The Dark (and Light) Side of the Moon (Iapetus)

I have always been fascinated by Saturn's moon Iapetus since I read the Arthur C. Clarke novel 2001: A Space Odyssey. One side of the moon is significantly brighter than the other. After the Cassini probe passed by, scientists now think that some planetary event caused ice on one side of the moon to evaporate, exposing the dark surface below. This in turn caused more ice to melt due to a temperature differential, until half the surface was bare, dark rock.
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