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FOR IMMEDIATE RELEASE		November 20, 1989

	Radar astronomers at the Jet Propulsion Laboratory (JPL),
the Harvard-Smithsonian Center for Astrophysics and the Arecibo
Observatory obtained images of a newly-discovered asteroid as it
passed near the Earth in late August, revealing a two-part form. 
These are the first views of the surface of a small asteroid.
	The images show an irregular double body about a mile long,
rotating like a propeller about every four hours.  Theorists have
speculated that some asteroids could consist of two (or more)
bodies of similar size pulled together by their weak mutual
gravity.  "It is remarkable that the first images of a planetary
body this small should show a double-lobed object," said JPL's
Dr. Steven Ostro, leader of the radar astronomy team.
	The asteroid, designated 1989 PB, came within 2 1/2 million
miles of Earth (eleven times as far as the Moon) in late August,
a few days after the radar observing sessions. 
 	It had been discovered August 9 by JPL optical astronomer
Eleanor Helin and her associates, working at the Palomar
Observatory; Helin quickly alerted the radar team so that their
observations, conducted at the Arecibo Observatory's 1,000-foot
radar/radio telescope in Puerto Rico, could be made in the close pass.


	Orbiting the Sun about every 400 days, 1989 PB travels from
beyond the orbit of Mars to a zone between Venus and Mercury and
back.  Although the asteroid passes near Earth's orbit
frequently, it will not come within several million miles of our
planet again for about half a century.
	Both the radar and the optical observations were part of the
Planetary Astronomy Program of NASA's Office of Space Science and
Applications.  The Arecibo Observatory is part of the National
Astronomy and Ionosphere Center, operated by Cornell University
for the National Science Foundation.  The radar team included Dr.
John Chandler and Dr. Irwin Shapiro of the Harvard-Smithsonian
Center for Astrophysics and Alice Hine of Arecibo Observatory.
	Planetary radar astronomy, which has been used to study the
Moon and the inner planets and, more recently, many asteroids and
outer-planet satellites, is very different from optical
techniques.  While planets and asteroids are seen through the
optical telescope in reflected sunlight (and asteroids look like
tiny points at best), radar provides its own calibrated
illumination, permitting precise measurement of range and motion
from many small reflecting elements of the object.  Computer
processing can turn these data into a two-dimensional image.
	These first images of 1989 PB have picture elements less
than 1,000 feet across, comparing favorably with typical Voyager
spacecraft images, Ostro said. "Within a few months, he added,
"detailed analyses will let us reconstruct the asteroid's three-
dimensional shape, make some statements about how tightly gravity
is holding the two lobes together, and begin to formulatetheories about how it was formed."
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