Make your own free website on
Moons of
[ Main I Statistics I Atmosphere I Moons I Missions I Other Info I Images I Links ]

Neptune's Moons
Written by Dane Atkinson

INTRO: In October of 1846, a month after Galle and d'Arrest first saw Neptune, William Lassell, a British Astronomer, discovered a satellite (moon) orbiting the planet Neptune. He named it Triton.

TRITON: Triton, the largest of Neptune's moons (almost the size of earth's moon) that circles the planet in a retrograde direction which is the direction opposite to the rotation of the planet it's orbiting, at a steeply inclined orbit of 157 degrees. That phenomenon led some astronomers to surmise that Neptune had captured Triton as it traveled through space several billion years ago.

With a surface temperature of -391 degrees F, it is the coldest temperature that you can find anywhere in our solar system. The pink-colored surface (probably due to a covering of frozen water, methane, and nitrogen mixed with dust) which appeared in photos taken by Voyager 2 during
it's fly-by in August of 1989 show that the surface area seems to be made up of sheets of what appears to be a frozen liquid (as hard as rock because of the cold surface) after erupting from deep within the core out of giant geysers. This means that the moon has volcanic activity. This is surprising as well as amazing to find in a place so far away from the sun. Scientists do not know how this moon could have this sort of activity, but they guess it could be duw to the sun penetrating through Triton's transparent surface and melting the ice from below, thereby causing a local pressure build-up of gas. Another possibility is this one: if Triton has a rocky core, it can generate it's own heat source internally.

The End of Triton: It is believed that Triton may end up being torn apart by Neptune's gravitational field 100 million years from now. This is because it is spinning in the wrong direction and this fact, when combined with that of the moon's strong tidal interaction with Neptune, the moon's orbit is slowly decaying. Currently, if it were possible to view Neptune from Triton, Neptune would appear as a large moon approximately 16 times larger than our moon if we were looking at it from earth. After this disaster takes place, parts of Triton's pieces would probably land on Neptune's surface and the other half would probably form another ring system around Neptune.

orbit: 354,760 km from Neptune
diameter: 2700 km
mass: 2.14e22 kg

NEREID: 103 years after the discovery of Neptune's moon Triton. In 1949, astronomer Gerard Kuiper discovered a second new moon called Nereid from Earth using a telescope.

Nereid's orbit is so highly eccentric its distance from Neptune varies from 1,353,600 to 9,623,700 kilometers, and it requires 360 days to orbit Neptune. This is the most eccentric orbit known of any planet or moon in our solar system.

orbit: 5,513,400 km distance from Neptune
diameter: 340 km
mass: unknown

OTHER MOONS: While Voyager 2 passed by Neptune, it observed and found out a vast amount of new information on Neptune and it's moons. It also discovered Neptune had 6 new moons. The new moons were:

Satellite DistanceRadius Mass Discoverer Date
(000 km)(km)(kg)
Naiad 4829?Voyager 21989
Thalassa5040?Voyager 2 1989
Despina 53 74 ? Voyager 2 1989
Galatea 62 79 ? Voyager 2 1989
Larissa 74 96 ? Voyager 2 1989
Proteus 118 209 ? Voyager 2 1989

Each moon was very small and strange in shape quite unlike a common sphere. It is unknown but there is a possibility that there could be other moons besides the 8 that we know of now.