Saturn's "Walnut" Moon Mystery Cracked?
"Mind boggling" forces formed odd equatorial ridge, experts suggest.
In general, moons that form around planets—rather than those believed to be captured objects—spin due to the motion of debris as it consolidates into a larger orbiting body.
Unlike Saturn's other spherical or ellipsoid moons, Iapetus has a unique, slightly squashed shape with an 8-mile-high (13-kilometer-high) mountain range running around much of its middle, like the cusp where the halves of a walnut shell join.
(Related: "Saturn's Largest Moon Has Ingredients for Life?")
Previous theories had suggested this odd ridge formed via plate tectonics or volcanoes. Those models tended to produce a broader "ridge zone" rather than a single narrow feature, noted co-author Mikhail Kreslavsky of the