Meanwhile on the other side of the planet, the other Mars rover, Opportunity, is also finding evidence of water.
Opportunity has spent the past eight months exploring the rim of Victoria Crater, a half-mile (800 meters) wide and 230 feet (70 meters) deep.
(See related photo: "Mars Orbiter Spies Victoria Crater" [October 6, 2006].)
The rover has spotted numerous outcrops of intersecting sandstone layers similar to those found in southern Utah, Squyres said at the Acapulco meeting.
Such deposits represent ancient sand dunes now converted to sandstone.
"You're seeing the preserved remains of ancient Martian sand dunes," Squyres said.
While sand dunes are generally associated with deserts, these formations also reflect ancient water, he said.
The sand is composed of sulfates, which were most likely produced when acidic groundwater dissolved minerals out of ancient rock and brought them to the surface, he explained.
The water then evaporated, leaving sulfate-rich sand that formed the dunes.
The next step for Opportunity, Squyres said, will be to look for a route into the crater for a close-up look at the outcrops.
"If it's safe to go in, we will," he said.
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