Neptune’s Moons

Due to its great distance from the Earth, it is extremely difficult for us to see any of Neptune’s moons.  For that reason, most of its moons were not discovered until 1989. In this year NASA sent a satellite to explore Neptune and give us the first glimpse of its moons. Today we know of 14 moons. However, there are almost certainly much more orbiting Neptune we just haven’t seen them yet.

An actual image of Neptune with green on it's southern pole.

Spring 2002 on Neptune

Neptune was the Roman god of the sea and fresh water. Neptune’s counterpart is the Greek god Poseidon. Many of the names given to the moons of Neptune are names that belong to his children, and wives. Or they are other deities of water.

Inner Moons

An illustration showing Neptune's moons.

Diagram of some of the Inner moons of Neptune.


Naiad is the closest moon to the surface of Neptune.  It’s too small to keep a ball-like shape. Instead, it is irregularly shaped, it looks more like an asteroid. Voyager 2 discovered this moon in 1989 .
In Greek Mythology the Naiads were nymphs who lived in and took care of springs, rivers, and fountains. These nymphs were very attached to their homes. If a village settled near them, they would offer blessings and protection. As long as they weren’t offended.


One of Neptune’s moons, Thalassa is a small, irregularly shaped moon discovered in 1989 by Voyager 2,
Thalassa was a daughter of Aether and Hemera in Greek Mythology. She was the primeval goddess of the sea and birthed the storm gods.


The third of Neptune’s moons is Despina. Voyager 2 discovered this small icy moon in 1989. The name of this moon comes from the goddess Despoina. In Greek Mythology Despoina is the daughter of Neptune and Demeter.


Galatea is the fourth of Neptune’s moons.  It was also discovered by Voyager 2 in 1989.
Galatea was a Nereid, daughter of the sea god. The Cyclops Polyphemus was in love with her but she did not return his feelings. In another story, she was a statue created by Pygmalion, who falls in love with her.

Outer Moons


Discovered by Harold Reitsema and David J. Tholen, on May 24, 1981, Larissa is the fifth of Neptune’s moons.  Larissa is small and heavily cratered. Its cratered surface suggests that it is probably very old. 
Larissa was a nymph and daughter of Piasus. She and Poseidon had three sons, Achaios, Phthios, and Pelasgus


Proteus is the second largest of Neptune’s moons, but it is still not very big or very round.  That is because its gravity is not strong enough to pull it into a ball shape.
Proteus was the prophetic old man of the sea and shepherd of the sea’s flocks (e.g., seals). He was a subject of Poseidon. He knew the past, present, and future, but didn’t like telling what he knew.


Triton is by far the largest of Neptune’s moons. Despite its large size, Triton probably did not form around Neptune. Scientists believe that Triton was captured by Neptune’s gravity long ago. So where did this large moon form?  Many scientists today believe that Triton formed as a planet far out in the Solar System.  
Eventually, it was shaken from its orbit and sent in towards Neptune.  Because of Neptune’s large size and gravity, it captured Triton as it passed. Triton orbits around Neptune in the opposite direction of Neptune’s rotation.
Triton is slowly getting closer and closer to Neptune’s surface.  Eventually, in a very long time, this moon will crash into Neptune.
William Lassell discovered Triton in 1846. This moon was named after a merman and demigod of the sea, the son of Neptune and Amphitrite.


Nereid is the outermost of Neptune’s moons, and the third largest.  This moon, discovered in 1949 by Kuiper, has a strangely shaped orbit.  It orbits Neptune in a long skinny oval, not in a short fat oval like the other planets and moons of the Solar System. This strange orbit makes it almost certain that Nereid is a captured asteroid or comet. 
In Greek Mythology the Nereids were sea nymphs. The daughters of Nereus and Doris, there are 50 in total. They helped sailors on their voyages when they faced large storms. One of the better known Nereids was Thetis, the mother of the hero Achilles.

S/2004 N 1

The most recently found of Neptune’s moons is S/2004 N 1, discovered in July 2013. It’s about 12 miles across, making it the smallest of the moons. This little moon is so small and dim that it escaped detection by Voyager 2.
Mark Showalter discovered the moon on a whim when he was looking at Neptune’s rings. He was looking far beyond the rings and noticed a white speck about 65,400 miles from Neptune. He found S/2004 N 1 between the orbits of moons Larissa and Proteus. Mark Showalter plotted a circular orbit for the moon, which completes one revolution around Neptune every 23 hours.
<The orbit of Neptune’s new moon>

Other Great Resources

(Video) Why Does Neptune’s Moon, Triton, Orbit Backwards? By Science Channel:

(Video) US Astronomer Discovers New Neptune Moon

(Video) Uranus Vs. Neptune:


Written by: Monica Siegenthaler