Two scientists propose an explanation for the bizarre ridge belting Saturn's moon Iapetus at the equator. At one time Iapetus itself may have had a satellite, created by a giant impact with another body. The satellite's orbit, would have decayed because of tidal interactions with Iapetus, and at some point it would have been ripped apart, forming a ring of debris around Iapetus that would eventually slam into the moon near its equator.

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