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

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-Earth Object 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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