NASA/JPL/US Geological Survey
A closeup of a rock outcrop on Mars' Meridiani Planum. Scientists say the texture and composition of the rocks in this region suggests it was once drenched in water.
NASA says it's found new evidence that water may have once flowed on the Red Planet. Scientists studying samples of rock analyzed by the Mars rover Opportunity say they see chemical signs of contact with water. NPR's Joe Palca reports.