Weak Mars Rover Struggling to Find Winter Haven
Now you see it, now you don't.
Recent storms covered the Mars rover Spirit with such a thick layer of dust (top) that it nearly blended into the Martian soil in this "self-portrait" compiled from images taken between October 26 and 29, 2007. By comparison, the rover was still shining bright (bottom) after two years on the red planet in an August 27, 2005, composite image.
Severely weakened by the dust storms, solar-powered Spirit now has just two weeks to find a suitable place to weather the dark Martian winter, NASA officials have announced.
Images courtesy NASA/JPL-Caltech/Cornell
Richard A. Lovett in San Francisco, California
for National Geographic News
December 11, 2007
With the long Martian winter closing in, the weakened NASA rover Spirit is searching for a haven to weather the planet's most severe season.
The rover, now exploring a geological feature known as Home Plate, has about two weeks to find a suitable winter hideout, scientists announced yesterday.
The giant dust storm that dimmed the Martian skies last summer did more than temporarily cut down the rover's supply of sunlight. It also deposited a thick film of dust on Spirit's solar panels.
"We are at 42 percent efficiency right now," John Callas of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, said during a press briefing at the American Geophysical Union's fall meeting in San Francisco.
"The rover has so much dust on it, it's almost completely camouflaged," he added.
That makes it difficult for the robot to generate power for critical systems as the sun dips lower.
Scientists want to park the rover on a slope angling about 25 degrees toward the sun, but even that solution is risky.
"That will give us significantly lower daily energy than either rover has ever experienced before," Callas said.
NASA's other Mars rover, Opportunity, is currently exploring Victoria Crater.
Christmas Deadline
With a dangerously low amount of power, Spirit can only be driven every other day, with a rest day to recharge its batteries.
"We need to be in position by Christmas," Callas said. "[We] … have about seven more drive days left."
Possible rest stops for the rover are nearby on the northern edge of Home Plate, and scientists have a couple places in mind, he said. (See a Mars map.)
Once in position, the rover will idle as sunlight declines until the middle of the Martian winter next June. Meanwhile, more dust is likely to accumulate on its panels.
"We won't be doing much, and more dust [than we expect] could make that dicey," Callas said.
Still, the scientists have a few tricks up their sleeve. Shutting down a heater to one of the scientific instruments would cut the amount of power needed for bare-minimum survival by about a third.
A riskier action would be turning down the heat on the rover's electronics.
Spirit's processors are able to work at temperatures as low as -40 degrees Fahrenheit (-40 degrees Celsius), but they might be able to go lower.
"We've tested them to -67 degrees Fahrenheit [-55 degrees Celsius] in ground testing before launch," Callas said.
"But that was a brand-new rover, and this one's four years old. We'd be taking a risk."
Plenty of Power for Opportunity
The other rover, Opportunity, faces no such crisis.
That's because it is closer to the Martian equator, where sunlight is more consistent across seasons, said Steve Squyres of Cornell University, who heads Opportunity's science team. (See a photo of the crater.)
Also, Opportunity's solar panels are much more frequently cleaned by wind gusts, he added. At Spirit's position near Home Plate, panel-scouring winds are rare.
"Opportunity is going to die someday, but it's not going to be from dust on the panels," Squyres said.
If Spirit's solar panels hold out through the winter, it too might bring another year's worth of discoveries.
Other than the dust, Callas of JPL said, "both rovers are in very good health. We have had no major [equipment] failures since we lost the right front wheel on Spirit almost two years ago."
