Radar Helps in Discovery of Dumbbell-Shaped Asteroid

A mile-long asteroid that passed relatively close to Earth last August is actually a two-lobed object that looks something like a dumbbell tumbling through space, photos released Monday reveal.

The asteroid, designated 1989 PB, passed within 2 1/2 million miles of Earth, 11 times farther away than the moon, as it traveled a course that will not bring it that close to this planet again for about half a century.

Using the 1,000-foot radio telescope at Arecibo, Puerto Rico, astronomers from the Jet Propulsion Laboratory and the Harvard-Smithsonian Center for Astrophysics bounced radar waves off the tumbling asteroid, then captured the echo to create 16 radar images of the asteroid.

Although theorists have speculated that some asteroids may consist of more than one lump of material held together by a weak gravitational pull, the scientists expressed surprise that the first image of such a small body would reveal it to be so irregular.

“It is remarkable,” said JPL’s Steven Ostro, leader of the radar astronomy team.

Ostro was joined in the project by Irwin Shapiro of the Harvard-Smithsonian center and Alice Hine of the Arecibo Observatory.

The asteroid, which was discovered by JPL astronomer Eleanor Helin, rotates about once every four hours, the images reveal.

Asteroids are believed to be rocky, frozen remnants of the early solar system. This particular asteroid orbits the sun every 400 days, traveling beyond the orbit of Mars--the next planet out from Earth--and back to the sunward side of Venus, the next planet in from Earth.