influence of Jupiter would dominate their orbital behavior.
"It's most likely that Jupiter will pick up the objects and throw them
out of the solar system again.  As far as we can tell, they should not 
hit the Earth in the next 100 years.  But we might be wrong."

   "It could happen in the next few decades.  What we need are more
observations so that we can get a more accurate orbit."

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% Date:         Wed, 14 Sep 1994 14:23:24 CDT
% Reply-To: Astronomy Discussion List <ASTRO%[email protected]>
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% Organization: Birmingham Astronomical Society
% Subject:      Re: Comet to hit Earth?
% X-To:         [email protected]
% To: Multiple recipients of list ASTRO <ASTRO%[email protected]>

From:	US1RMC::"[email protected]" "Astronomy Discussion List" 
        19-SEP-1994 16:31:04.27
To:	Multiple recipients of list ASTRO <[email protected]>
CC:	
Subj:	Status of Galileo SL9 Images

Galileo Images of the Shoemaker-Levy 9 Impacts

Clark R. Chapman

The Galileo spacecraft, unlike all near-Earth observatories, had a
direct view of the Shoemaker-Levy 9 impact sites. The solid state
imaging system thus was able to take the only direct pictures of the
impact sites.  As of this writing, very little data has been returned,
but it is sufficient to say that we have detected events K and W. 
Event K lasted about 45 seconds and reached ~10% the brightness of
Jupiter itself; W was visible for at least 5 seconds (that may be a
lower bound) and reached 1% the brightness of Jupiter.  The partial
data returned from N is inconclusive. 

By the end of October, we will have returned all of the data we plan
to return from the spacecraft tape recorder for events N and K, as
well as a very interesting portion of the W data set.  Therefore, by
the time of the AGU meeting, we should be able to characterize these
luminous phenomena in terms of the important phases of the impact
phenomenology -- bolide, fireball, plume, etc.  By merging these data
sets with other data (e.g. HST, ROSAT, groundbased, etc.), it should
be possible to define many important characteristics of the impacts
that would not be possible to infer solely from the groundbased data. 
For example, the total energy deposition, and its rate of deposition
in Jupiter's atmosphere, can be constrained from Galileo data of
prompt phenomena, and thus establish the "initial conditions" for the
subsequent fireball, plume, and spot-creation processes that were so
thoroughly studied from Earth. 

This research has been made possible by special efforts on the part of
the Galileo Project team, and especially by the hard work of Catherine
Heffernan and Ken Klaasen, of J.P.L., who I thank on behalf of Mike
Belton and the SSI Team. 

Sept. 19, 1994.

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From:	US1RMC::"[email protected]" "MAIL-11 Daemon" 22-SEP-1994 20:11:35.47
CC:	
Subj:	More SL9 Images

To: SL9 Mailing List

    I finally manage to put some photos of Jupiter on photo CD.
The images are available at http://isc.tamu.edu/~astro/index.html 
and ftp://seds.lpl.arizona.edu/pub/astro/SL9/images/recent/ALL/tamu*.*
thanks to Chris Lewicki.  These GIF's are amateur photos that I made 
at Texas A&M Observatory using a 14" telescope.  tamu24.gif shows sites 
G/D and L on July 20, 1994.

Dan Bruton
[email protected]

-----------------------------------------------------------------------

Forwarded message:

From:   John R. Spencer
Subj:	Jupiter at T + 2 months

I obtained 1.58 - 5.05 micron infrared images of Jupiter with the
NSFCAM infrared camera at the NASA Infrared Telescope Facility on Mauna
Kea between 4:45 and 5:10 UT on 15 September 1994, nearly two months
after the start of the comet impacts.  I ran through Kevin Baines' set
of CVF wavelengths, though the best images were at the "non-standard"
wavelength of 2.30 microns.  Jupiter central longitude (System III) was
51 - 66 degrees.

At 2.3 microns the impact sites are still the brightest things on the
planet: individual sites are merging into a very lumpy ribbon extending
over all visible longitudes but with relatively little latitude
spread.  Longitudes 340 - 50 are much brighter than 50 - 130, with
strong condensations near 340, 15, and 40 degrees (longitudes System
III, good to about +/- 10 degrees): these may be the remains of the L,
G/D/S, and R sites respectively.  Strangely, the H site. last reported
near longitude 100, is not distinguishable from the faint continuous
ribbon in these images.  More definitive identification of the impact 
sites in these data will require correlation with earlier images.

One of the best images, at 2.30 microns with central longitude 56 
degrees, is available by anonymous ftp from ftp.lowell.edu, 
192.103.11.2, in pub/spencer, as irtf940915.gif, with documentation
in irtf940915.readme

John Spencer, Lowell Observatory.

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