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| discovery = yes | discoverer = William Lassell | discovered = October 10, 1846 | semimajor = | eccentricity = 〔 | period = (retrograde)〔〔 | avg_speed = 4.39 km/s | inclination = 129.812° (to the ecliptic) 156.885° (to Neptune's equator)〔〔 129.608° (to Neptune's orbit) | satellite_of = Neptune | physical_characteristics = yes | mean_radius = 〔 (0.2122 Earths) | surface_area = 〔 | volume = 〔 | mass = ()〔 | density = 〔 | surface_grav = () (0.48 Moons)〔 | escape_velocity = 〔 | sidereal_day = 5 d, 21 h, 2 min, 53 s〔 | rotation = synchronous | axial_tilt = 0 | albedo = 0.76〔 | magnitude = 13.47〔 | abs_magnitude = −1.2〔 | single_temperature = 38 K (−235.1° C〔 | atmosphere = yes | surface_pressure = 1.4–1.9 Pa〔 (1/ the surface pressure on Earth)〔 | atmosphere_composition = nitrogen; methane traces.〔 }} Triton is the largest natural satellite of the planet Neptune. It was discovered on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the opposite direction to its planet's rotation.〔 At in diameter, it is the seventh-largest moon in the Solar System. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been a dwarf planet captured from the Kuiper belt.〔 Triton has a surface of mostly frozen nitrogen, a mostly water-ice crust,〔 an icy mantle and a substantial core of rock and metal.〔 The core makes up two-thirds of its total mass. Triton has a mean density of 〔 and is composed of approximately 15–35% water ice.〔 Triton is one of the few moons in the Solar System known to be geologically active. As a consequence, its surface is relatively young, with a complex geological history revealed in intricate cryovolcanic and tectonic terrains.〔 Part of its crust is dotted with geysers thought to erupt nitrogen.〔 Triton has a tenuous nitrogen atmosphere less than 1/70,000 the pressure of Earth's atmosphere at sea level.〔 == Discovery and naming == Triton was discovered by British astronomer William Lassell on October 10, 1846,〔 just 17 days after the discovery of Neptune. A brewer by trade, Lassell began making mirrors for his amateur telescope in 1820. When John Herschel received news of Neptune's discovery, he wrote to Lassell suggesting he search for possible moons. Lassell did so and discovered Triton eight days later.〔〔 Lassell also claimed to have discovered rings. Although Neptune was later confirmed to have rings, they are so faint and dark that it is doubtful that he actually saw them.〔 Triton is named after the Greek sea god Triton (Τρίτων), the son of Poseidon (the Greek god comparable to the Roman Neptune). The name was first proposed by Camille Flammarion in his 1880 book ''Astronomie Populaire'',〔 and was officially adopted many decades later.〔 Until the discovery of the second moon Nereid in 1949, Triton was commonly referred to as "the satellite of Neptune". Lassell did not name his own discovery; he later successfully suggested the name Hyperion, previously chosen by John Herschel, for the eighth moon of Saturn when he discovered it.〔 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「Triton (moon)」の詳細全文を読む スポンサード リンク
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