Article Posted on : - Aug 27, 2008

CALIFORNIA (BNS): NASA's Mars Exploration Rover Opportunity is heading back to the Red Planet's surrounding plains, nearly a year after descending into a large Martian crater, to examine exposed ancient rock layers.

"We've done everything, we entered Victoria Crater to do and more," said Bruce Banerdt, of NASA's Jet Propulsion Laboratory in Pasadena, Calif. 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's 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,” McLennan said.

Opportunity entered Victoria Crater on Sept. 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’ to capture detailed images of a stack of layers 20 feet tall. The information Opportunity returned, about the layers in Victoria, suggests the sediments were deposited by wind and then altered by groundwater.

The University of New York scientist said, "The patterns broadly resemble what we saw at the smaller craters Opportunity explored earlier." McLennan said that by looking deeper into the layering, they were looking farther back in time. The crater stretches approximately half a mile in diameter and is deeper than any other seen by Opportunity.

Engineers are programming Opportunity to climb out of the crater at the same place it entered. A spike in electric current drawn by Rover's left front wheel in July settled discussions on whether to try to edge closer to the base of Cape Verde on a steep slope. The spike resembled one seen on Spirit when Rover lost the use of its right front wheel in 2006. Opportunity's six wheels are all still working after 10 times more use than they were designed to perform, but the team took the spike in current as a reminder that one could quit.

Expressing his views, Rover Mission manager, Bill Nelson of JPL said, "If Opportunity was driving with only five wheels, like Spirit, it probably would never get out of Victoria Crater." Nelson said that from the experience with Spirit even if Opportunity lost the use of a wheel after it was out on the level ground, mobility could not have been a problem.

Opportunity now drives with its robotic arm out of the stowed position. A shoulder motor has degraded over the years to the point where the Rover team chose not to risk having it stop working while the arm is stowed on a hook. If the motor were to stop working with the arm unstowed, the arm would remain usable.

Spirit has resumed observations after surviving the harshest weeks of southern Martian winter. The Rover won't move from its winter haven until the amount of solar energy available to it increases a few months from now. The Rover has completed half of a full-circle colour panorama from its sun-facing location on the north edge of a low plateau called ‘Home Plate’.

"Both Rovers show signs of aging, but they are both still capable of exciting exploration and scientific discovery," said JPL's John Callas, project manager for Spirit and Opportunity. The team's plan for future months is to drive Spirit south of Home Plate to an area where the Rover last year found some bright, silica-rich soil. This could be possible evidence of effects of hot water.