Washington, August 27 : NASA's Mars Exploration rover Opportunity is heading back out to the Red Planet's surrounding plains nearly a year after descending into a large Martian crater to examine exposed ancient rock layers.
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 suggests that the sediments were deposited by wind and then altered by groundwater.
"The patterns broadly resemble what we saw at the smaller craters Opportunity explored earlier," said Scott McLennan of the State University of New York, Stony Brook. "By looking deeper into the layering, we are looking farther back in time," he added.
The crater stretches approximately a half 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.
"If Opportunity were driving with only five wheels, like Spirit, it probably would never get out of Victoria Crater," said JPL's Bill Nelson, a rover mission manager.
"We also know from experience with Spirit that if Opportunity were to lose the use of a wheel after it is out on the level ground, mobility should not be a problem," he added.
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.