New York: NASA's Mars Exploration rover Opportunity is driving out of a giant crater nearly a year after descending into it to examine exposed ancient rock layers, the American space agency has announced.

"We have done everything. We entered Victoria Crater to do and more," said Bruce Banerdt, of NASA's Jet Propulsion Laboratory in Pasadena, California. Banerdt is project scientist for Opportunity and its rover twin, Spirit. Having completed its job in the crater, Opportunity is now preparing to inspect loose cobbles on the plains.

Some of these rocks, approximately fist-size and larger, were thrown long distances when objects hitting Mars blasted craters deeper than Victoria into the Red Planet. Opportunity has driven past scores of cobbles but examined only a few.

"Our experience tells us there is lots of diversity among the cobbles," said Scott McLennan of the State University of New York, Stony Brook. McLennan is a long-term planning leader for the rover science team. "We want to get a better characterisation of them. A statistical sampling from examining more of them will be important for understanding the geology of the area." Opportunity entered Victoria Crater on September 11, 2007,after a year of scouting from the rim.

Once a drivable inner slope was identified, the rover used contact instruments on its robotic arm to inspect the composition and textures of accessible layers. The rover then drove close to the base of a cliff called "Cape Verde," part of the crater rim, to capture detailed images of a stack of layers 20 feet tall. The information Opportunity has returned about the layers in Victoria suggest the sediments were deposited by wind and then altered by groundwater.

Source : PTI