In addition, all of these satellites bear the mark of violence in the form of numerous craters upon their surfaces. Miranda is perhaps the most interesting moon of Uranus. Eventually, scientists claim, the mutual gravitational attraction between the pieces brought them all back together in a jumbled lump of a moon. Ariel is about 1200 km across and has many valleys and scarps covering its surface. Umbriel is comparable in size to Ariel, and it is also the darkest and least geologically active of Uranus' moons.
Titania is among the largest of the moons.
It is assumed that the surface of Titania is extremely old because of the high density of impact craters there. In addition, like Umbriel, bright frost deposits may make some geologic features show up better. Oberon is about the same size as Titania, and it contains many impact craters. Thus, the surface is thought to be very old as well. The result is that one of Uranus' poles will sometimes point towards the Sun for very long periods of time.