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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.)
orbital eccentricity 0.0002
orbital inclination 0.21°
visual albedo 0.06

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   • Neptune, moons

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