海卫五1989

由航海家2号于1989年7月底所观测到，并于同年的8月2日公开成果；并给予S/1989 N 3的暂时编号，但公告只提及在5天内所拍摄到的10张照片，代表其发现时间约在7月28日前。正式名称则在1991年的9月16日的IAU通报内公告。

表面特征

海卫五的表面十分的凹凸不平；但是根据观察结果显示，似乎并不是因为地质运动所造成的。可能的造成原因是因为海王星捕获海卫一时，海卫一初期轨道的干扰；使卫星的碎片再度结合在一起，而形成海卫五。

海卫五的轨道在海卫四之外，但两者非常接近。同时，海卫五的轨道也在海王星环之下，也比海王星的同步轨道低。受潮汐力的影响，海卫五持续靠近海王星，未来有可能因为小于洛希极限而坠毁于海王星大气或是形成一个环。

Despina, also known as Neptune V, is the third-closest inner moon of Neptune. It is named after the Greek mythological character Despoina, a goddess who was a daughter of Poseidon and Demeter.

Discovery

Despina was discovered in late July 1989 from the images taken by the Voyager 2 probe. It was given the temporary designation S/1989 N 3. The discovery was announced (IAUC 4824) on 2 August 1989, and mentions "10 frames taken over 5 days", implying a discovery date of sometime before July 28. The name was given on 16 September 1991.

Physical characteristics

Despina's diameter is approximately 150 kilometres (93 mi). Despina 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 disrupted by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.

Compositionally, Despina appears to be similar to other small inner Neptunian satellites, with a deep 3.0 micron feature attributed to water ice or hydrated silicate minerals. It has a 0.09 albedo at 1.4 microns, 0.1 albedo at 2.0 microns, dropping to 0.03 at 3.0 microns, and increasing to 0.07 at 4.6 microns.

Orbit

Despina's orbit lies close to but outside of the orbit of Thalassa and just inside the Le Verrier ring and acts as its shepherd moon. As it is also below Neptune's synchronous orbit radius, it is slowly spiralling inward due to tidal deceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.