NASA Trying to Free Rover

The Mars rover Opportunity is facing its biggest challenge since it landed last year: how to get out of a sand dune where it’s been stuck for two weeks.

NASA engineers spent this week simulating the Martian terrain at the Jet Propulsion Laboratory in La Canada Flintridge to figure out why the robot got bogged down and how to get it moving again. Engineers performed several tests driving a dummy rover over a mock sand dune.

Scientists sent the first new driving directions to Opportunity on Wednesday, commanding it to start inching down the dune in a series of mini-drives.

The six-wheeled Opportunity had driven about 130 feet of a 295-foot trip when its wheels started to slip April 26. The rover, going backward at the time, eventually stopped -- its wheels stuck hub deep in fine soil while trying to drive over a foot-high dune.

“Mars gives us surprises on a regular basis -- some major, some minor,” project manager Jim Erickson said.

“This is something we consider a major one.”

Meanwhile, the rover has been taking pictures of its surroundings at the edge of an area known as the “etched terrain,” where scientists believe they will find rocks exposed by the gentle erosion of wind.

Opportunity and its twin, Spirit, have been exploring opposite sides of Mars since landing in January 2004 and have uncovered geologic evidence of past water activity. Both rovers long ago outlasted their primary, three-month missions.

This is not the first time a rover has encountered a wheel problem. In June 2004, Spirit’s right front wheel became balky. Spirit overcame the problem by driving in reverse, allowing it to drag the faulty wheel while driving itself with its five other wheels.