Nereid (moon)

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Nereid

Discovery
Discovered by:	Gerard P. Kuiper[1]
Discovery date:	May 1, 1949
Orbital characteristics
Periapsis:	1,353,600 km (0.00905 AU)
Apoapsis:	9,623,700 km (0.06433 AU)
Semi-major axis:	5,513,400 km (0.03685 AU)
Eccentricity:	0.7512
Orbital period:	360.1362 d
Avg. orbital speed:	1.12 km/s
Max. orbital speed:	2.95 km/s
Min. orbital speed:	0.42 km/s
Inclination:	5.07° (to Ecliptic) 32.55° (to Neptune's equator) 7.232° (to the local Laplace plane)
Satellite of:	Neptune
Physical characteristics
Mean radius:	170 km
Mass:	3.1×1019 kg[citation needed]
Mean density:	1.5 g/cm3
Rotation period:	0.48 d (11 h 31 min)[2]
Albedo:	0.14
Temperature:	~51 K mean (estimate)

Nereid (IPA: [ˈnɪ.ɹi.ɪd], IPA: [ˈnɛ.ɹi.ɪd], Greek Νηρηίδα), or Neptune II, is a moon of Neptune.

Nereid was discovered on 1 May 1949 by Gerard P. Kuiper. It is named after the Nereids, sea-nymphs of Greek mythology.

It was the outermost of Neptune's known moons for a long time (Halimede through Neso have since taken that honour), and is the third largest, with a diameter of 340 km. Its orbit averages 5,513,400 km in radius, but is highly eccentric and varies from 1,353,600 to 9,623,700 kilometres. This is the most highly eccentric orbit of any known satellite in the solar system. The unusual orbit suggests that it may be a captured asteroid or Kuiper belt object, or possibly that it was perturbed during the capture of Neptune's largest moon Triton. Very little else is known of Nereid.

Nereid was too far to be properly imaged by the Voyager 2 probe when it visited the Neptune system in 1989. Photos sent back show only its highly irregular shape as no surface features could be seen at the resolution available.

A simulated view of Nereid with Neptune in the distance. The surface details are fictional.

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