Saturn’s moon Iapetus shows its bright (and lumpy!) side in this image from Cassini, taken on November 29. Like many people I know, 914-mile-wide Iapetus has a dark side and a bright side, its bright surface composed of water ice and rock and its dark half a coating of material, most likely from the newly-discovered super-thick ring that surrounds Saturn far beyond the other rings.
As it orbits Saturn in a retrograde – essentially “backwards” – direction, the dark ring material drawn towards a forwards-traveling Iapetus would strike it especially forcefully…”like bugs on a windshield,” as one scientist put it.
This hasn’t been proven yet but the theory makes good sense, especially in light of the new ring discovery, since Iapetus’ dark side is on its leading hemisphere. In other words, it’s definitely driving into a rain of something.
Some of the dark-covered surface can be seen on the lower half of the moon in this view.
Raw image: NASA/JPL/SSI