The first known landslides on an asteroid have been spotted on Eros, a 20-mile- (32-kilometer-) long, potato-shaped space rock that is providing new clues about the formation of the solar system and the birth of planets. The NEAR-Shoemaker spacecraft, which has orbited Eros since Valentines Day, has also determined the asteroid is not a huge rubble pile, but is solid rock with a surface layer of rubble created by numerous collisions early in its 4.6 billion-year history.

The collisions pocked Eros with craters, cracked it to produce ridges and grooves, and made landslides tumble down steep slopes.

The asteroids mass is one-billionth that of Earths, and its gravity thousands of times less powerful. Nevertheless, the gravity is strong enough to pull landslides downhill and keep the rubble from flying into space as Eros rotates once every 5.27 hours.

Those are among findings of the first published studies from the Near Earth Asteroid Rendezvous- (NEAR-) Shoemaker spacecrafts $224 million mission to Eros. The studies, conducted by dozens of scientists using NEARs camera and instruments, were printed September 22 in the journal Science. NEAR-Shoemaker, named for late planetary geologist Gene Shoemaker, is the first spacecraft to rendezvous with an asteroid instead of flying past.

NEARs discoveries at Eros are "helping us define the record of how the solar system and the planets formed," said Maria Zuber, a planetary scientist at the Massachusetts Institute of Technology.