A patch of bright-toned Martian soil analyzed by NASA's rover Spirit is so rich in silica that it may provide some of the strongest evidence yet that ancient Mars was much wetter than it is now, U.S. medias reported Tuesday.

The alpha particle X-ray spectrometer, a chemical analyzer at the end of Spirit's arm, had measured a composition of about 90 percent pure silica for this soil. The processes that could have produced such a concentrated deposit of silica require the presence of water, according to NASA's Mars Rover Project scientists.

"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," said Steve Squyres, principal investigator for the Mars rovers' science instruments.

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

"This is some of the best evidence Spirit has found for water at Gusev," said Albert Yen, a geochemist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

One possible origin for the silica could have been interaction of soil with acid vapors produced by volcanic activity in the presence of water. Another could have been from water in a hot spring environment.

The latest discovery adds compelling new evidence for ancient conditions that might have been favorable for life, according to members of the rover science team.