Neptune has 14 known moons, which are named for minor water deities in Greek mythology. By far the largest of them is Triton, discovered by William Lassell on October 10, 1846, 17 days after the discovery of Neptune itself; over a century passed before the discovery of the second natural satellite, Nereid. Neptune’s outermost moon Neso, which has an orbital period of about 26 Julian years, orbits further from its planet than any other moon in the Solar System.

Triton and Nereide were the only ones known until 1989. Triton is the most curious of the Neptune satellites. It is the only one among the big satellites of the solar system that revolves around Neptune in the opposite direction to that of the rotation of the planet (retrograde movement).