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moons of Neptune
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Triton
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Triton
Triton Voyager 2 image of Triton. This 14-frame composite image shows the satellite's near-equatorial cantaloupe terrain and network of fractures, the remnant southern hemisphere ice coverage, and the dark wind streaks within the ice-cap region.

moons of Neptune

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History

Neptune is the planet in the solar system that is farthest from the Sun; it has 16 known moons. The largest by far is Triton, which is nearly the size of Earth’s Moon. Triton is the only large moon of the solar system that travels around its planet in retrograde fashion; that is, it orbits Neptune in the opposite direction of the planet’s rotation. Triton is likely a captured Kuiper belt object and is similar in size, density, and surface composition to the dwarf planet Pluto. The other satellites of Neptune are much smaller bodies.

Triton was discovered shortly after Neptune in 1846. Nereid was discovered more than a century later in 1949. Voyager 2 discovered six moons during its 1989 flyby of Neptune. The rest of Neptune’s moons were discovered by telescopes on Earth. The moons of Neptune are named for characters from Greek or Roman mythology associated with Poseidon or his Roman counterpart, Neptune. The moons of Neptune are listed in order of their distance in kilometers from the planet, with their year of discovery, orbital period in days, and diameter in kilometers.

name year discovered distance from Neptune (km) orbital period (days)* diameter (km)
Naiad 1989 48,200 0.29 96 × 60 × 52
Thalassa 1989 50,100 0.31 108 × 100 × 52
Despina 1989 52,500 0.33 180 × 148 × 128
Galatea 1989 62,000 0.43 204 × 184 × 144
Larissa 1989 73,500 0.55 216 × 204 × 168
Hippocamp 2013 105,300 0.95 18.00
Proteus 1989 117,600 1.12 440 × 416 × 404
Triton 1846 354,800 5.88 R 2,706.80
Nereid 1949 5,513,900 360.13 340.00
Halimede 2002 16,590,500 1,879 R 62.00
Sao 2002 22,239,900 2,919 44.00
S/2002 N 5 2002 23,414,700 3,151 23.00
Laomedeia 2002 23,499,900 3,168 42.00
Psamathe 2003 47,646,600 9,149 R 40.00
Neso 2002 49,897,800 9,805 R 60.00
S/2021 N 1 2021 50,700,200 10,043 R 14.00
*The “R” following the orbital period means the orbit of that satellite is retrograde.
The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Erik Gregersen.
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