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MSNBC:

An unexplained phenomenon akin to a space-borne car wash has boosted the performance of one of the two U.S. rovers probing the surface of Mars, New Scientist magazine said on Tuesday. It said something -- or someone -- had regularly cleaned layers of dust from the solar panels of the Mars Opportunity vehicle while it was closed down during the Martian night.

Via Instapundit who will apparently allow the Martians to squeegee his Passat but not his RX-8.