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Neptune Menu  

Neptune's Moons

Neptune has at least 14 moons known to orbit it. Its largest moon is Triton which was discovered in 1846 by the English beer brewer and astronomer William Lassell. It was discovered only 17 days after Neptune itself was first observed. Triton is the only major moon of a planet to orbit in the opposite direction of the planet's rotation. This retrograde orbit suggests that Triton might not have originally formed around Neptune as most large moons do, but was captured by it instead.

Crescents of Neptune and Triton from Voyager 2 in 1989 (Image credit: NASA/JPL)

Voyager 2 is a spacecraft that visited Neptune in 1989. Prior to its arrival, the only moon other than Triton to be discovered in orbit of Neptune was Nereid by the Dutch astronomer Gerard Kuiper in 1949. Voyager 2 would find most of Neptune's known inner moons. Astronomers have since discovered a handful of other moons orbiting Neptune. These are mostly outer moons orbiting at great distances away from Neptune. Its most distant moon is Neso which is over 48 million kilometres (30 million miles) away from Neptune itself, making it the most distant moon of any planet in the solar system.

Neptune's moons can be split into four distinct groups as listed below. Following that is a list of the moons themselves.


Groups of Neptune's Moons

Inner Moons
The closest moons to Neptune which orbit in the same direction of Neptune's rotation and on a similar plane to the planet's equator.
Major Moon
Just Triton! This is a large moon which orbits in an opposite direction to the planet's rotation.
Irregular Retrograde
Outer moons situated between 5 million to 24 million kilometres (3 million to 15 million miles) from Neptune with orbits that vary in shape (some are circular, others are more oval-shaped) and inclined between 7 and 49 degrees. They travel in an opposite direction to Neptune's rotation.
Irregular Prograde
Outer moons situated between 15 million to 49 million kilometres (9 million to 30 million miles) from Neptune with orbits that vary in shape and inclined between 7 and 49 degrees. They travel in the same direction as Neptune's rotation.

List of Neptune's Moons

Name of Moon Diameter Orbital Distance Length of Orbit Discovered Discoverer Group
Naiad 60 km (96 x 60 x 52 km)
38 miles
48,277 km
29,998 miles
7 hours 1989 Voyager Imaging Team Inner
Thalassa 81 km (108 x 100 x 52 km)
51 miles
50,075 km
31,115 miles
7.5 hours 1989 Voyager Imaging Team Inner
Despina 156 km (180 x 148 x 128 km)
97 miles
52,526 km
32,638 miles
8 hours 1989 Voyager Imaging Team Inner
Galatea 175 km (204 x 184 x 144 km)
109 miles
61,653 km
38,309 miles
10 hours 1989 Voyager Imaging Team Inner
Larissa 194 km (216 x 204 x 168 km)
121 miles
73,548 km
45,701 miles
13 hours 1981 Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky, David J. Tholen Inner
Hippocamp 34 km
21 miles
105,300 km
65,430 miles
23 hours 2013 Mark Robert Showalter and team Inner
Proteus 420 km (436 x 416 x 402 km)
261 miles
117,647 km
73,102 miles
27 hours 1989 Voyager Imaging Team Inner
Triton 2,707 km
1,682 miles
354,760 km
220,437 miles
141 hours 1846 William Lassell Major
Nereid 340 km
211 miles
5,513,400 km
3,425,861 miles
360 days 1949 Gerard Kuiper Prograde
Halimede 62 km
39 miles
15,730,000 km
9,774,150 miles
1880 days 2002 Matthew J. Holman, J. J. Kavelaars, Tommy Grav, Wesley C. Fraser, Dan Milisavljevic Retrograde
Sao 44 km
27 miles
22,420,000 km
13,931,115 miles
2914 days 2002 Matthew J. Holman, J. J. Kavelaars, Tommy Grav, Wesley C. Fraser, Dan Milisavljevic Prograde
Laomedeia 42 km
26 miles
23,570,000 km
14,645,691 miles
3168 days 2002 Matthew J. Holman, J. J. Kavelaars, Tommy Grav, Wesley C. Fraser, Dan Milisavljevic Prograde
Psamathe 38 km
24 miles
46,700,000 km
29,017,979 miles
9117 days 2003 Scott S. Sheppard, David C. Jewitt, Jan Kleyna Retrograde
Neso 60 km
37 miles
48,390,000 km
30,068,094 miles
9374 days 2002 Matthew J. Holman, Brett J. Gladman and teams Retrograde
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