Hydra (moon)

Hydra
Near true-color image of Hydra, taken by New Horizons on 14 July 2015
Discovery[1]
Discovered byHubble Space Telescope
Discovery date15 May 2005
Designations
Designation
Pluto III[1]
Pronunciation/ˈhaɪdrə/[2]
Named after
Lernaean Hydra
Alternative names
S/2005 P 1
AdjectivesHydrian[3] /ˈhaɪdriən/[4]
Orbital characteristics[5]
64738±3 km
Eccentricity0.005862±0.000025
38.20177±0.00003 d
Average orbital speed
0.123 km/s
Inclination0.242°±0.005°
Satellite ofPluto
Physical characteristics
Dimensions50.9 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 
Surface gravity
0.00520055269 g[8]
Synodic rotation period
0.4295 d (10.31 h)[9] (July 2015)
110°[10]
Albedo0.83 ± 0.08 (geometric)[11]
Temperature23 K[12]
22.9–23.3 (measured)[13]

Hydra, formal designation (134340) Pluto III, 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]

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]

  1. ^ a b c "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN). Retrieved 17 May 2021.
  2. ^ "hydra". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  3. ^ Davenport (1843) A new geographical, historical, and commercial grammar
  4. ^ per "hydria". Lexico UK English Dictionary. Oxford University Press. Archived from the original on March 22, 2020.
  5. ^ Showalter, M. R.; Hamilton, D. P. (3 June 2015). "Resonant interactions and chaotic rotation of Pluto's small moons". Nature. 522 (7554): 45–49. Bibcode:2015Natur.522...45S. doi:10.1038/nature14469. PMID 26040889. S2CID 205243819.
  6. ^ a b Verbiscer, A. J.; Porter, S. B.; Buratti, B. J.; Weaver, H. A.; Spencer, J. R.; Showalter, M. R.; Buie, M. W.; Hofgartner, J. D.; Hicks, M. D.; Ennico-Smith, K.; Olkin, C. B.; Stern, S. A.; Young, L. A.; Cheng, A. (2018). "Phase Curves of Nix and Hydra from the New Horizons Imaging Cameras". The Astrophysical Journal. 852 (2): L35. Bibcode:2018ApJ...852L..35V. doi:10.3847/2041-8213/aaa486.
  7. ^ a b Cite error: The named reference Porter2023 was invoked but never defined (see the help page).
  8. ^ "Hydra By the Numbers". solarsystem.nasa.gov. NASA. 21 November 2017. Retrieved 7 March 2019.
    (Original value of 0.051 m/s2 converted to g)
  9. ^ Cite error: The named reference Lakdawalla2015 was invoked but never defined (see the help page).
  10. ^ Weaver, H. A.; Buie, M. W.; Showalter, M. R.; Stern, S. A.; et al. (18 April 2016). "The Small Satellites of Pluto as Observed by New Horizons". Science. 351 (6279) aae0030. arXiv:1604.05366. Bibcode:2016Sci...351.0030W. doi:10.1126/science.aae0030. PMID 26989256. S2CID 206646188.
  11. ^ a b Stern, S. A.; Bagenal, F.; Ennico, K.; Gladstone, G. R.; et al. (15 October 2015). "The Pluto system: Initial results from its exploration by New Horizons". Science. 350 (6258) aad1815. arXiv:1510.07704. Bibcode:2015Sci...350.1815S. doi:10.1126/science.aad1815. PMID 26472913. S2CID 1220226.
  12. ^ Cook, Jason C.; Dalle Ore, Cristina M.; Protopapa, Silvia; Binzel, Richard P.; Cartwright, Richard; Cruikshank, Dale P.; et al. (15 November 2018). "Composition of Pluto's small satellites: Analysis of New Horizons spectral images". Icarus. 315 (1964): 30–45. Bibcode:2017LPI....48.2478C. doi:10.1016/j.icarus.2018.05.024. S2CID 125374498.
  13. ^ Stern, S. A.; Mutchler, M. J.; Weaver, H. A.; Steffl, A. J. (2006). "The Positions, Colors, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005–2006". Astronomical Journal. 132 (3): 1405–1414. arXiv:astro-ph/0607507. Bibcode:2006AJ....132.1405S. doi:10.1086/506347. S2CID 14360964. (Final preprint)
  14. ^ Stern, Alan; Grinspoon, David (May 1, 2018). "Chapter 7: Bringing It All Together". Chasing New Horizons: Inside the Epic First Mission to Pluto. Picador. ISBN 978-1-250-09896-2.
  15. ^ Keeter, Bill (5 May 2016). "Pluto's Icy Moon Hydra". NASA. Archived from the original on 22 January 2018. Retrieved 20 February 2018.
  16. ^ NASA (15 July 2015). "Hydra Emerges from the Shadows". Retrieved 16 July 2015.
  17. ^ "New Horizons 'Captures' Two of Pluto's Smaller Moons". Johns Hopkins University Applied Physics Laboratory. 21 July 2015. Retrieved 22 July 2015.
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