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Nix

Discovery images of Nix (and Hydra)
Discovery
Discovered by	Hubble Space Telescope Pluto Companion Search Team
Discovery date	June 2005
Designations
Pronunciation	/ˈnɪks/
Named after	Nyx
Alternative names	(134340) Pluto II
Adjectives	Nictian
Orbital characteristics
Semi-major axis	48708 km
Eccentricity	0.0030
Orbital period (sidereal)	24.856±0.001 d
Inclination	0.195°
Satellite of	Pluto
Physical characteristics
Mean radius	23–68 km
Mass	5×10 to 2×10 kg
Mean density	(unknown)
Synodic rotation period	Chaotic
Axial tilt	(unknown)
Albedo	0.04–0.35 (assumed)
Temperature	33–55 K
Apparent magnitude	23.38–23.7 (measured)

Nix is a natural satellite of Pluto. It was discovered along with Hydra in June 2005, and is to be imaged along with Pluto and Charon by the New Horizons mission in July 2015. Of the four small Plutonian moons, New Horizons is expected to get the best pictures of Nix.

Discovery

Nix was found by the Hubble Space Telescope Pluto Companion Search Team, composed of Hal A. Weaver, S. 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).

Orbit

Nix follows a circular orbit in the same plane as Charon. Its orbital period of 24.9 days is close to a 1:4 orbital resonance with Charon, but the timing discrepancy is 2.7%, which suggests that there is no active resonance. A hypothesis explaining such a 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 9% in the Pluto–Charon gravitational field strength.

As it orbits, it flips up and down on its axis, with the north pole becoming the south pole and vice versa, periodically.

Physical characteristics

Although its size has not been directly measured, Nix has been calculated to have a diameter of between 46 and 137 kilometers (29 and 85 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. Nix is slightly fainter than Hydra, suggesting that it is somewhat smaller in size. In the discovery image, Nix is 6,300 times fainter than Pluto.

Early research appeared to show that Nix was reddish like Pluto and unlike the other moons, but more recent reports have been that it is grey like the remaining satellites.

Name

The formal name "Nix", from the Greek goddess of darkness and night and mother of Charon, was announced on June 21, 2006 on IAU Circular 8723, where the designation Pluto II is also given. Together with Hydra (Pluto's third moon) the initials are those of the unmanned New Horizons spaceprobe. The initial proposal was to use the classical spelling Nyx, but to avoid confusion with the asteroid 3908 Nyx the spelling was changed to Nix. The USGS Gazetteer of Planetary Nomenclature states that Nix is the "Egyptian spelling", while Jürgen Blunck explains it as the "Spanish translation" of the Greek name.

See also

• Moons of Pluto

References

1. Jennifer Blue (2009-11-09). "Gazetteer of Planetary Nomenclature". IAU Working Group for Planetary System Nomenclature (WGPSN). Retrieved 2010-08-30.
2. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1086/504422 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1086/504422 instead.. a, i, e per JPL (site updated 2008 Aug 25)
3. ^ H. A. Weaver; S. A. Stern; M. J. Mutchler; A. J. Steffl; et al. (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 |last-author-amp= ignored (|name-list-style= suggested) (help)
4. Based on the range of diameters from Buie et al. (2006), and densities ranging from 1 g/cm (ice) to 2 g/cm (Pluto).
5. http://www.nasa.gov/press-release/nasa-s-hubble-finds-pluto-s-moons-tumbling-in-absolute-chaos
6. ^ 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)
7. Cain, Fraser (2008). "Pluto's Moon Nix".
8. IAU Circular No. 8625 describing the discovery
9. ^ IAU Circular No. 8723 naming the moons
10. Boyle, Alan. "Pluto's Moons Raise New Puzzles for NASA's New Horizons Mission". NBC News.com. NBC News. Retrieved 3 June 2015.
11. Brightness Difference on 2005-05-15: (5th root of 100) ^ (Nix APmag 23.38 – Pluto APmag 13.87) = 6,368x
12. "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology. July 21, 2006. Retrieved 2006-08-15.
13. Blunck, Jürgen, Solar System Moons: Discovery and Mythology (2009), p. 129.

• Steffl, A. J.; Mutchler, M. J.; Weaver, H. A.; Stern, S. A.; et al. (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 |last-author-amp= ignored (|name-list-style= suggested) (help)(Final preprint)

External links

• Nix Profile by NASA's Solar System Exploration
• Background Information Regarding Our Two Newly Discovered Satellites of Pluto – The discoverers' website
• 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)

v t e Pluto
Atmosphere Climate Geology
Geography (features)	Regions "Brass Knuckles" Safronov Sharaf Harrington Vucub-Came Hun-Came Meng-pʻo Belton Cadejo Hayabusa Lowell Morgoth Pioneer Tombaugh "The Heart" Venera Viking Voyager Hills and mountains Baret Montes Challenger Colles Coleta de Dados Colles Hillary Montes Piccard Mons Tenzing Montes Wright Mons Plains Sputnik Planitia Valleys and depressions Adlivun Cavus Lineae Luna Linea Craters Burney
Moons	Charon Hydra Kerberos Nix Styx
Exploration	New Horizons
Astronomy	Official definitions Definition of planet IAU definition of planet Scientist opinions Alan Stern Michael E. Brown Neil deGrasse Tyson Discovery Planet X Lowell Observatory Percival Lowell Clyde Tombaugh Roger Putnam General Double planet Dwarf planet Planet Plutino Trans-Neptunian object Kuiper belt
Related	Fiction Mythology Venetia Burney

• Moons of Pluto
• Astronomical objects discovered in 2005