The silica-rich soil uncovered by Spirit's wheel

Credit: NASA

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SYDNEY: A broken wheel on the ageing Mars rover Spirit has unearthed a fresh clue that Mars may once have been wet enough to support life.

The rover, developed by U.S. space agency NASA, discovered a patch of soil that was made up of about 90 per cent pure silica – a composition that would have required the presence of water to form.

Doug McCuiston, director of NASA's Mars Exploration Program, said that 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."

Unusual soil spectrum

The patch of silicate-rich soil was uncovered accidentally after one of the rover's wheels jammed, leaving deep tracks as it dragged across the Martian surface. That churning has exposed several patches of bright soil, leading to some of Spirit's biggest discoveries at the site – including this recent find.

A highly sensitive alpha particle X-ray spectrometer fitted on the rover's arm was used to analyse the soil content as it probed a low range of hills inside the Gusev Crater. The soil's spectrum revealed an unusually high silica content.

"This is a remarkable discovery," said Steve Squyres of Cornell University in Ithaca, New York. "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."

Spirit had earlier gleaned clues that water had once flowed at the site, including patches of water-bearing, sulfur-rich soil and evidence of explosive volcanic activity.

Silica forms in water

According to NASA, one possible origin for the silica could have been interaction of the soil with acid vapours produced by volcanic activity in the presence of water. Another possibility is that the silica formed in reactions that occurred in water in a hot spring environment.

Malcolm Walter, an astrobiologist at Macquarie University in Sydney said the soil patch is reminiscent of Yellowstone National Park, or Roturua in New Zealand, where silica is leached out of rock by hot water, and precipitates to the surface. "It's astounding actually, that there should be a silica rich area like that," he said. "It's very significant, and suggests a very sharp target for looking at life on Mars."

Spirit and its twin rover Opportunity completed their original three-month missions in April 2004. Both are still operating, though showing signs of age.

NASA has laid out plans for further study of the silica-rich soil patch and surrounding deposits unearthed by Spirit. Meanwhile, Opportunity has spent the last eight months exploring Victoria Crater on the opposite side of the Red Planet.