NASA's Spirit Mars rover imperiled by dust storms

Massive Martian dust storms are threatening the survival of NASA's Spirit rover, which has been exploring Mars for five years but is now dangerously low on power.

Spirit last communicated with Earth on Sunday, when it reported that its solar arrays had produced just 89 watt-hours of energy, which is much less energy than the rover uses in a day.

It's also the least power that either Spirit, or its twin, Opportunity, has produced over the entire life of the mission, which began in 2004.

John Callas, the rover project manager at the Jet Propulsion Laboratory in La Cañada Flintridge, said the rover's survival might be in jeopardy because the dusty arrays were producing only a third as much power as they were capable of, even before the latest dust storms hit. The storms of the last few days have reduced the output even more to 26.5%, he said.

The announcement of Spirit's problems came only a day after NASA declared an end to the Phoenix mission to Mars' north pole, the first to sample ice on an alien planet. Dust storms, and the approach of winter in the northern hemisphere, were blamed for Phoenix's demise.

As for Spirit, Callas said he believed that the low power levels probably tripped a built-in fault-protection system, which automatically disconnects nearly all the rover's electronics from its batteries to keep them from draining completely. When that happens, mission managers on Earth lose control of the vehicle.

Ideally, after a low-power trip, the rover will periodically check to see whether the batteries have recharged. If they have, it resumes normal operations.

"The best chance for survival for Spirit," Callas said, is to avoid a low-power trip, from which the rover might not awake. To avoid draining the batteries, mission managers sent a message to the rover today, ordering it not to communicate with Earth until Thursday.

By then, NASA officials hope, the dust storms will have cleared and the solar panels will be producing more power.

After spending much of the southern hemisphere winter parked, Spirit had only started driving again when the dust storms hit. The rover is currently halted at a geological feature called Home Plate. Meanwhile, Opportunity, which has not been compromised by the dust storms to the same extent, is driving to a deep crater.

During their nearly five years on Mars, the rovers have drilled into rocks and snapped pictures of erosion patterns that proved that large parts of the Red Planet were once covered by standing seas or lakes. Today, the surface is much too cold for water to be in liquid form, scientists say.

Scientists are now using the rovers to understand how the planet changed from a more temperate beach-side world to a barren rock.

Johnson is a Times staff writer.

john.johnson@latimes.com