A soil analysis by the Mars rover Spirit strongly suggests that the Red Planet was once wet, providing evidence of conditions that might have supported life, NASA scientists said Monday.

Spirit found soil that is rich in silica, and "the processes that could have produced such a concentrated deposit of silica require the presence of water," it said in a release.

A Mars rover.

The discovery "reinforces the fact that significant amounts of water were present in Mars' past, which continues to spur the hope that we can show that Mars was once habitable and possibly supported life," said Doug McCuistion, director of NASA's Mars exploration program.

"This is a remarkable discovery," said Steve Squyres of Cornell University, principal investigator for the rovers' science instruments. "You could hear people gasp in astonishment."

Spirit did the analysis while exploring a low range of hills named Gusev Crater, where it had found other indicators of water, such as patches of water-bearing soil. The newly discovered patch of soil has been given the informal name "Gertrude Weise," after a player in the All-American Girls Professional Baseball League.

The find was disclosed during a recent teleconference of rover scientists. One revealed that Spirit's alpha particle X-ray spectrometer, a chemical analyzer at the end of the rover's arm, had found that Gertrude Weise was about 90 per cent pure silica.

Spirit worked within about 50 metres of the Gertrude Weise area for more than 18 months before the discovery was made.

Meanwhile, Spirit's twin Opportunity has been exploring Victoria Crater for about eight months.

The two rovers finished their main three-month missions in April 2004. Both are still operating, although showing signs of age.

"One of Spirit's six wheels no longer rotates, so it leaves a deep track as it drags through soil," NASA said.

That exposed patches of soil, leading to discoveries at Gusev, including Gertrude Weise.