Oberon is the outermost of the main satellites on the planet Uranus. It is the second largest and most massive and the ninth most massive in the Solar System. Discovered by William Herschel in 1787, Oberon gets its name from a character in English literature. Its orbit is partially outside of Uranus' magnetosphere. Oberon is made up of roughly equal parts of ice and rock that are probably differentiated into a rocky core and an ice sheet. There may be a layer of liquid water at the boundary between the core and the mantle. The Oberon surface, which is dark and slightly reddish in color, appears to have been shaped by the impact of asteroids and comets. It is covered by numerous impact craters that reach diameters of more than 200 km. Oberón has a system of canyons and scarps formed by the expansion of its interior at an early stage of its evolution. This satellite was probably formed from the accretion disk that surrounded Uranus after the formation of the planet.
