This close-up image of Saturn's moon Iapetus was taken by NASA's Cassini spacecraft. It shows the moon's bright, icy surface and mysterious dark patches. The dark material is believed to have come from some of Saturn's other moons. It was probably blasted away from the other moons by meteor impacts where it was deposited over time on top of the native, bright surface. Iapetus has a very low density, so it is probably composed mainly of water ice with a small amount of rocky material mixed in.
NASA / JPL / Space Science Institute