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1993-05-03
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PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
Contact: Diane Ainsworth
FOR IMMEDIATE RELEASE December 3, 1991
Astronomers at Jet Propulsion Laboratory are tracking a
small object, probably no larger than 10 yards, that is hurtling
through space and will pass near the Earth at a distance of about
288,000 miles on Dec. 5.
"Although the object, identified as Object 1991 VG, is
probably a tiny asteroid whose orbit is very Earth-like, we
initially considered the possibility that it had been an aging
spacecraft returning to Earth," said JPL astronomer Dr. Donald
Yeomans, who is part of a new center at the Laboratory designated
as NASA's International Center for Near-Earth Objects.
"A recent reconstruction of its orbital history suggests the
object was never launched from Earth and, hence, is a natural
solar system object," Yeomans said.
Astronomers from the Steward Observatory on Kitt Peak near
Tucson, Ariz., have been watching the object since it was
discovered by the Spacewatch Telescope on Nov. 6.
The JPL team of astronomers will spend the next week trying
to improve predictions of where the object will be in mid-
December, when an attempt will be made to bounce radar off the
object. If they are provided with enough observations from
astronomers in the Southern Hemisphere by then, the team will be
able to use radar facilities at NASA's Goldstone Deep Space
1
Network complex in Mojave, Calif., and the Arecibo radar antenna
in Puerto Rico, for the experiment.
The radar-bounce experiment will help them determine the
object's physical nature, as well as its origin and future
orbital path. The radar experiment would be led by JPL
astronomer Dr. Steven J. Ostro, who determined that the asteroid
1989 PB (now numbered and named 4769 Castalia) had a strange,
double-lobed shape.
"This newly discovered object is probably a tiny asteroid
orbiting the sun in a period just over one year," Yeomans said.
"A close Earth approach of this type is not an unusual event. On
average, an object of this size passes closer than the lunar
distance to Earth once every few days. Only recently has the
optical technology been used to spot these small asteroids."
The mysterious object poses no threat to Earth, Yeomans
said. Closest approach will occur at 1:45 a.m. Pacific Standard
Time just outside the lunar distance of 464,000 kilometers
(288,000 miles). Even if the object was found to be on a
collision course with Earth sometime in the distant future, it
probably would not be expected to survive its entry into Earth's
atmosphere.
JPL has been active in the discovery and physical
characterization of near-Earth-approaching objects. A program of
discovery, the Palomar Planet-Crossing Asteroid Survey, directed
by JPL astronomer Eleanor Helin, has been responsible for nearly
half the discoveries of near-Earth asteroids to date.
The Laboratory is currently establishing a new Near-EarthObject Watch to coordinate observations of these objects,
including their closest approaches to Earth. This coordinated
effort will alert observers to new discoveries and provide them
with enough information to plan the most effective follow-up
observations.
"There has been an emerging realization that there are
hundreds of thousands of these small objects, at least 10 yards
in size, circling the sun and passing close to Earth," Yeomans
said. "These near-Earth objects are the building blocks from
which the planets formed. They also represent the source of
relatively large objects that could one day strike the Earth and
directly influence the evolution of Earth's atmosphere and
biosphere.
"Because of their low surface gravity and proximity to
Earth," he added, "these scientifically important objects also
offer us the most accessible source of raw materials for future
structures built in space."
Observing campaigns will be encouraged through the new Near-
Earth Object Watch at JPL to monitor these objects during their
closest approaches to Earth. Coordinated observing campaigns
will also be encouraged for those asteroids singled out as
attractive future mission targets.
The new Near-Earth Object Watch will be managed by the Jet
Propulsion Laboratory for NASA's Office of Space Science and
Applications.
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#1406
12/03/91 dea JPL-PIO