Neptune has a total of 14 moons. The largest moon is Triton which was discovered by William Lassell just seventeen days after Neptune was found. Then it took one hundred years later to find the second moon, Nereid. The Hubble Telescope found the 14th moon in 2013.
Most of Neptune's moons are named after sea nymphs.
Neptune has a lot of moons who have unusual orbits. Triton which is the largest moon of Neptune, orbits in a retrograde orbit (which means Triton orbits or moves the opposite way from how Neptune spins).
Two moons, Psamathe (discovered in 2002) and Neso (discovered in 2003), are also unusual because they have the largest orbits for any moons discovered in the solar system so far. They take about 25 years to make one orbit and are 125 times farther than how our Moon orbits away from Earth.
How Neptune's moons formed
Many astronomers and scientists think that Neptune's inner moons were not original bodies that formed with Neptune, but were instead remains of debris from Triton that slowly built up together. Other scientists think that when Triton was captured by Neptune, Triton's mass and odd orbit caused Neptune's original moons to be destroyed by gravity, only to be reformed after Triton formed a stable orbit.
While many astronomers also agree that Triton was not an original moon of Neptune, some think that Triton was captured in a "three-body-encounter". What must have happened was that Triton was part of a binary pair1 with another unknown celestial body. The pair was then captured by Triton survived and the other object being affected by Neptune's gravity.
Another possible event had Halimede, which was discovered in 2002, was thought to been originally a piece of Nereid when the moon was possibly hit with another object, since both moons seemed to have the same gray colors. Also Halimede was also calculated that the moon had a high chance of colliding with Nereid in the past.
1Binary pairs are two astronomical objects orbiting closely to each other.
List of moons
The Neptunian moons are listed here by its orbital period, from shortest to longest. Triton, which is not only massive enough for its surface to have collapsed into a sphere, but is comparable in size to our own moon, is highlighted in purple. Irregular (captured) moons are shown in grey; prograde in light grey and retrograde in dark grey. (Triton is also thought to be captured.)
(96 × 60 × 52)
(108 × 100 × 52)
(180 × 148 × 128)
(204 × 184 × 144)
(216 × 204 × 168)
|6||Neptune XIV||S/2004 N 1||~18||n/a||104,200||0.9362||~ 0.0||~ 0.000||2013|
(436 × 416 × 402)
|8||Neptune I||Triton ♠||ˈtraɪtən||2,705.2 ± 4.8
(2,709 × 2,706 × 2,705)
|2,140,800 ± 5200||354,759||5.877||156.865||0.0||1846|
|9||Neptune II||Nereid||ˈnɪəriː.ɪd||340 ± 50||2,700||5,513,818||360.13||7.090||0.7507||1949|
|10||Neptune IX||Halimede ♠||ˌhælɨˈmiːdiː||62||16||16,611,000||1,879.08||112.712||0.2646||2002|
|13||Neptune X||Psamathe ♠||ˈsæməθiː||40||4.4||48,096,000||9,074.30||126.312||0.3809||2003|
|14||Neptune XIII||Neso ♠||ˈniːsoʊ||60||15||49,285,000||9,740.73||136.439||0.5714||2002|
The picture at the right shows the orbits of Neptune's irregular moons discovered so far. The eccentricity of the orbits is represented by the yellow segments (extending from the pericentre to the apocentre) with the inclination represented on Y axis. The satellites above the X axis are prograde, the satellites beneath are retrograde. The X axis is labelled in Gm (million km) and the fraction of the Hill sphere's (gravitational influence) radius (~116 Gm for Neptune).
Triton, the biggest moon following a retrograde but a quasi-circular orbit, also thought to be a captured satellite, is not shown. Nereid, on a prograde but very eccentric orbit is believed to be scattered during Triton's capture.
Some asteroids also have the same names as moons of Neptune: 74 Galatea, 1162 Larissa.
Note that Triton did not have an official name until the twentieth century. Although the name was suggested in 1880 by Camille Flammarion, it did not come into regular use until at least the 1930s. Usually, it was simply known as "the satellite of Neptune" (the second satellite, Nereid, was not discovered until 1949). One of the 14 moons is called Neptune.
List of Neptune's moons Facts for Kids. Kiddle Encyclopedia.