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Subj: [ASTRO] NEW EXTRA-SOLAR PLANET DISCOVERED! Its circular orbit suggests it formed like planets in the Solar System.
April 24, 1997
NEW EXTRA-SOLAR PLANET DISCOVERED; CIRCULAR ORBIT SUGGESTS
IT FORMED LIKE PLANETS IN OUR SOLAR SYSTEM
CAMBRIDGE, MA -- The notion that giant, Jupiter-like bodies may be a common
occurrence around stars like the Sun has been bolstered by the discovery of
such an object orbiting Rho Coronae Borealis, a star in the constellation
Northern Crown. The newly discovered planet offers additional evidence for
how such systems form, and bolsters the idea that other worlds like our own
may be widespread throughout the galaxy.
The discovery was made by a team of scientists from three institutions -- the
Smithsonian Institution's Astrophysical Observatory (SAO) in Cambridge, MA,
the National Center for Atmospheric Research (NCAR) in Boulder, CO, and the
Pennsylvania State University in State College, PA -- based on observations
made at the Smithsonian's Fred Lawrence Whipple Observatory on Mt. Hopkins,
Arizona.
The scientific team includes Sylvain Korzennik, Martin Krockenberger, Peter
Nisenson, and Robert Noyes of SAO; Harvard University graduate student
Saurabh Jha; Timothy Brown and Edward Kennelly of NCAR; and Scott Horner of
Penn State.
Using a special instrument known as the Advanced Fiber Optic Echelle (AFOE)
spectrograph located at the 1.5-meter Tillinghast Reflector of the Whipple
Observatory, the scientists detected extremely small variations in the
recession velocity of Rho Coronae Borealis that are thought to be caused by
the presence of an orbiting companion.
With the AFOE capable of measuring velocity variations smaller than 10
meters per second (about 22 miles per hour), the scientists found that the
speed of Rho Coronae Borealis varied back and forth by about 67 meters per
second, or 150 miles per hour, over a 40-day period. This led the team to
conclude that the star has a companion in a 40-day orbit and, from the size
of the velocity variation and the mass of the star (almost identical to the
Sun), they calculated that the companion must be slightly more massive than
the planet Jupiter.
The short orbital period means the planet must lie only about 1/4 of an
Astronomical Unit from the star -- closer than Mercury orbits the Sun (an AU
is the distance of the Earth from the Sun). This also implies its
temperature would be about 300 degrees C, or more than 500 degrees F --
much too hot for liquid water to exist, and hence not a likely place for life to
form.
According to the researchers, the circular nature of the orbit suggests that
the planet was formed like the planets in our own solar system, that is,
through the slow coalescence of dust and gas from the circularly rotating
disk that is thought to surround all newborn stars. A more eccentric, or
highly elliptical orbit, could imply that the companion object was a failed
star, the unsuccessful second partner in a potential binary star system.
"This discovery helps show that giant planets like Jupiter may be reasonably
common around ordinary stars," says Robert Noyes of SAO. "Moreover, they can
be found at a variety of distances from their parent stars, ranging from
very close in, like the companion to 51 Pegasi, to very far away, like
Jupiter relative to the Sun. The planet around Rho Coronae Borealis, like
several others, is in between.
"It is exciting to think that there may be many smaller planets much more
like the Earth in orbit around these stars, as in our own Solar System,"
says Noyes.
Timothy Brown, of NCAR, carried out the design and fabrication of the AFOE
spectrograph's optics. He added, "All the giant planets found so far orbit
Sun-like stars. The star Rho Coronae Borealis is another one of these, but
it appears to be about 10 billion years old -- twice as old as the Sun."
Scott Horner, of Penn State, designed and built the AFOE's iodine cell (a
precise velocity-reference device). "It was the star's solar similarity that
led us to target it for study in the first place," he agreed. "Soon after we
began to look at it, we thought that its radial velocity was varying. Now,
after 11 months of monitoring, we're sure."
As one of the stars forming the "crown" of the constellation, Rho Coronae
Borealis is visible from February through September to naked-eye observers
in the Northern Hemisphere . It is about 50 light years from Earth.
A scientific paper describing the discovery has been accepted for
publication in the Astrophysical Journal Letters. A pre-publication version
of the paper has also been made available, along with other details about
the AFOE program, on the World-Wide Web at http://cfa-www.harvard.edu/afoe.
NCAR is sponsored by the National Science Foundation.
For more information, contact:
James Cornell, Public Affairs, SAO -- 617-495-7462;
[email protected]
Anatta, Public Affairs, NCAR --303-497-8604;
[email protected]
Barbara Kennedy, College Communications, Penn State -- 814-863-4682;
[email protected]
Figure available upon request from SAO Public Affairs, 617-495-7461; or, as
an anonymous ftp at: ftp://cfa-ftp.harvard.edu/pub/afoe/np.ps
Caption:
Graphic representation of variations in the velocity of the star Rho Coronae
Borealis observed at the Smithsonian Institution's Whipple Observatory in
Arizona, showing a 40-day period indicative of a Jupiter-sized companion.
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