| Article: 20967
From: [email protected] (Bill Higgins-- Beam Jockey)
Newsgroups: sci.space,sci.astro
Subject: Venus at Lunar and Planetary Science Conference
Date: 13 Mar 92 04:28:41 GMT
Sender: [email protected]
Organization: Fermi National Accelerator Laboratory
I've just seen the program for the Lunar and Planetary Science
Conference, to be held in Houston from 16 through 20 March. For a
couple of thousand planetary scientists, this is the major conference
of the year. I won't be attending, but I can give you a sample of
abstracts of papers to be presented.
DISCLAIMER: Not all interesting papers have abstracts available. Not
all abstracts are guaranteed interesting. I picked a small sample
which I thought might be interesting to readers on the Net, possibly
because they are relevant to discussions we've had here.
Possibly somebody who attends the conference next week can report to
us on any juicy tidbits. I for one would like to hear about the
Gaspra session on Friday!
Thanks to the torrent of data pouring down from the Magellan radar mapper,
Venus is the star of the show this year. This message will cover just
a few Venus-related papers. I've probably shortchanged some good work.
=================================
Solomon S. C.* Smrekar S. E. Bindschadler D. L. Grimm R. E. Kaula W. M.
McGill G. E. Phillips R. J. Saunders R. S. Schubert G. Squyres S. W.
Stofan E. R.
Venus Tectonics: An Overview of Magellan Observations
Now that Magellan images and altimetry are available for more than 90%
of the Venus surface, a global perspective may be taken on the styles
and distribution of lithospheric deformation on Venus and their
implications for the tectonic history of the planet. Tectonic
features on Venus are widespread and diverse, and comparatively few
regions are undeformed. Areas of high relief and steep slopes and the
large fraction of impact craters cut by faults indicate that tectonic
activity on Venus has continued until geologically recent time, and
most likely the planet is tectonically active at present. Compared
with the Earth, horizontal displacements on Venus over the last 400
My have been limited. Unlike the Earth, Venus does not show evidence
for a global system of nearly rigid plates with horizontal dimensions
of 10^3-10^4 km separated by narrow plate boundary zones a few
kilometers to tens of kilometers across. The major tectonic features
are likely the result of lithospheric deformation induced by mantle
convection, but the details of the interaction between lithosphere and
mantle remain to be understood.
Baker V. R.* Komatsu G. Gulick V. C. Kargel J. S.
Venusian Valleys and Channels
More than 200 newly discovered relic valley and channel complexes
occur on Venus, of which the most interesting are classed as canali,
outflow channels, and valley networks. The canali are up to 6800 km
long and characterized by remarkably constant width. Outflow channels
display large-scale landforms indicative of cataclysmic fluid flow.
Valley networks have morphologies similar to those produced by
sapping processes on Mars and Earth. Although water is improbable as
the genetic agent, a waterlike lava behavior seems required to explain
all these observations.
Sjogren W. L.*
Venus Gravity: Status and New Data Acquisitions
Pioneer Venus Orbiter has provided essentially all our present
knowledge of the Venusian gravity field via Doppler radio tracking
data. Recently more analyses and further reductions with these old
data have produced more detailed global fields to support the
navigation and SAR mapping for the Magellan (MGN) spacecraft. High
resolution gravity from MGN has not been acquired to date because
the antenna used for SAR mapping was pointed at Venus during the
period of low altitude. It has to point to earth for gravity data. In
1992 a large new block of very significant gravity data will be
acquired from MGN. There will also be new data from Pioneer Venus
Orbiter since it will end itself with burn up in the Venusian
atmosphere due to the lack of on board fuel in Dec. of 1992.
[If the FY1993 budget cuts Magellan as the White House and NASA
management have proposed, there will be no gravity mapping on the
fourth cycle; this is a source of great controversy, and you can bet
it'll be discussed loudly and long in Houston next week. --WSH]
Gregg T. K. P.* Greeley R.
Formational Constraints on Venusian "Canali"
The discovery of channels on Venus (termed "canali") longer than
Earth's longest river channels is surprising, because liquid water is
unstable at venusian surface conditions. It has been suggested that
superfluid lavas with viscosities of 1 Pa s, such as komatiite,
anhydrous "lunar"-type basalt, carbonatite and sulfur flows, created
the canali by thermally and/or mechanically eroding the pre-flow
surface. However, lava channels may form via constructional processes
as well. Thermal modelling of various lava types at venusian surface
conditions suggests that thermal erosion should be more efficient on
Earth than on Venus, implying that the venusian canali are the
result of mechanical erosion or constructional processes.
Weitz C. M. Moore H. J. Schaber G. G.
Low-Emissivity Impact Craters on Venus
A preliminary analysis of 70 medium- to large-size impact craters on
Venus has shown that 11 of these have crater floors with
emissivities lower than 0.8. The remaining 59 craters have
emissivities between 0.8 to 0.9, independent of the specific
backscatter cross-section of the crater floors. To account for these
low emissivities, we suggest that the floors of these impact craters
have inclusions of conducting particles.
Leff C. Morrison A. D.
The Small Craters of Venus - An Inspection Using Magellan Data
We are mapping and characterizing the small impact craters, single and
multiple, up to and including 6 km diameter on the surface of Venus.
These small craters are more sensitive to surface processes than the
large craters. We have identified and catalogued similar features
among the small craters and noted some of the similarities and
differences between small and large craters. No aeolian mass
transport, parabolic deposits or multiple-ringed small craters were
observed. Craters with distinct central peaks were noted. There are no
apparent impact-related effects on target area structure. The ejecta
patterns indicate that the emplacement of the ejecta materials was by
a process of surface or near-surface gas-borne particle flow. In
about one-third of the craters examined, we observed tectonic
modification subsequent to the impact.
--
O~~* /_) ' / / /_/ ' , , ' ,_ _ \|/
- ~ -~~~~~~~~~~~/_) / / / / / / (_) (_) / / / _\~~~~~~~~~~~zap!
/ \ (_) (_) / | \
| | Bill Higgins Fermi National Accelerator Laboratory
\ / Bitnet: [email protected]
- - Internet: [email protected]
~ SPAN/Hepnet: 43011::HIGGINS
Article: 20968
From: [email protected] (Bill Higgins-- Beam Jockey)
Newsgroups: sci.space,sci.astro
Subject: Other worlds at Lunar and Planetary Science Conference
Date: 13 Mar 92 04:30:23 GMT
Sender: [email protected]
Organization: Fermi National Accelerator Laboratory
I've just seen the program for the Lunar and Planetary Science
Conference, to be held in Houston from 16 through 20 March. For a
couple of thousand planetary scientists, this is the major conference
of the year. I won't be attending, but I can give you a sample of
abstracts of papers to be presented.
DISCLAIMER: Not all interesting papers have abstracts available. Not
all abstracts are guaranteed interesting. I picked a small sample
which I thought might be interesting to readers on the Net, possibly
because they are relevant to discussions we've had here.
Possibly somebody who attends the conference next week can report to
us on any juicy tidbits. I for one would like to hear about the
Gaspra session on Friday!
Though my selection doesn't reflect it, there are *major* amounts of
meteorite and cosmic-dust work in the program. I may have skimped on
other specialties too (I see our pal Peter Ford of MIT has been
radar-mapping the Moon). But at least you can get some of the flavor
of the LPSC from my postings.
=================================
Wolszczan A.*
Discovery of Planets Around a Millisecond Pulsar
Two planet-sized bodies orbiting a 6.2-ms pulsar PSR1257+12 have been
detected with the 305-m Arecibo radio telescope using a pulse timing
method. Orbital periods of the two planets are 66.6 days and 98.2 days
- close to a 3/2 resonance. The orbits have small but significant
eccentricities of ~0.02. The corresponding planetary masses and
distances from the central neutron star are 3.4 Earth masses, 2.8
Earth masses, and 0.36 AU, 0.47 AU, respectively. The planets could
have condensed out of a disk of matter ablated by the pulsar's high
energy radiation from its former stellar companion. An existence of a
third planet in the 1257+12 system with Earth-like mass and orbital
parameters is indicated by a significant discrepancy between timing
and VLA--derived positions of the pulsar.
Mustard J. F. Head J. W. Murchie S. M. Pieters C. M. Belton M. S.
McEwen A. S.
Schickard Cryptomare: Interaction Between Orientale Ejecta and
Pre-Basin Mare from Spectral Mixture Analysis of Galileo SSI Data
There is abundant evidence for pre-Orientale mare volcanism in the
region of the Schiller and Schickard impact structures, south of the
Humorum Basin. Analyses of recently acquired Galileo SSI images
determined that the Schiller-Schickard region (2-4 x 1OO,OOO km^2)
exhibits an enhanced mafic content over typical highlands. In this
analysis, SSI data are used to map the proportions of mare, highland,
and fresh crater spectral components to determine the extent of
pre-Orientale volcanism and to investigate the dynamics of basin
ejecta emplacement. A linear spectral mixture model is used to map the
spatial extent and abundance of mare, highland, and fresh craters. The
mare abundance image is examined in detail and a minimum areal extent
of pre-Orientale mare of 3-4 x 1OO,OOO km^2 is determined. The
proportion of basin ejecta to mare target material decreases as a
function of radial distance from the rim of Orientale. This is
consistent with the systematics expected for a ballistic erosion model
for ejecta emplacement, but may also reflect a decrease in the amount
of basin ejecta with radial distance in the discontinuous ejecta facies.
[SSI is "Solid State Imager." Did you see the cover of the 31 January
1992 issue of *Science*? There's another article summarizing what
Galileo's imaging team learned from comparing color variations on the
Moon to telescopic and sample-return data. --WSH]
Swindle T. D. Burkland M. K. Johnson J. R. Larson S. M. Morris R. V.
Rizk B. Singer R. B.
Systematic Variations in Solar Wind Fluence with Lunar Location:
Implications for Abundances of Solar-Wind-Implanted Volatiles
Geometric effects, including shielding by Earth's magnetotail, produce
systematic variations in the solar wind fluence with lunar location.
We have calculated what those variations are and combined them with
maps of Ti abundance to produce estimates of He-3 abundance. However,
if all exposed grain surfaces are saturated at Apollo-level fluences,
fluence variations will not lead to elemental abundance variations.
This proposition can be tested by analysis of Soviet Luna samples.
Costard F. M. Achache J. Bibring J. P. Blanc M. Coutin-Faye S.
Langevin Y. Lognonne P. Masson P. Moura D. Rocard F.
Mars Rover Mission: The French Views
With a potential view to future cooperations with the United States,
Russia, and the European Space Agency (ESA) in the forthcoming
exploration missions, the French Space Agency (CNES) has initiated in
1989 the "Automatic Planetary Rover" program. In that framework, a
scientific committee has been settled to define the scientific
requirement for Mars exploration missions involving mobile vehicles.
This paper summarizes the work of this committee. The rover will
contribute to the deployment of fixed stations, either isolated or
part of a local or regional network. During its traverses, the rover
will perform geophysical profiling of the main planetary fields and
realize vertical soundings (electromagnetic and radar measurements)
over distances on the order of few hundred kilometers. The rover will
also be used as a mobile surface laboratory having the capabilities
for selection, acquisition, and analysis of samples.
Sunshine J. M.* Pieters C. M. Head J. W. McEwen A. S. Greeley R.
Oceanus Procellarum as Viewed by Galileo: Evidence for Compositional
Diversity in the Mare Deposits and at the Marius Hills Plateau
New Galileo multispectral images of the western nearside and parts of
the farside of the Moon lend a synoptic perspective to the study of
maria and volcanic complexes in Oceanus Procellarum. The coverage
includes deposits along the western edge of Procellarum, which are
located on the limb when viewed from Earth. UV/VIS ratios are
consistent with previous studies and indicate great diversity in the
TiO2 content of the maria. Analysis of the VIS/IR ratio indicates that
most basalt units along the western edge of Procellarum have a
generally weaker overall mafic absorption than those in the interior
of Procellarum. However, their spectral affinities to the eastern
maria suggest that the deposits in central Procellarum and Imbrium,
i.e., the Flamsteed Basalts, are unusually mafic-rich, and perhaps
even ultramafic in composition. Galileo also offers a regional
overview of the Marius Hills plateau. The plateau itself shows a
distinctly low value in the VIS/IR ratio suggesting a lower mafic
content, while some areas on the plateau have even lower VIS/IR
ratios. Specific correlations with volcanic features will be examined
to determine if the compositional data and the morphology might, in
fact, be indicative of differentiated volcanism.
Maurette M. Brownlee D. E.* Joswiak D. J. Sutton S. R.
Antarctic Micrometeorites Smaller than 50 Micrometers
Using refined collection techniques, Antarctic micrometeorites in the
25-50-micrometer size range were collected for the first time on the
1991 Euromet expedition. Analysis of these samples by SEM and
Synchrotrom XRF techniques indicates that they are similar to the
hydrated classes of stratospheric micrometeorites except for lower
abundances of S and Ni. The low Ni abundances indicate either that
the small Antarctic particles are intrinsically different from their
stratospheric cousins or that Ni depletion occurs during atmospheric
entry or residence in Antarctic ice. These Antarctic particles,
although more thermally altered than the 1O-micrometer particles
collected in the stratosphere, are an important resource for future
investigation of asteroid and comet dust reaching Earth.
See T. H.* Mack K. S. Warren J. L. Zolensky M. E.
Continued Investigation of the Impact Flux on the Long Duration Exposure
Facility by the Meteoroid and Debris Special Investigation Group
The Meteoroid and Debris Special Investigation Group has continued its
efforts to define the hypervelocity particle environment in LEO by
conducting high-resolution scans of various pieces of LDEF hardware.
This effort uses the cratering densities for craters between 50 and
1000 micrometers in diameter, as well as the penetration-hole
densities for perforations >5 and >=1000 micrometers in diameter to
define the particle environment witnessed by the LDEF spacecraft.
Difference in the production rates for the cratering and
penetration-hole densities from the leading to trailing edge of LDEF
range from as low as 8:1, and to as high as 50:1.
McDonnell J. A. M.*
LDEF's Space Exposure Yields Hypervelocity Impact Penetration Relationships
LDEF's 5.75 years of exposure to the LEO space environment has yielded
a wealth of hypervelocity impact features on differing target
materials and configurations. The paper presents sample data from the
University of Kent's Microabrasion Experiment (MAP AO 023) and other
sources yields comparison and summary properties of the incident
particulate distribution and hypervelocity impact parameters.
Cave J. A.*
Martian Volcanoes and Ground-Ice: Evidence for the Localised
Enrichment of Sub-Surface Ice by Juvenile Volatiles
The results of crater analyses and a landform survey have been used to
construct a comprehensive account of the distribution and importance
of water within the Elysium region. Evidence of a widespread
ground-ice has been obtained. The ice-distribution is shown to be
strongly dependent upon latitude, though its concentration varies
with depth and is strongly influenced by geological setting. Important
differences have been detected in the distribution of Southern
Highland and Northern Lowland ground-ice. In addition, the ice is
enriched at depth in the Elysium Lavas, and nearer to the surface to
the north-west of Elysium Mons. The apparent distribution suggests
that several ice-emplacement mechanisms have operated on Mars,
including the enrichment of the deeper ice by juvenile water from
beneath the Elysium volcanic province.
Butler B. Muhlemann D. Slade M.
A Comparison of the Radar Returns from the Icy Poles and Other Regions
of Mars and Mercury
The first full disk radar images of the planet Mercury were obtained
during the inferior conjunction in August of 1991. Approximately 77%
of the surface was imaged, at resolutions as good as 140 km. At the
time of the observations, the north pole was visible, and the most
prominent feature in the images is at the nominal polar position.
Because of the signal strength and polarization characteristics, we
interpret the north polar feature to be due to ices. Due to the
reduced value of the reflectivity when compared to the south polar
residual ice cap on Mars, we think that the ices are either
significantly contaminated, covered over by a layer of absorbing
material, or areal coverage is not complete. Other prominent features
on the unphotographed side correspond closely to positions where
enhanced atmospheric sodium and potassium have been measured from
earth. This may indicate that these locations are large basins similar
to the Caloris impact basin, where enhanced atmospheric volatiles
may be the result of enhanced degassing in the disrupted surface and
near surface. No areas were imaged that resembled the "stealth" area
on Mars.
Sotin C. Smrekar S. Rosenqvist Y. Bibring J.-P.
Topography of Tharsis Mons (Mars) Deduced from the ISM Experiment:
Comparison with Radar Profiles
Nine infrared images of the surface of Mars were obtained in 1989 by
the ISM experiment onboard the Phobos 2 spacecraft. The measurement of
the absorption depth of C02 at the 2 micrometer absorption band and
a model for the vertical distribution of pressure and temperature of
the Martian atmosphere allow the determination of the altimetry with
a resolution of 150 m. ISM altimetry is compared with radar profiles
obtained at the Goldstone observatory. A reasonnable agreement is
found between the two data sets. We are presently examining the
compensation of Ascraeus and Pavonis Montes with the ISM altimetry and
Viking altimetry and topography data, using ORBSIM program.
Gurley J. G. Cheng R. K.
VEER: Countermeasures Against the Threat of Asteroid Impact
VEER is a concept for countering the threat of Earth-impacting
asteroids, with the following elements: a vigorous program to
increase the rate of discovery of Earth-crossing asteroids and to
extend the lower limit on the size of catalogued objects; a series of
robotic missions to near-Earth objects in order to better characterize
their physical properties; precursor missions to any objects
identified as threatening to strike the Earth within a few decades;
and a negation mission against any imminent threat. A safe miss
distance of 5 Earth radii can be achieved by a nuclear device producing
a crater whose diameter is on the order of 0.2 times the asteroid
diameter, detonated 10 to 20 years before the encounter with Earth.
=================================
O~~* /_) ' / / /_/ ' , , ' ,_ _ \|/
- ~ -~~~~~~~~~~~/_) / / / / / / (_) (_) / / / _\~~~~~~~~~~~zap!
/ \ (_) (_) / | \
| | Bill Higgins Fermi National Accelerator Laboratory
\ / Bitnet: [email protected]
- - Internet: [email protected]
~ SPAN/Hepnet: 43011::HIGGINS
|