Occasionally, one of my friends will ask me. "Whatever happened to those rovers you guys sent up to Mars?" And I get to respond, "Oh, they're still running around!" And if you've not kept up, the reason for the battery longevity turned out to be the Martian winds, in the form of dust devils.
And it gradually began to dawn on the Earth-bound rover operators what was happening: wind from the passing dust devils was blowing away any dust that had accumulated on the solar panels, giving the rovers a new lease on life with each passage.