Online Astronomy eText: Satellites (Moons)
The Satellites (Moons) of Neptune: Thalassa Link for sharing this page on Facebook
Image of Thalassa
Image of Thalassa, smeared due to relative motion of the moon and spacecraft during the exposure
(Image credit Voyager 2, 1989)

     Like all moons that have orbital periods shorter than the rotation rate of their planet, Thalassa must be slowly decelerating, and will eventually break up inside the Roche limit for Neptune, or disintegrate in Neptune's atmosphere.

Data for Thalassa

Discovered by R. Terrile from Voyager 2 images, 1989 (originally named S 1989 N5)
Named after a daughter of Aether and Hemera (presumably because it is the Greek word for "sea")
Orbital size 50075 km (about 31115 miles), about 25455 km (15815 miles) above Neptune's surface
Orbital eccentricity 0%
Orbital inclination 0.135 degrees
Orbital period 7h 30m = 0.311 days
Rotational period unknown but almost certainly synchronous
Diameter about 80 km (irregular in shape)
Density assumed about 1.3 g/cc, but probably wrong
Mass essentially unknown
Albedo (reflectivity) 4% (assumed, and probably wrong)