How Meteoroids Built Iapetus' Mountain Ridge

The mountain ridge on Iapetus has been a mystery since 2004. New simulations suggest it formed from rocky debris falling at shallow angles, which would allow for material to move down range and clump up into a continuous mountain range. (Credit: NASA/JPL/Space Science Institute) Moons in the solar system come in many different forms. Some are boulder-sized, while one is larger than the planet Mercury. Some are mixtures of rock and iron, while others hide oceans and rocky cores under icy surfaces. Two even look a bit like walnuts, each hosting a bulge of material around its equator. Interestingly, both of these, Iapetus and Pan, orbit Saturn. And had I written this post a month ago, “two” would have been “one.” Scientists discovered March 8 that Saturn’s tiny satellite Pan has a ridge. But the other walnut-shaped moon, Iapetus, has puzzled scientists for centuries. The first astronomers who observed Iapetus ...