Hydra (moon): Difference between revisions
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==Exploration== |
==Exploration== |
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[[File:Hydra (moon) 2015-7-15 (raw).jpg|thumb|275px|Raw, pixelated image of Hydra]] |
[[File:Hydra (moon) 2015-7-15 (raw).jpg|thumb|275px|Raw, pixelated image of Hydra]] |
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The only close-up and detailed photographs of Hydra were taken by the ''[[New Horizons]]'' spacecraft from approximately 400,000 miles away during |
The only close-up and detailed photographs of Hydra were taken by the ''[[New Horizons]]'' spacecraft from approximately 400,000 miles away during its historic flyby of the '''Pluto-Charon''' system on July 14, 2015-Tuesday. The spacecraft also studied the surface composition, [[reflectivity]] and other basic physical properties of Hydra. |
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== References == |
== References == |
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Revision as of 11:02, 16 July 2015
_2015-7-15_(processed).png) Processed photograph of Hydra taken by New Horizons on 14 July 2015 | |
| Discovery | |
|---|---|
| Discovered by | Hubble Space Telescope Pluto Companion Search Team |
| Discovery date | June 2005 |
| Designations | |
| Pronunciation | /ˈhaɪdrə/ |
Named after | Lernaean Hydra |
| (134340) Pluto III | |
| Adjectives | Hydrian |
| Orbital characteristics[1] | |
| 64738±3 km | |
| Eccentricity | 0.005862±0.000025 |
| 38.20177±0.00003 d | |
| Inclination | 0.242°±0.005° |
| Satellite of | Pluto |
| Physical characteristics | |
| Dimensions | 43 × 33 km ± ?[2] |
| Mass | 4.2×1017 kg[3][dubious – discuss] |
| chaotic | |
| variable | |
| Albedo | 0.20-0.45 |
| Temperature | 33–55 K |
| 22.9–23.3 (measured)[4] | |
Hydra is the outermost known natural satellite of Pluto. It was discovered along with Nix in June 2005, and was visited along with Pluto by New Horizons in July 2015. Hydra's surface is probably covered with water ice, the most abundant ice in the universe. Observed within Hydra's bright regions is a darker circular structure with a diameter of approximately 6 miles (10 kilometers). Hydra's reflectivity (the percentage of incident light reflected from the surface) is intermediate between that of Pluto and Charon.[5][6] Images should have resolutions as high as 780 m/px.
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).[7][8]
Name
The name Hydra was announced on June 21, 2006, in IAU Circular 8723,[8] 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.[9]
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. Its eccentricity of 0.0059 is small, but significantly non-zero, and the largest of those of Pluto's small moons (slightly greater than that of Styx).
Hydra is in a 2:3 orbital resonance with Nix, and a 6:11 resonance with Styx (the ratios represent numbers of orbits completed per unit time; the period ratios are the inverses).[10][1] As a result of this "Laplace-like" 3-body resonance, it has conjunctions with Styx and Nix in a 5:3 ratio.
Its orbital period of 38.2 days is also close to a 1:6 orbital resonance with Charon, with the timing discrepancy being 0.3%. 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.
Hydra's rotation is chaotic. The body tumbles like Nix and Saturn's moon Hyperion.
Physical properties
Hydra is irregular in shape, 43 × 33 km in cross-section from one side. It is spectrally neutral like Charon and Nix (whereas Pluto is reddish) and is composed primarily of water ice,[11] probably ice XI.
Exploration
_2015-7-15_(raw).jpg)
The only close-up and detailed photographs of Hydra were taken by the New Horizons spacecraft from approximately 400,000 miles away during its historic flyby of the Pluto-Charon system on July 14, 2015-Tuesday. The spacecraft also studied the surface composition, reflectivity and other basic physical properties of Hydra.
References
- ^ a b Showalter, M. R.; Hamilton, D. P. (3 June 2015). "Resonant interactions and chaotic rotation of Pluto's small moons". Nature. 522 (7554): 45–49. doi:10.1038/nature14469.
- ^ [1]
- ^ 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)
- ^ https://www.nasa.gov/image-feature/hydra-emerges-from-the-shadows
- ^ NASA/APL (2008). "Pluto's Moon Hydra".
- ^ IAU Circular No. 8625 describing the discovery
- ^ a b IAU Circular No. 8723 naming the moons
- ^ Neil deGrasse Tyson, 2009, The Pluto Files
- ^ Witze, Alexandra (2015). "Pluto's moons move in synchrony". Nature. doi:10.1038/nature.2015.17681.
- ^ https://twitter.com/NASANewHorizons/status/621396353852248064
- 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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