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1996-01-17
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EMBARGOED UNTIL: 8:30 a.m. CST, January 17, 1996
CONTACT: Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410-338-4514, villard@stsci.edu)
Dr. Christopher Burrows
Space Telescope Science Institute, Baltimore, MD
(Phone: 410-516-6562)
PRESS RELEASE NO.: STScI-PR96-02
DISK AROUND STAR MAY BE WARPED BY UNSEEN PLANET
NASA's Hubble Space Telescope has provided strong evidence for the
existence of a roughly Jupiter-sized planet orbiting the star Beta
Pictoris.
Detailed Hubble images of the inner region of the 200-billion mile
diameter dust disk encircling the star reveal an unexpected warp.
Researchers say the warp can be best explained as caused by the
gravitational pull of an unseen planet.
The suspected planet would dwell within a five-billion mile wide clear
zone in the center of the disk. This zone has long been suspected of
harboring planets that swept it clear of debris, but the Hubble
discovery provides more definitive evidence that a planet is there.
(Alternative theories suggest the clear zone is empty because it is too
warm for ice particles to exist.)
"We were surprised to find that the innermost region of the disk is
orbiting in a different plane from the rest of the disk," says Chris
Burrows (Space Telescope Science Institute, Baltimore, Maryland, and
the European Space Agency) who is presenting his results at the meeting
of the American Astronomical Society in San Antonio, Texas. As he
analyzed Hubble images, taken in January 1995 with the Wide Field
Planetary Camera 2, Burrows discovered an unusual bulge in the nearly
edge-on disk, which was mirrored on the other side of the star. "Such
a warp cannot last for very long," says Burrows. "This means that
something is still twisting the disk and keeping out of a basic flat
shape."
"The presence of the warp is strong though indirect evidence for the
existence of planets in this system. If Beta Pictoris had a solar
system like ours, it would produce a warp like the one we see." Burrows
concludes, "The Beta Pictoris system seems to contain at least one
planet not too dissimilar from Jupiter in size and orbit. Rocky
planets like Earth might circle Beta Pictoris as well. However, there
is no evidence for these yet. Any planet will be at least a billion-
times fainter than the star, and presently impossible to view directly,
even with Hubble."
An alterative explanation of the warp is that the disk could have been
perturbed by a passing star However this is very unlikely because only
the inner region of the disk is affected. Burrows estimates that there
is a one in 400,000 chance for Beta Pictoris to have such a close
encounter with another star. "Though Beta Pictoris is probably at least
100 million years old, other explanations for the warp do not allow it
to last for very long."
The size of the warp allows Burrows to roughly measure the mass of the
orbiting body. "It must lie well within the warp, probably within the
clear zone that exists around Beta Pictoris." On the other hand, he
points out, it cannot be too close to the star because its
gravitational pull would cause the star to "jiggle," and such radial
velocity variations have never been seen in Beta Pictoris.
Burrows estimates the planet is from one-twentieth to twenty times the
mass of Jupiter. The planet must lie within the range of distances
typical of planetary distances within our solar system -- from about
Earth's distance from the Sun to about Pluto's distance from the Sun
(Pluto is roughly 30 times father from the Sun than Earth.)
If the suspected planet were as far from Beta Pictoris as Jupiter is
from our Sun, it also would have about the same mass as Jupiter. The
planet's orbit must be inclined by about three degrees to the plane of
the Beta Pictoris disk, and this is typical of the inclinations of the
orbits of the planets in our solar system.
The star is located 50 light-years away in the southern constellation
Pictor (Painter's Easel). Though its precise age is not known, Beta
Pictoris is generally considered a mature, main sequence star, slightly
hotter than our Sun.
Detections of substellar objects orbiting nearby stars have recently
been reported for two other normal (i.e., main sequence) stars --
Gliese 229 and 51 Pegasus. However, Beta Pictoris is the only
candidate that looks like it might possess a planetary system similar
to our own.
Beta Pictoris also is the only known star with a circumstellar disk of
gas and dust that can be optically imaged. Despite the presence of
dust around approximately one-third of the brightest nearby stars -- as
deduced from NASA's Infrared Astronomy Satellite (IRAS) data --
ground-based telescope imaging has not detected other disks.
Several Hubble programs are currently in progress to search for these
disks. The NICMOS (Near Infrared Camera and Multi-Object
Spectrometer), to be installed on Hubble during the February 1997
servicing mission, will provide a near-infrared capability needed for
this type of search.
* * * * *
The Space Telescope Science Institute is operated by the Association
of Universities for Research in Astronomy, Inc. (AURA), for NASA,
under contract with the Goddard Space Flight Center, Greenbelt, MD.
The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA).
Image files in GIF and JPEG format and captions may be accessed
on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo.
GIF JPEG
PRC96-02 Beta Pic gif/BetaPicB.gif jpeg/BetaPicB.jpg
Higher resolution digital versions (300dpi JPEG) of the release
photographs will be available temorarily in /pubinfo/hrtemp:
96-02.jpg. GIF and JPEG images, captions and press release text are
available via World Wide Web at URL
http://www.stsci.edu/pubinfo/PR/96/02.html, or
http://www.stsci.edu/pubinfo/Latest.html and
http://www.stsci.edu/pubinfo/Pictures.html.
Space Telescope Science Institute press release text and other
information are available automatically by sending e-mail to
listserv@stsci.edu. In the body of the message (not the subject line)
type the words subscribe pio Your Name. Don't use user/account names;
i.e. someone named Jane Doe would type subscribe pio Jane Doe. The
system will reply with a confirmation of the subscription. E-mail
will be received with new releases.