Nix (moon)
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{| class="toccolours" style="margin-left: 1em; float: right; border: 1px solid #CCC;"
|+ '''<big>Nix</big>'''
|-
| bgcolor="#000000" colspan="2" align="center"| [[Image:Plutonian system.jpg|275px]]<br /> <font color="white"><small>Artist conception of Hydra (foreground),<br />Pluto and Charon (background),<br />and Nix (bright dot center left)</small></font>
|-
! bgcolor="#a0ffa0" colspan="2" | Discovery
|-
! align="left" valign=top | Discovered by
| [[Hubble Space Telescope]]<br>Pluto Companion Search Team
|-
! align="left" | Discovered in
| June 2005
|-
! bgcolor="#a0ffa0" colspan="2" | Nictian [[orbit]]al characteristics<ref name="Buie06">{{cite journal |author=Buie, M. W. |coauthors=[[William M. Grundy|Grundy, W. M.]]; Young, E. F.; Young, L. A.; and Stern, S. A. |title=''Orbits and Photometry of Pluto's satellites: Charon, S/2005 P1, and S/2005 P2'' [sic] |journal= Astronomical Journal |year=2006 |volume=132 |pages=290 |doi=10.1086/504422 }}([http://arxiv.org/abs/astro-ph/0512491v2 Final preprint])</ref>
|-
! align="left" | [[Semi-major axis]]<sup>a</sup>
| 48 675 ± 120 km
|-
! align="left" | [[Eccentricity (orbit)|Eccentricity]]
| 0.002 ± 0.002
|-
! align="left" | [[Orbital period]]
| 24.856 ± 0.001 d
|-
! align="left" | [[Inclination]]<sup>b</sup>
| 0.04° ± 0.22°
|-
! align="left" | Parent body
| [[Pluto]]
|-
! bgcolor="#a0ffa0" colspan="2" | Physical characteristics
|-
! align="left" | Mean [[diameter]]
| 46 − 137 km<ref name="Weaver2006">
{{cite journal | author = H. A. Weaver |coauthors = S. A. Stern, M. J. Mutchler, A. J. Steffl, M. W. Buie, W. J. Merline, J. R. Spencer, E. F. Young and L. A. Young | year = 2006 | month = 23 February | title = Discovery of two new satellites of Pluto | journal = Nature | volume = 439| issue = 7079 | pages = 943–945| doi = 10.1038/nature04547 | url = http://arxiv.org/pdf/astro-ph/0601018 | accessdate = 2007-11-11 | format = subscription required}}</ref>
|-
! align="left" | [[Mass]]
| 5×10<sup>16</sup> − 2×10<sup>18</sup> kg<ref> Based on the range of diameters from Buie ''et al.'' (2006), and densities ranging from 1 g/cm³ (ice) to 2 g/cm³ (Pluto).</ref>
|-
! align="left" | Mean [[density]]
| ''unknown''
|-
! align="left" | [[Sideral day|Rotation period]]
| ''unknown''
|-
! align="left" | [[Axial tilt]]
| ''unknown''
|-
| align="left" | '''[[Albedo]]'''
| 0.04 − 0.35 (assumed)<ref name="Stern06b"/>
|-
! align="left" | [[Apparent Magnitude]]
| 23.38 to 23.7 (measured)<ref name="Stern06b"/>
|-
! align="left" | Surface [[Temperature|temp.]]
| 33-55 [[Kelvin|K]]
|-
! align="left" | [[Celestial body atmosphere|Atmosphere]]
| none
|-
|colspan=2|
----
|-
|colspan=2| {{smaller|
<sup>a</sup> Relative to the Pluto-Charon [[barycenter]].<br>
<sup>b</sup> Relative to Pluto's equator (also Charon's orbital plane).<br>
<sup>c</sup> Based on assumed albedo.}}
|}
'''Nix''' ({{pronEng|ˈnɪks}}) is a [[natural satellite]] of [[Pluto]]. It was discovered along with [[Hydra (moon)|Hydra]] in June 2005 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]]; the moons 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 [[precovery|precoveries]] from 2002. The moons were [[provisional designation in astronomy|provisionally designated]] '''S/2005 P 1''' (Hydra) and '''S/2005 P 2''' (Nix).<ref name="IAUC8625">[http://cfa-www.harvard.edu/iau/special/08625.pdf IAU Circular No. 8625] describing the discovery</ref><ref name="IAUC8723"/>
The moon follows a circular orbit in the same plane as [[Charon (moon)|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.<ref name=" Buie06"/> A hypothesis explaining such a near-resonance is that it originated before the outward migration of Charon following the formation of all three known moons, and is maintained by the periodic local fluctuation of 9% in the Pluto-Charon gravitational field strength.<!--- The instantaneous force in the Pluto-Charon-Nix alignment case is 9.46% larger than in the quadrature case (where Nix is 90° from the Pluto-Charon axis); the Charon-Pluto-Nix case is almost exactly halfway between these values. In Buie ''et al.'', the quote is "The gravitational force exerted by Pluto on either P1 or P2 varies by roughly 15% (peak-to-peak)." Pluto's gravitational pull, ''by itself'', varies by 18% for Nix and 13% for Hydra --->
[[Image:Pluto system 2005 discovery images.jpg|thumb|250px|left|Discovery images of ''' Nix and Hydra'''.]]
Although its size has not been directly measured, the moon is calculated to have a diameter of between 46 km, if its [[albedo|reflectivity]] is similar to Charon's 35%, and 137 km, if it has a reflectivity of 4%, like the darkest [[Kuiper Belt Object]]s.<ref name="Weaver2006"/> Nix is slightly fainter than [[Hydra (moon)| Hydra]], suggesting that it is somewhat smaller in size.<ref name="Stern06b"/> In the discovery image, Nix is 6,300 times fainter than Pluto.<ref name=brightness>Brightness Difference on 2005-05-15: (5th root of 100) ^ (Nix [[Apparent Magnitude|APmag]] 23.38 - Pluto APmag 13.87) = 6,368x</ref>
Early research appeared to show that Nix was reddish like [[Pluto]] and unlike the other moons,<ref name="Buie06"/> but more recent reports have been that it is grey like the remaining satellites.<ref name="Stern06b">{{cite journal | author=Stern, S. A. |coauthors=Mutchler, M. J.; Weaver, H. A.; and Steffl, A. J. |title=''The Positions, Colors, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005-2006'' |journal=Astronomical Journal |year=2006 |pages=submitted }} ([http://www.arxiv.org/abs/astro-ph/0605014 Final preprint])</ref>
Nix is to be visited along with Pluto by the ''[[New Horizons]]'' mission in 2015.
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,<ref name="IAUC8723">[http://www-int.stsci.edu/~mutchler/documents/IAU_Circular_8723.pdf IAU Circular No. 8723] naming the moons</ref> where the designation '''Pluto II''' is also given. Together with Hydra, Pluto's third moon, the initials are those of the ''[[New Horizons]]'' probe. The initial proposal was to use the [[Classical Greek|Classical]] spelling [[Nyx (mythology)|Nyx]], but to avoid confusion with the [[asteroid]] [[3908 Nyx]], this was changed to "the Egyptian<!--Coptic--> spelling of the Greek name".<ref name="Gazetteer">{{cite web
| title=Planet and Satellite Names and Discoverers
| work=Gazetteer of Planetary Nomenclature
| publisher=USGS Astrogeology
| date=July 21, 2006
| url=http://planetarynames.wr.usgs.gov/append7.html
| accessdate=2006-08-15 }}</ref>
==References==
{{reflist}}
<div class="references-small">
#<li value="9"> {{cite journal|journal=The Astronomical Journal |author=Steffl, A. J. |coauthors=Mutchler, M. J.; Weaver, H. A.; Stern, S. A.; [[Daniel David Durda|Durda, D. D.]]; [[Dirk Terrell|Terrell, D.]]; Merline, W. J.; Young, L. A.; Young, E. F.; Buie, M. W.; and Spencer, J. R. |year=2006 |title=New Constraints on Additional Satellites of the Pluto System |volume=132 |pages=614–619 |doi=10.1086/505424 }}([http://arxiv.org/abs/astro-ph/0511837 Final preprint])
</div>
==External links==
* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Plu_Nix Nix Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://www.boulder.swri.edu/plutonews/ Background Information Regarding Our Two Newly Discovered Satellites of Pluto] – The discoverers' website
* [http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/19/ NASA's Hubble Reveals Possible New Moons Around Pluto] – Hubble press release
* [http://www.space.com/scienceastronomy/051031_pluto_moons.html Two More Moons Discovered Orbiting Pluto] (SPACE.com)
* [http://www.space.com/scienceastronomy/060621_nix_hydra.html Pluto's Newest Moons Named Hydra and Nix] (SPACE.com)
{{Moons of dwarf planets}}
{{Trans-Neptunian objects}}
[[Category:Pluto's moons]]
[[als:Nix (Mond)]]
[[ar:نيكس]]
[[be-x-old:Нікс (спадарожнік)]]
[[br:Nix]]
[[bg:Никта (спътник)]]
[[ca:Nix (satèl·lit)]]
[[cs:Nix (měsíc)]]
[[cy:Nix (lloeren)]]
[[da:Nix]]
[[de:Nix (Mond)]]
[[es:Nix (luna)]]
[[eo:Nikso (astronomio)]]
[[fr:Nix (lune)]]
[[ga:Nix]]
[[gv:Nix (fo-phlannad)]]
[[ko:닉스 (위성)]]
[[hr:Nikta (mjesec)]]
[[io:S/2005 P 2]]
[[it:Notte (astronomia)]]
[[lt:Niktė (palydovas)]]
[[hu:Nix (hold)]]
[[nl:Nix (maan)]]
[[ja:ニクス (衛星)]]
[[no:Nix (måne)]]
[[nn:Nix]]
[[nds:Nix (Maand)]]
[[pl:Nix (księżyc)]]
[[pt:Nix (satélite)]]
[[ru:Никта (спутник)]]
[[simple:Nix (moon)]]
[[sk:Nix (mesiac)]]
[[sl:Niks (luna)]]
[[fi:Nix]]
[[sv:Nix (måne)]]
[[zh:冥卫二]]