Neptune is known to possess thirteen moons. The planet has the greatest “hill sphere” or gravitational sphere of influence among all the other planets in the solar system. It is most likely because of its immense distance from the sun. The moons of Neptune had been the object of controversies due to their strangely uneven mass distribution. The biggest moon which is Triton makes up 97.7% of the total mass of the whole Neptunian moon system and the rest is made up by the other 12 moons altogether.

The largest and the first to be discovered satellite is Triton. Its radius of 2,706.8 km long makes it belong to the seven moons in the solar system which is larger than Pluto. Its discovery by William Lassel in 1846 was just seven days late than the first official sighting of its orbited planet. There are few different theories that scientists have brought up regarding the origin of Triton. Since it is large and massive enough that it is able to have adequate hydrostatic equilibrium, it was said that it could be a dwarf planet if only it was orbiting the Sun. Uniquely, Triton spins against the direction that Neptune revolves in. This means that it possibly could have been orbiting the Sun before it was captured by Neptune. Furthermore, an idea was brought up that Triton could be part of a three-body encounter. Triton might have existed with a binary planet (like Pluto and its largest moon Charon); the pair could have wandered too close to Neptune and caused Triton to be caught by Neptune’s gravitational force. Likely, the other satellites of Neptune could be the rubbles that resulted from the possibly chaotic capture of Triton. The known ways of how a planet normally captures a satellite can hardly be applied to Triton because of its hugeness and strange orbital motion. Moreover, this moon may have an active core. This can be proven by the ice and geysers present on its surface. These geysers shoot ice 8km high towards Triton’s narrow atmosphere. The presence of ice leads to the thinking that water and even life may be present.

There are 6 regular satellites inward of Triton. Some of them orbit among Neptune’s rings. Naiad, Thalassa and Despina orbits in between the rings. The second moon found is Nereid. It was discovered in 1949 by Gerard Kuiper. It’s one of the six irregular outer moons of Neptune. These outer moons have high inclinations and their orbits are a mixture of prograde and retrograde. Despina, Galatea, Larissa, Naiad, Proteus and Thalassa were sighted by the spacecraft Voyager 2 in 1989. The other five moons were just found recently; three in 2002 and two more in 2003. Psamathe and Neso, found in 2002 and 2003 respectively, have the widest orbits among all the satellites in the solar system – that is, about 125 times the distance between the Earth and the Moon. They are large enough that these two satellites would take 25 years for them to orbit around Neptune.

Neptune’s moons are named after aquatic idols in Greek and Roman mythology. Most of them are names of sea nymphs or “Nereids”. It is in keeping with Neptune’s position as god of the sea.

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