NASA’s Opportunity rover has successfully climbed out of Victoria Crater, the gaping basin it has been exploring for nearly a year. Now it will explore the area around the crater, studying rocks thought to have been gouged out of the surface in powerful meteorite impacts.
The crater was deeper than any the rover had explored previously. So scientists studied the rock layers exposed on its walls to trace how the geological conditions that formed each subsequent layer changed over time.
But about a month ago, the rover experienced a spike in the electric current in its left front wheel. A similar current spike had occurred in the right front wheel of Opportunity’s twin, Spirit, a day before the wheel stopped working in 2006.
So mission planners plotted an escape route, deciding to send the rover out of the crater the way it had come in. “We were concerned that any wheel failure on our ageing rover could have left us trapped inside the crater,” said John Callas, project manager for the rovers at NASA’s Jet Propulsion Laboratory in Pasadena, California.
Late on Thursday, the rover drove over the lip of the crater and onto the surrounding plains. “The rover is back on flat ground,” said Paolo Bellutta, an engineer who “drives” the rover from JPL.
Now, the rover will study fist-sized rocks, called cobbles, that litter the plains. These rocks seem to be different in colour and composition from the sandstone thought to form the top few hundred metres of the region’s surface.
The sandstone tends to break apart into dust rather than forming such chunks of rock, says Bruce Banerdt, rover project scientist at JPL. “These are rocks that came from somewhere else,” he told New Scientist earlier this week. “Some are meteorites and others are ejecta from impacts into the local Meridiani plains.”
The rocks may have originated hundreds of kilometres away from where they now lie – thrown there in the violent impacts that ejected them from the Martian surface. Or they may have originated below the region’s sandstone layer. “This will give us insights into other places than we’re sitting on right now – either deeper or off in the distance somewhere,” Banerdt said.
After studying the cobbles, mission planners will have to decide where to send the rover next.
They are eyeing two eroded craters, about the size of Victoria, that lie a couple of kilometres away to the north. Banerdt says the eroded rims of the craters may be made of rocks that were once deep below the surface but were brought upwards in the violence of the impact that formed them.
Alternatively, mission planners may decide to send the rover south of Victoria Crater.
The Meridiani plains where the rover is exploring slope gently from north to south. So moving southward might allow the rover to study rocks from deeper geological layers than are exposed at its current location. “As we move south, we’re moving vertically in a column of rock,” Banerdt said.
If the rover, which was designed to last about three months but has survived on the planet for more than four years, maintains its longevity, the team might send it to a “huge” crater that lies 15 kilometres south of Victoria. “If we last forever,” Banerdt mused. “But nobody really wants to think about that – it’s testing fate a little bit too much.”
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