Umbriel (moon) that obliterated its older surface. Covered by numerous impact craters reaching in diameter, Umbriel is the second most heavily cratered satellite of Uranus after Oberon. The most prominent surface feature is a ring of bright material on the floor of Wunda crater. This moon, like all moons of Uranus, probably formed from an accretion disk that surrounded the planet just after its formation. The Uranian system has been studied up close only once, by the spacecraft "Voyager 2" in January 1986. It took several images of Umbriel, which allowed mapping of about 40% of the moon’s surface. Umbriel, along with
Oberon (moon) Oberon is the second largest and most massive of the Uranian moons after Titania, and the ninth most massive moon in the Solar System. Oberon's density of 1.63 g/cm³, which is higher than the typical density of Saturn's satellites, indicates that it consists of roughly equal proportions of water ice and a dense non-ice component. The latter could be made of rock and carbonaceous material including heavy organic compounds. The presence of water ice is supported by spectroscopic observations, which have revealed crystalline water ice on the surface of the moon. Water ice absorption bands are stronger on Oberon's trailing