When the rimwall of Iapetus’s Malun crater broke off and plunged more than five miles to the crater floor, it surged an astonishing 22 miles out from the base of the wall before finally coming to rest. WUSTL planetary scientists speculate that steep topography on the ice moon allows the ice to pick up enough speed to become slippery, even though temperatures on Iapetus are in liquid-nitrogen territory. Credit: NASA/JPL/Space Science Institute