This is an old revision of this page, as edited by JorisvS (talk | contribs) at 08:03, 28 May 2015 (Undid revision 664341417 by Exoplanetaryscience) with such a low eccentricity, I sincerely doubt this has anything to do with perihelion and aphelion but just our viewing angle). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
Revision as of 08:03, 28 May 2015 by JorisvS (talk | contribs) (Undid revision 664341417 by Exoplanetaryscience) with such a low eccentricity, I sincerely doubt this has anything to do with perihelion and aphelion but just our viewing angle)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff) Discovery images of Hydra (and Nix) | |
| Discovery | |
|---|---|
| Discovered by | Hubble Space Telescope Pluto Companion Search Team |
| Discovery date | June 2005 |
| Designations | |
| Pronunciation | /ˈhaɪdrə/ |
| Named after | Lernaean Hydra |
| Alternative names | (134340) Pluto III |
| Adjectives | Hydrian |
| Orbital characteristics | |
| Semi-major axis | 64749 km |
| Eccentricity | 0.0051 |
| Orbital period (sidereal) | 38.206±0.001 d |
| Inclination | 0.212° |
| Satellite of | Pluto |
| Physical characteristics | |
| Mean radius | 30–84 km |
| Mass | 4.2×10 kg |
| Mean density | (unknown) |
| Synodic rotation period | (unknown) |
| Axial tilt | (unknown) |
| Albedo | 0.04–0.35 (assumed) |
| Temperature | 33–55 K |
| Apparent magnitude | 22.9–23.3 (measured) |
Hydra is the outermost known natural satellite of Pluto. It was discovered along with Nix in June 2005, and is to be visited along with Pluto by the New Horizons mission in July 2015.
Discovery
Hydra was discovered by the Hubble Space Telescope's "Pluto Companion Search Team", consisting of Hal A. Weaver, Alan Stern, Max J. Mutchler, Andrew J. Steffl, Marc W. Buie, William J. Merline, John R. Spencer, Eliot F. Young, and Leslie A. Young. The discovery images were taken on May 15, 2005, and May 18, 2005; Nix and Hydra were independently discovered by Max J. Mutchler on June 15, 2005, and Andrew J. Steffl on August 15, 2005. The discoveries were announced on October 31, 2005, after confirmation by precoveries from 2002. They were provisionally designated S/2005 P 1 (Hydra) and S/2005 P 2 (Nix).
Name
The name Hydra was announced on June 21, 2006, in IAU Circular 8723, along with the formal designation Pluto III. The name is that of the Hydra, the nine-headed serpent which battled Hercules in Greek mythology. The nine heads of Hydra are a reference to Pluto's tenure as the ninth planet; its initial, H, refers to the Hubble Telescope, which discovered Hydra and, together with Nix, to the New Horizons mission whose safe passage was the motivation for taking the Hubble images.
Orbital properties
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The satellite orbits the barycenter of the system in the same plane as Charon and Nix, at a distance of about 65,000 km. Unlike other satellites of Pluto, its orbit is only nearly circular; its eccentricity of 0.0052 is small, but significantly non-zero. Its orbital period of 38.2 days is close to a 1:6 orbital resonance with Charon, with the timing discrepancy being 0.3%. Whether this is an actual resonance awaits more detailed determinations of its orbit, in particular its rate of precession. If there is no actual resonance, a hypothesis to explain the near-resonance is that it originated before the outward migration of Charon following the formation of all five known moons, and is maintained by the periodic local fluctuation of 5% in the Pluto–Charon gravitational field strength.
Physical properties
Although its size has not been directly measured, calculations based on its brightness give it a diameter of between 61 and 167 kilometers (38 and 104 mi). To meet the lower end of the range, its geometric albedo would have to be similar to Charon's 35%. For it to be the at the higher end of the range, it would have to have a reflectivity of 4%, like the darkest Kuiper belt objects. At the time of discovery, Hydra was about 25 percent brighter than its sister moon Nix, which led to the assumption that its diameter was some 10 percent larger. Pre-discovery data from Hubble observations in 2002–03 implied that Nix was the brighter moon. However, Hubble observations in 2005–06, specifically targeting the dim moons, once again showed Hydra to be a little brighter. Hydra appears to be spectrally neutral like Charon and Nix, whereas Pluto is reddish.
References
- ^
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|doi= 10.1086/504422instead.. a, i, e per JPL (site updated 2008 Aug 25) - ^
H. A. Weaver; S. A. Stern; M. J. Mutchler; A. J. Steffl; M. W. Buie; W. J. Merline; J. R. Spencer; E. F. Young; L. A. Young (23 February 2006). "Discovery of two new satellites of Pluto". Nature. 439 (7079): 943–945. arXiv:astro-ph/0601018. Bibcode:2006Natur.439..943W. doi:10.1038/nature04547. PMID 16495991.
{{cite journal}}: Unknown parameter|lastauthoramp=ignored (|name-list-style=suggested) (help) - Tholen, David J.; M. W. Buie; W. M. Grundy (October 2010). "Improved Masses of Nix and Hydra". AAS DPS Meeting #42. 42: 984. Bibcode:2010DPS....42.2008T.
- ^ 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): submitted. arXiv:astro-ph/0607507. Bibcode:2006AJ....132.1405S. doi:10.1086/506347. (Final preprint)
- Cain, Fraser (2008). "Pluto's Moon Hydra".
- IAU Circular No. 8625 describing the discovery
- ^ IAU Circular No. 8723 naming the moons
- Neil deGrasse Tyson, 2009, The Pluto Files
- Stern, Alan; Hal Weaver (JHU APL); Max Mutchler (STScI); Andrew Steffl (SwRI); Bill Merline (SwRI); Marc Buie (Lowell Observatory); John Spencer (SwRI); Eliot Young (SwRI); Leslie Young (SwRI) (15 May 2005). "Background Information Regarding Our Two Newly Discovered Satellites of Pluto". Planetary Science Directorate (Boulder Office). Retrieved 2007-11-10.
{{cite web}}: Unknown parameter|lastauthoramp=ignored (|name-list-style=suggested) (help)
- Steffl, A. J.; Mutchler, M. J.; Weaver, H. A.; Stern, S. A.; Durda, D. D.; Terrell, D.; Merline, W. J.; Young, L. A.; Young, E. F.; Buie, M. W.; Spencer, J. R. (2006). "New Constraints on Additional Satellites of the Pluto System". The Astronomical Journal. 132 (2): 614–619. arXiv:astro-ph/0511837. Bibcode:2006AJ....132..614S. doi:10.1086/505424.
{{cite journal}}: Unknown parameter|lastauthoramp=ignored (|name-list-style=suggested) (help)(Final preprint)
External links
- Hydra Profile by NASA's Solar System Exploration
- NASA's Hubble Reveals Possible New Moons Around Pluto – Hubble press release
- Two More Moons Discovered Orbiting Pluto (SPACE.com)
- Pluto's Newest Moons Named Hydra and Nix (SPACE.com)
- Hydra at ESA/Hubble
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