Hydra (moon)
Moon of Pluto / From Wikipedia, the free encyclopedia
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Hydra is a natural satellite of Pluto, with a diameter of approximately 51 km (32 mi) across its longest dimension.[6] It is the second-largest moon of Pluto, being slightly larger than Nix. Hydra was discovered along with Nix by astronomers using the Hubble Space Telescope on 15 May 2005,[1] and was named after the Hydra, the nine-headed underworld serpent in Greek mythology.[14] By distance, Hydra is the fifth and outermost moon of Pluto, orbiting beyond Pluto's fourth moon Kerberos.[11]
Discovery[1] | |
---|---|
Discovered by | Hubble Space Telescope |
Discovery date | 15 May 2005 |
Designations | |
Designation | Pluto III[1] |
Pronunciation | /ˈhaɪdrə/[2] |
Named after | Lernaean Hydra |
S/2005 P 1 | |
Adjectives | Hydrian[3] /ˈhaɪdriən/[4] |
Orbital characteristics[5] | |
64738±3 km | |
Eccentricity | 0.005862±0.000025 |
38.20177±0.00003 d | |
Inclination | 0.242°±0.005° |
Satellite of | Pluto |
Physical characteristics | |
Dimensions | 50.9 km × 36.1 km × 30.9 km[6] (Geometric mean of 38 km) |
Mass | (3.01±0.30)×1016 kg[7]: 10 |
Mean density | 1.220±0.150 g/cm3[7]: 10 |
0.00520055269 g[8] | |
0.4295 d (10.31 h)[9] (July 2015) | |
110°[10] | |
Albedo | 0.83 ± 0.08 (geometric)[11] |
Temperature | 23 K[12] |
22.9–23.3 (measured)[13] |
Hydra has a highly reflective surface caused by the presence of water ice, similar to other Plutonian moons.[15] Hydra's reflectivity is intermediate, in between those of Pluto and Charon.[16] The New Horizons spacecraft imaged Pluto and its moons in July 2015 and returned multiple images of Hydra.[17]