National Aeronautics and Space Administration scientists say a concentrated deposit of silica found by the rover would have required the presence of water.

Members of the rover science team heard from a colleague during a recent teleconference that the rover's alpha particle X-ray spectrometer measured a composition of about 90 percent pure silica.

"You could hear people gasp in astonishment," said Steve Squyres of Cornell University, principal investigator for the Mars rovers' science instruments. "This is a remarkable discovery. And the fact that we found something this new and different after nearly 1,200 days on Mars makes it even more remarkable. It makes you wonder what else is still out there."

Exploring a low range of hills inside a Connecticut-sized basin called Gusev Crater, Spirit previously found other indicators of long-ago water at the site, including patches of water-bearing, sulfur-rich soil; alteration of minerals; and evidence of explosive volcanism.