Thalassa (moon)

Thalassa  200px Naiad or Thalassa as seen by Voyager 2 (smearing has caused excessive elongation) Discovery Discovered by Richard J. Terrile and Voyager Imaging Team Discovered in September 1989 Orbital characteristicsEpoch 18 August  1989  Semi-major axis 50 075 ± 1 km  Eccentricity 0.0002 ± 0.0002  Orbital period 0.31148444 ± 0.00000006 d  Inclination 0.21 ± 0.02°  (to Neptune equator)
0.21° (to local Laplace plane) Is a moon of Neptune Physical characteristics Dimensions  108×100×52 km Mass ~3.5 kg (based on assumed density) Mean density ~1.2 g/cm3 (estimate) Rotation period assumed synchronous Axial tilt ~zero presumably  Albedo (geometric) 0.09 Surface temp. ~51 K mean (estimate) Atmosphere none

Thalassa or Neptune IV, is the second closest moon to Neptune. It was named after a daughter of Aether and Hemera from Greek mythology.
"Thalassa" is also the Greek word for "sea".

Thalassa was discovered sometime before mid-September, 1989 from the images taken by the Voyager 2 probe. It was given the designation S/1989 N 5. The discovery was said (IAUC 4867) on September 29, 1989, but the text only talks of "25 frames taken over 11 days", giving a discovery date of sometime before September 18. The name was given on 16 September 1991.

Thalassa is not a sphere and shows no sign of any geological changes. Unusually for a non-spherical moon, it appears to be oddly shaped not able to be explained.

 Other websites 
 Thalassa Profile  by NASA's Solar System Exploration

Category:Neptune's moons