Thalassa is the second moon of Neptune in order from the planet. Thalassa was discovered in September 1989 by the Voyager Imaging team. It is named after a daughter of Aether and Hemera in Greek mythology and is also known as Neptune IV. Like the five other inner moons discovered during the 1989 flyby of Voyager 2, Thalassa is among the darkest objects in the Solar System.
|discovery||1989, by Voyager 2|
|orbit semi-major axis||50,075 km (31,112 miles)|
|diameter||108 × 100 × 52 km (67 × 62 × 32 miles)|
|orbital period||0.311 day (7 hr 28 min.)|