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Oberon, also designated , is the outermost major moon of the planet Uranus. It is the second-largest and second most massive of the Uranian moons, and the ninth most massive moon in the Solar System. Discovered by William Herschel in 1787, Oberon is named after the mythical king of the fairies who appears as a character in Shakespeare's ''A Midsummer Night's Dream''. Its orbit lies partially outside Uranus's magnetosphere. It is likely that Oberon formed from the accretion disk that surrounded Uranus just after the planet's formation. The moon consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. A layer of liquid water may be present at the boundary between the mantle and the core. The surface of Oberon, which is dark and slightly red in color, appears to have been primarily shaped by asteroid and comet impacts. It is covered by numerous impact craters reaching 210 km in diameter. Oberon possesses a system of ''chasmata'' (graben or scarps) formed during crustal extension as a result of the expansion of its interior during its early evolution. The Uranian system has been studied up close only once: the spacecraft ''Voyager 2'' took several images of Oberon in January 1986, allowing 40% of the moon's surface to be mapped. == Discovery and naming == Oberon was discovered by William Herschel on January 11, 1787; on the same day he discovered Uranus's largest moon, Titania.〔〔 He later reported the discoveries of four more satellites,〔 although they were subsequently revealed as spurious.〔 For nearly fifty years following their discovery, Titania and Oberon would not be observed by any instrument other than William Herschel's,〔 although the moon can be seen from Earth with a present-day high-end amateur telescope.〔 All of the moons of Uranus are named after characters created by William Shakespeare or Alexander Pope. The name Oberon was derived from Oberon, the King of the Fairies in ''A Midsummer Night's Dream''.〔 The names of all four satellites of Uranus then known were suggested by Herschel's son John in 1852, at the request of William Lassell,〔 who had discovered the other two moons, Ariel and Umbriel, the year before.〔 The adjectival form of the name is ''Oberonian,'' .〔 Oberon was initially referred to as "the second satellite of Uranus", and in 1848 was given the designation by William Lassell,〔 although he sometimes used William Herschel's numbering (where Titania and Oberon are II and IV).〔 In 1851 Lassell eventually numbered all four known satellites in order of their distance from the planet by Roman numerals, and since then Oberon has been designated .〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Oberon (moon)」の詳細全文を読む スポンサード リンク
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