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The folks at NASA's Jet Propulsion Lab in Pasadena, CA, would very much like to thank whoever -- or whatever -- cleaned the solar panels on the Mars rover Opportunity. They just don't know who to thank.

For some odd reason, the panels on Opportunity are suddenly much cleaner than the panels of its twin rover, Spirit. At first, both rovers suffered a gradual drop of power. When they landed back in January, the panels on both rovers put out about 900 watt/hours each day. Spirit's solar cells now produce only 400 watt/hours a day. So did Opportunity's -- until about six months ago. That's when scientists on the ground started noticing the power was slowly increasing again on Opportunity.

But here's the odd thing: Whatever cleaned Opportunity's panels continued to clean them. At this point, its solar cells are putting out just a bit more than 900 watt/hours a day.

Dr. Steve Squyres of Cornell University, head of the Mars team at JPL, told ANN Thursday he thinks the wind is cleaning and recleaning the panels.

Whatever the reason, Rover team leader Jim Erikson knows enough not to look a gift horse in the mouth. "These exciting and unexplained cleaning events have kept Opportunity in really great shape," he told New Scientist Magazine.

It's a little spooky... and a little like Geppetto's workshop in the story of Pinocchio. Opportunity goes to sleep during the Martian night. At least four times, when it was awakened by its Earthbound masters, the rover's power output jumped by at least five percent.

There could be another reason for the unexplained cleaning and the difference in power output between the two machines. While Spirit has been working on a relatively flat plain, Opportunity has been exploring a crater. Its panels have, therefore, been tilted to some degree. That might have caused any accumulated dust to simply slide off the panels.

There's a simple way to tell, according to Erikson. He told New Scientist Opportunity rolled out of the crater earlier this month. "If in three or four months Opportunity is still operating and hasn't had another power boost that would suggest the crater was the key," he said.

FMI: http://marsrovers.jpl.nasa.gov/home/