Washington: Clay minerals, rocks that usually form when water is present in them for long periods, cover a larger portion of Mars than previously thought.
James Wray, assistant professor at the Georgia Institute of Technology and his team, say clay was in some of the rocks studied by Opportunity when it landed at Eagle Crater on Mars in 2004.
The rover only detected acidic sulphates and has since driven about 22 miles to Endeavour Crater, an area on the planet Wray pinpointed for clay in 2009, the journal Geophysical Research Letters said.
The project, which was led by Eldar Noe Dobrea of the Georgia`s Planetary Science Institute, identified the clay minerals using a spectroscopic analysis from the Mars Reconnaissance Orbiter.
The research shows that clay also exists in the Meridiani plains that Opportunity rolled over as it trekked toward its current position, according to a Georgia Institute statement.
"It`s not a surprise that Opportunity didn`t find clay while exploring," said Wray. "We didn`t know they existed on Mars until after the rover arrived. Opportunity doesn`t have the same tools that have proven so effective for detecting clays from orbit."
"It was also surprising to find clay in geologically younger terrain than the sulphates," said Dobrea. Current theories of Martian geological history suggest that clays, a product of aqueous alteration, actually formed early on when the planet`s waters were more alkaline.
As the water acidified due to volcanism, the dominant alteration mineralogy became sulphates. "This forces us to rethink our current hypotheses of the history of water on Mars," he added.