Seventeen moons of Uranus are known so far. Most of them were actually only discovered by the Voyager space probe.
Two of the satellites are "shepherds", guarding the debris that makes up the outer ring of Uranus. The last two moons were only discovered in 1997. They are believed to have been asteroids that entered the field of gravitation of the planet, where they are held today.
The most interesting of the Uranus moons are the larger satellites that are also visible from the Earth. They were named Miranda, Ariel, Umbriel, Titania and Oberon. Miranda orbits the planet at a distance of 130,000 kilometers and has a diameter of 480 kilometers. Its surface shows deep gorges and large craters.
Ariel has an icy surface featuring a network of long cracks, some of them 30 kilometers deep. There are very few craters. They appear to have been destroyed only recently by increased volcanic activity. Next to Ariel is Umbriel at a distance of approximately 270,000 kilometers from the planet. It is the darkest of all Uranus' moons.
Umbriel is covered in numerous craters. Its most distinguishing feature is a bright ring-shaped crater named Wunda with a diameter of 110 kilometers.
At 1610 kilometers in diameter, Titania is the largest of the satellites of Uranus. Its surface features several long gorges with edges that are probably covered in ice.
The outermost moon of Uranus is Oberon. It is nearly as large as Titania and orbits Uranus at a distance of 585,000 kilometers.
Astronomers believe that the larger satellites of Uranus were at some stage expanded by the gravitational_forces of the planet and subsequently compacted. Only Umbriel escaped these enormous forces.
