After spending 160 days traversing a plain and climbing a steep hill, the Mars explorer Spirit is finding the first strong indications of significant quantities of water at Gusev Crater.
Spirit's twin, Opportunity, has found powerful evidence of water halfway around Mars in Meridiani Planum. Both NASA craft have been exploring the planet since January.
After a complicated climb to an altitude of about 30 feet in the Columbia Hills, Spirit is now parked at an outcrop of bedrock called Longhorn that shows strong signs of weathering by water. The key feature of Longhorn, said principal investigator Steven Squyres of Cornell University, is the presence of two kinds of rocks: "some gray, others light-toned, crumbly and cruddy."
Squyres suspects that the rocks represent a "before and after" pair. The gray rocks appear to be relatively pristine, whereas the lighter ones have undergone some kind of alteration. The most likely cause is the action of water, he said.
"This is different from the rocks out on the plain," Squyres said. "Here we have a more thorough, deeper alteration, suggesting much more water."
So far, however, investigators have determined the composition of only the "after" rocks. The team used the rover's rock abrasion tool to drill a hole into a rock's interior.
"This is one of the softest rocks we have encountered" on Mars, said geologist Doug Ming of the Johnson Space Center. It also has high concentrations of sulfur, chlorine and bromine, possibly deposited by water.
Opportunity, meanwhile, has descended about 30 feet into the small Endurance Crater in Meridiani Planum and is encountering unusual rocks as well.
Meridiani Planum is littered with large numbers of small, round rocks that the team has called blueberries.
But now the craft has encountered some similar stones that are also round, but are lighter and redder. The stones are very coarse and rough, unlike the smoother blueberries, and are more irregular in shape. Some appear to have blueberries inside them.