Thalassa (moon)

A simulated view of Thalassa orbiting Neptune.

Thalassa (tha-las'-a, Greek Θάλασσα) is the second moon of Neptune. Thalassa 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 temporary designation S/1989 N 5. It is also designated Neptune IV.

The discovery was announced (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.

It is irregularly shaped and shows no sign of any geological modification. Since the Thalassian orbit is below Neptune's synchronous orbital radius, it is slowly decaying due to tidal forces and will one day break up into a planetary ring or impact on Neptune's surface.

  • Orbital radius: 50,075 km
  • Diameter: 108×100×52 km
  • Mass: 3.7×1017 kg
  • Estimated Density: 1.3 g/cm3
  • Orbital period: 0.311 d (7 h 30 min)
  • Orbital inclination: 0.200° (to Neptune's equator), 0.209° (to the local Laplace plane), 28.40° (to the ecliptic)



Neptune's natural satellites


Naiad | Thalassa | Despina | Galatea | Larissa | Proteus | Triton | Nereid
S/2002 N 1 | S/2002 N 2 | S/2002 N 3 | S/2003 N 1 | S/2002 N 4

see also: The Solar System

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