Neptune has eight known satellites, two of which can be observed from Earth. The largest and brightest is Triton. It was discovered in 1846 and is only slightly smaller than Earth’s moon (2705 km in diameter). Triton has a retrograde orbit, which means it orbits Neptune the opposite way to Neptune's rotation. Triton has an atmosphere of nitrogen with a small amount of methane.
Triton is slowly spiralling towards Neptune. In 10 to 100 million years is expected to be so close to Neptune that it will be pulled apart and form a sixth ring. Not much is known about Neptune’s other 7 satellites as they are very small.
Some Astronomers think that Pluto could have been one of Neptune’s moons that escaped it’s orbit. some even think that Pluto could still be one of Neptune’s moons due to the crossing of their orbits of the sun which leaves Neptune the furthest planet from the sun for about 2 years.
Satellite Radius (km) Mass (kg) Discoverer and Date Naiad 29 ? Voyager 2 1989 Thalassa 40 ? Voyager 2 1989 Despina 74 ? Voyager 2 1989 Galatea 79 ? Voyager 2 1989 Larissa 96 ? Voyager 2 1989 Proteus 209 ? Voyager 2 1989 Triton 1350 2.14*1022 Lassel 1846 Nereid 170 ? Kuiper 1949