Scientists work to free Mars rover

The long-lived Mars rover Spirit is stuck in the sand on Mars, and controllers at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., are scrambling to extricate the vehicle before it becomes entombed on the Red Planet.

"This is quite serious," said JPL's John Callas, project manager for Spirit and its twin, Opportunity. "Spirit is in a very difficult situation. We are proceeding methodically and cautiously. It may be weeks before we try moving Spirit again."

The rover, which landed on Mars in 2004 for a three-month mission that has reached five years, was driving toward a pair of volcanic features named Von Braun and Goddard when it became ensnared by soft sand. Over the past few days, controllers at JPL have tried to free the vehicle, but its wheels have just sunk deeper into the ground.

Making the process more difficult, only five of Spirit's six wheels are operable, due to a mechanical problem that occurred three years ago. Callas said project scientists are concerned that all the efforts put into liberating the rover may have dug it so deeply into the sand that its belly pan is now resting on the Martian surface.

That would make it harder for the wheels to gain the necessary traction to escape its predicament, Callas said.

Callas said engineers have stopped trying to drive Spirit for now. Instead they will attempt to replicate the rover's plight in what is known as the "sandbox," a lab at JPL where scientists try to simulate conditions on Mars.

"We're looking at re-landscaping the sandbox to recreate the situation," he said. "We can't send anyone to Mars (to fix the problem), so we're bringing Mars to Earth."

For Spirit, this is the latest in a season of problems. A few weeks ago, it suffered a series of memory lapses that engineers have been trying to diagnose ever since.

The only good news of late has been the series of siroccos that cleaned the dusty surface of the rover's solar panels. So Spirit will have plenty of power available when, or should, engineers come up with a strategy that frees the rover.

Callas said the situation might not be life-threatening to the robot. If the rover is unable to move, it could still perform some science, at least until winter arrives, when the sun is low on the horizon.

Whenever they die, Spirit and Opportunity will be regarded as among the most successful instruments NASA has ever built. Besides outlasting every prediction for longevity, they conducted numerous experiments that helped to clarify Mars' watery history. The rovers found that the Martian surface once had standing, shallow inland seas.