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Neptune V

Proper NameDespina
DesignationNeptune V
Primary PlanetNeptune
Family / ClassRegular moons
Orbital Period8 hours, 2 minutes
Distance from NeptuneSemi-Major Axis: 52,500 km (near circular orbit)
Rotation Period8 hours, 2 minutes (synchronous orbit)
Mean Diameter156 km
97 miles
NotesA small inner moon of Neptune, orbiting close to the planet within its faint ring system. Despina and its fellow moons Naiad and Thalassa likely represent the coalesced remains of an earlier system of moons disrupted by the capture of Neptune's major moon Triton.

A small inner moon of the planet Neptune, whose name follows the convention of naming Neptune's moons for mythological beings associated with the sea (in this case Despoina, daughter of Poseidon, the Greek name for Roman Neptune).

Despina is the third closest of Neptune's moons to the planet itself. With Naiad and Thalassa, it forms a group of three small moons orbiting within the two innermost rings of Neptune's extensive but tenuous ring system. Despina follows a path just within the second ring from the planet, the Le Verrier ring. It is thought that a fine spread of nateral runs inward from the Le Verrier ring to the innermost Galle ring. If so, then Despina and its two companions orbit within this fine ring material, some 50,000km above the cloudtops of Neptune.

Despina seems to have originated at the time when Neptune captured its massive moon Triton. Originally, Triton was probably a Kuiper Belt object like Pluto, but was pulled into the gravitational influence of the ice giant Neptune. This capture event was cataclysmic for Neptune's original moon system, breaking apart the existing moons, but their material eventually coalesced to form a new system of small moons. Despina is one of these: an irregular clump of rubble measuring 180km along its longest axis, and 128km along its shortest.

Because of it lies so close to the planet, Despina orbits Neptune quickly, completing a circuit of the planet once every eight hours and two minutes. Its rotation period is synchronous, so it always shows the same face to Neptune as it passes around the planet. Indeed, Despina's orbit is so close to Neptune that it may not be stable over the long term, and it is not unlikely that the moon will break apart to be absorbed into Neptune's ring system, or even fall into the planet itself, at some point in the distant future.


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