Of the 14 satellites of Neptune, the largest is Triton, which is in a retrograde (backward) orbit around the planet. Triton is the largest moon in the solar system to do this.
On July 15, a 14th moon of Neptune, provisionally called S/2004 N 1, was announced.
Neptune has seven inner moons. Their orbits lie among several faint rings and partial rings composed of dust and ice particles. Outwards from Neptune, the inner moons are Naiad, Thalassa, Despina, Galatea, Larissa, S/2004 N 1 and Proteus.
Next outward from Neptune, Triton is one of four moons in the solar system known to have an atmosphere. The thin nitrogen haze is thought to have evaporated off of the frozen surface.
Triton is Neptune's largest moon, at 1,677 miles (2,700 km) in diameter. Because Triton moves backward in its orbit, astronomers think the icy moon formed in the frozen Kuiper belt, located in the outer solar system. Later, Neptune's gravity captured Triton.
After Triton comes Nereid. At 211 miles (340 km) in diameter, Nereid is one of the largest irregular moons in the solar system. Irregular moons have orbits that are highly inclined to the planet's equator.
Much further out than Nereid orbit five outer moons, Halimede, Sao, Laomedeia, Neso and Psmathe. These irregular moons travel in highly tilted orbits.
- Photos of Neptune, The Mysterious Blue Planet
- Uranus And Neptune: The Mysterious Outer Giants | Video
- Photos from NASA's Voyager 1 and 2 Probes