Thalassa is a moon of Neptune, part of the Solar System in the universe. Neptune is a planet associated with the Sun, our star, and this space encyclopedia describes the moon’s identity and place in its planetary system.

Thalassa — A natural satellite of Neptune. Its physical properties and orbital motion are shown from the available catalogue and ephemeris data.

No object-specific chemical/elemental dataset has been verified and imported for this record. This does not mean none is publicly available. Appearance may be imagined; chemistry is not.

Discovery and designation
Thalassa was discovered in 1989. JPL credits Voyager Science Team. Its provisional designation is S/1989 N5. The name and discovery entry identify this particular satellite of Neptune; similarly named asteroids are separate objects.

Thalassa was discovered in August 1989 in images taken by Voyager 2.

Thalassa, like Naiad, most likely formed from fragments of Neptune's original moons, which were smashed by the disturbances caused when the ice giant Neptune captured Triton. Thalassa is unusual for an irregular moon because it is roughly disk-shaped.

Also like Naiad, Thalassa circles the planet in the same direction as Neptune rotates, and remains close to Neptune's equatorial plane. Thalassa's orbit is slowly decaying due to tidal deceleration and may eventually crash into Neptune's atmosphere or be torn apart and form a planetary ring.

Thalassa was named after a daughter of Aether and Hemera from Greek mythology. Thalassa is also the Greek word for sea. The moon was originally designated as S/1989 N 5.