Deimos

Deimos is the smaller of the two Martian moons and it is shaped like a potato. The largest crater on Deimos is approximately 2.3 km in diameter. Although both of Mars' moons are heavily cratered, Deimos has a smoother appearance because many of its craters are partially filled. When an impact hits, dust and debris are blasted off the surface of the moon, which does not have enough gravitational pull to retain the ejecta. But the gravity of Mars holds onto this debris in a ring around the planet, in approximately the same region that Deimos orbits. As the moon moves through the ring, the debris is redeposited as a dusty layer on its surface.