A broken wheel on one of the Nasa rovers that has been roaming Mars for three and a half years has helped scientists to find strong new evidence that the Red Planet was once wetter and possibly capable of supporting life.

Analysis of a patch of soil that was churned up by the stuck wheel on the the Spirit rover has revealed it is composed of about 90 per cent pure silica — a mineral that would have required the presence of water to form.

The find has surprised and delighted researchers, who said it is among the most significant discoveries made by Spirit since it landed on Mars in January 2003.

It adds to growing evidence, amassed by the Nasa rovers and orbiting spacecraft such as Europe’s Mars Express in recent years, that suggest Mars was once much warmer and wetter than it is today, and that it may have harboured life.

Steve Squyres of Cornell University in New York state, who leads the rover team, said: “You could hear people gasp in astonishment.

“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.”

The Spirit rover and its twin, Opportunity, were originally intended to operate for just three months, and though they are still going more than three years after that period they are showing signs of age.

One of Spirit’s six wheels no longer rotates, and thus cuts a deep track as it is dragged through the Martian ground, and this has provided scientists with a serendipitous opportunity to examine the deep-lying soil it has disturbed.

The latest patch was examined using Spirit’s thermal emission spectrometer, which found a high silica content. Minerals of such purity require water to form, and one possible explanation is that it was laid down when volcanic acidic vapours interacted with water at the surface. Another is as a result of hot spring activity.

Steve Ruff of Arizona State University, who leads the thermal emission spectrometer team, said: “We’ve looked at dozens of disturbed soil targets in the rover tracks, and this is the first one that shows a high silica signature.”

The disturbed patch, which lies in the Gusev Crater region of Mars, has been named Gertrude Weise, after a player in the All-American Girls Professional Baseball League.

Doug McCuistion, director of Nasa’s Mars Exploration Programme, said, “This unexpected new discovery is a reminder that Spirit and Opportunity are still doing cutting-edge exploration more than three years into their extended missions. It also reinforces the fact that significant amounts of water were present in Mars’s past, which continues to spur the hope that we can show that Mars was once habitable and possibly supported life.”

David Des Marais, an astrobiologist at Nasa’s Ames Research Centre, in Moffett Field, California, said: “What’s so exciting is that this could tell us about environments that have similarities to places on Earth that are clement for organisms.”

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

Dr Squyres said: “This discovery has driven home to me the value of in-depth, careful exploration. This is a target-rich environment, and it is a good thing we didn’t go hurrying through it.”

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