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{{Planet
|image=Nereid.jpg
|caption=Image of Nereid taken by [[Voyager 2]]
|date=May 1, 1949<ref name=usgs>"[http://planetarynames.wr.usgs.gov/append7.html Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers]." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed May 9, 2008.</ref>
|discname=Gerard P. Kuiper<ref name=usgs/><ref name=Kuiper>Kuiper, Gerard P. "[http://articles.adsabs.harvard.edu//full/1949PASP...61..175K/0000175.000.html The Second Satellite of Neptune]." ''Publications of the Astronomical Society of the Pacific'', 61:175-176, 1949. Accessed June 8, 2008.</ref>
|origname=Any of fifty women, daughters of Nereus and Doris, who attended Neptune
|primary=Neptune
|order=8
|periapsis=1,371,734 km<ref name=calc>Calculated</ref>
|apoapsis=9,655,066 km<ref name=calc/>
|semimajor=5,513,400 km<ref name=neptunesatfact>[http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptuniansatfact.html Neptunian Satellite Fact Sheet], [[National Aeronautics and Space Administration|NASA]], January 22, 2008. Accessed May 9, 2008.</ref>
|eccentricity=0.7512<ref name=neptunesatfact/>
|sidereal=360.13619 da<ref name=neptunesatfact/>
|orbitspeed=1.12 km/s<ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/french/nereid.htm Entry for Nereid]." ''Views of the Solar System'', 2000. Accessed June 8, 2008.</ref>
|inclination=27.6°<ref name=Hamilton/>
|siderealday=11.52 hr<ref name=Grav>Grav, Tommy, Holman, Matthew J., and Kavelaars, J. J. "[http://www.journals.uchicago.edu/doi/abs/10.1086/377067 The Short Rotation Period of Neptune]." ''Astrophysical Journal Letters'' 591:L71-L74, July 1, 2003. {{arXiv|astro-ph/0306001|pdf}} {{doi|10.1086/377067}} Accessed June 8, 2008.</ref>
|rotatespeed=0.02576 km/s<ref name=calc/>
|mass=3.09 * 10<sup>19</sup> kg<ref name=calc/>
|density=1,500 kg/m³<ref name=ssdphys>"[http://ssd.jpl.nasa.gov/?sat_phys_par Planetary Satellite Physical Parameters]." [[Jet Propulsion Laboratory|JPL]], [[National Aeronautics and Space Administration|NASA]]. Retrieved June 8, 2008.</ref>
|meanradius=170 km<ref name=ssdphys/>
|surfacegrav=0.713 m/s²<ref name=calc/>
|escapespeed=0.156 km/s<ref name=calc/>
|surfacearea=363,158 km²<ref name=calc/>
|composition=Ice and silicates<ref name=Britannica>"[http://www.britannica.com/eb/article-9055312 Nereid]." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 8 June 2008.</ref>
|color=Neutral gray
|albedo=0.155<ref name=ssdphys/>
}}'''Nereid''', or '''Neptune II''', is the second [[moon]] of [[Neptune]] to be discovered. It is also the third most massive of Neptune's thirteen moons, and eighth in orbit around Neptune.
== Discovery and naming ==
Gerard P. Kuiper discovered Nereid in 1949. He gave it the generic name of the fifty female attendants of Neptune, the [[Rome|Roman]] god of the sea.
== Orbital characteristics ==
Nereid is in a highly eccentric orbit around Neptune, and in fact its orbit is the most eccentric orbit of any [[solar system]] body.<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/nereid.html Entry for Nereid]." ''The <s>Nine</s> 8 Planets'', May 6, 1995. Accessed June 8, 2008.</ref> Its sidereal month is about 360.14 Julian days.
== Rotational characteristics ==
Nereid's sidereal day is 11.52 hours and is considered regular.<ref name=Grav/>
== Physical characteristics ==
Nereid has a mass of 3.09 * 10<sup>19</sup> kg, the third greatest mass of the moons of Neptune. Its color is neutral-gray. Another moon of Neptune, [[Hallimede]] (formerly S/2002 N 1), has the same neutral color, leading some astronomers to suggest that Hallimede is a fragment of Nereid broken off in a collision with another, unknown object.<ref name=Grav2>Grav, T., Holman M. J., and Fraser W. "[http://arxiv.org/abs/astro-ph/0405605 Photometry of Irregular Satellites of Uranus and Neptune]." ''Astrophys. J.'' 613(2004):L77-L80. {{arXiv|astro-ph/0405605v1}} Accessed June 8, 2008.</ref>
== Problems for uniformitarian theories posed by this body ==
Nereid moves in a highly eccentric orbit that is severely inclined to Neptune's equator, though somewhat less inclined to the local Laplace plane. Almost no astronomer believes that Nereid formed with the planet, and most astronomers believe that Neptune is a captured [[Kuiper belt]] or other [[Trans-Neptunian objects|trans-Neptunian object]].
== Observation and Exploration ==
Telescopic observation has revealed little about Nereid beyond its orbital elements. The one spacecraft that visited the Neptunian system, [[Voyager 2]], captured one low-resolution image of Nereid but did not fly close enough to it to discover more.
== References ==
{{reflist|2}}
{{Solarsystem}}
{{Solarsystem}}
[[Category:Astronomy]]
[[category:astronomy]]