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Space Topics: Neptune

Neptune's Moons

Neptune has far fewer moons (13 are now known) than all the other outer planets, and only one of them, Triton, is large enough to be a world unto itself.  Unlike all other large icy satellites, Triton is in a retrograde orbit (that is, it orbits opposite to the planet’s sense of rotation), which could mean that Triton was a wayward object that formed elsewhere and was captured into Neptune orbit.  Only Triton and Nereid were known prior to the Voyager 2 encounter.  Voyager 2 yielded six more moons in circular orbits close to the planet and its rings.  Another five likely captured moons have been discovered in telescopic surveys since 2002.  Nereid has the most elliptical orbit of any moon in the solar system, zooming in to 1 million and out to 9 million kilometers (0.6 to 5.6 million miles) from Neptune.

Naiad
58 kilometers diameter; 48,200 kilometers from Neptune

Thalassa
80 kilometers diameter; 50,100 kilometers from Neptune

Despina
148 kilometers diameter; 52,500 kilometers from Neptune

Galatea
158 kilometers diameter; 62,000 kilometers from Neptune

Larissa at a scale of 20 km/pixel

Larissa
192 kilometers diameter; 73,500 kilometers from Neptune

Proteus at a scale of 20 km/pixel

Proteus
416 kilometers diameter; 117,600 kilometers from Neptune

Triton at a scale of 20 km/pixel

Triton
2706 kilometers diameter; 354,800 kilometers from Neptune

Nereid
340 kilometers diameter; 5,513,400 kilometers from Neptune

Halimede (S/2002 N1)
61 kilometers diameter; 15,728,000 kilometers from Neptune

Sao (S/2002 N2)
40 kilometers diameter; 22,422,190 kilometers from Neptune

Laomedeia (S/2002 N3)
40 kilometers diameter; 23,571,200 kilometers from Neptune

Psamathe (S/2003 N1)
38 kilometers diameter; 46,695,000 kilometers from Neptune

Neso (S/2002 N4)
60 kilometers diameter; 48,838,670 kilometers from Neptune

Check these sites for the most up-to-date facts on Neptune's small satellites.
Scott Sheppard's Neptune Satellite Page
NASA's Solar System Dynamics pages: Satellite Properties and Satellite Elements