Naiad (moon)

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Naiad

Naiad or Thalassa as seen by Voyager 2 (smearing has caused excessive elongation)
Discovery
Discovered by	Voyager Imaging Team
Discovered in	September 1989
Orbital characteristics
Semi-major axis	48 227 ± 1 km
Eccentricity	0.0004 ± 0.0003
Orbital period	0.2943958 ± 0.0000002 d
Inclination	5.25 ± 0.03° (to Neptune equator) 4.75° (to local Laplace plane)
Is a satellite of	Neptune
Physical characteristics
Dimensions
Mass	(based on assumed density)
Mean density	~1.2 g/cm3 (estimate)
Rotation period	assumed synchronous
Axial tilt	~zero presumably
Albedo (geometric)	0.07
Surface temp.	~51 K mean (estimate)
Atmosphere	none

A simulated view of Naiad orbiting Neptune with The Sun in the distance.

Naiad (nye'-əd [UK, US] or nay'-əd [US], IPA /ˈnaɪəd/, /ˈneɪəd/, Greek Ναϊάδ-ες), or Neptune III, is a moon of Neptune named after the Naiads of Greek legend.

Naiad was discovered sometime before mid-September, 1989 from the images taken by the Voyager 2 probe. The last moon to be discovered during the flyby, it was designated S/1989 N 6 [IAUC 4867] discovery IAUC circular. 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.

Naiad is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit .

Naiad orbits about 23,500 km above Neptune's cloud tops. Since this is below the synchronous orbit radius, its orbit is slowly decaying due to tidal decceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching. Naiad orbits Neptune well within its fluid Roche limit, and its density is expected to be low enough that it may be very close to its actual Roche limit already.

References