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| discovered = July 8, 1979 | mean_orbit_radius = | eccentricity = | period = (7 h, 9.5 min) | avg_speed = 31.378 km/s | inclination = 0.03° (to Jupiter's equator) | satellite_of = Jupiter | mean_radius = | dimensions = 20 × 16 × 14 km | volume = | mass = | density = 0.86 g/cm³ (assumed) | surface_grav = (0.0004 ''g'') | escape_velocity = ≈ 0.008 km/s | rotation = synchronous | axial_tilt = zero | albedo = | single_temperature = ≈ 122 K }} Adrastea ( ; (ギリシア語:Αδράστεια)), also known as , is the second by distance, and the smallest of the four inner moons of Jupiter. It was discovered in ''Voyager 2'' probe photographs taken in 1979, making it the first natural satellite to be discovered from images taken by an interplanetary spacecraft, rather than through a telescope. It was officially named after the mythological Adrasteia, foster mother of the Greek god Zeus—the equivalent of the Roman god Jupiter. Adrastea is one of the few moons in the Solar System known to orbit its planet in less than the length of that planet's day. It orbits at the edge of Jupiter's Main Ring and is thought to be the main contributor of material to the Rings of Jupiter. Despite observations made in the 1990s by the Galileo spacecraft, very little is known about the moon's physical characteristics other than its size and the fact that it is tidally locked to Jupiter. == Discovery and observations == Adrastea was discovered by David C. Jewitt and G. Edward Danielson in ''Voyager 2'' probe photographs taken on July 8, 1979, and received the designation . Although it appeared only as a dot, it was the first moon to be discovered by an interplanetary spacecraft. Soon after its discovery, two other of the inner moons of Jupiter (Thebe and Metis) were observed in the images taken a few months earlier by ''Voyager 1''. The ''Galileo'' spacecraft was able to determine the moon's shape in 1998, but the images remain poor. In 1983, Adrastea was officially named after the Greek nymph Adrastea, the daughter of Zeus and his lover Ananke. 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「Adrastea (moon)」の詳細全文を読む スポンサード リンク
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