The Mars rover Spirit (search) has discovered several layers of rocks in a hilly region of the Red Planet that suggest a wet and violent history in the planet's early life, scientists said Tuesday.
The six-wheeled robot has been examining rocks from three outcrops in the Gusev Crater region that show possible successive deposits of water-altered debris from explosive events.
The debris is most likely ash that settled after volcanic eruptions, scientists said, although they could not rule out the possibility of an impact explosion.
"Once upon a time, Gusev was a pretty violent place. Big, explosive events were happening and there was a lot of water around," said principal investigator Steve Squyres of Cornell University (search).
The findings were presented at the American Geophysical Union (search) meeting in New Orleans. The mission is managed at NASA's Jet Propulsion Laboratory here.
Meanwhile, Spirit's twin rover, Opportunity, is trying to free itself from a sand dune. Opportunity's wheels started slipping April 26 during a planned 295-foot trip. While trying to drive over a foot-high sand dune, the rover stopped moving, its wheels hub-deep in soft soil.
Engineers have managed to move Opportunity (search) about a foot since then, and said it would take at least another week to free it.
Spirit and Opportunity have been exploring opposite sides of Mars since landing in January 2004. Both rovers have long outlasted their primary, three-month missions.