Despina (moon)
Third-closest inner moon of Neptune, shepherd of the Le Verrier ring.
Despina (designated Neptune V) is the third-closest inner moon of Neptune. Its name comes from Despoina, a Greek goddess and daughter of Poseidon and Demeter.
The moon was discovered in late July 1989 from images captured by the Voyager 2 probe. Initially given the temporary designation S/1989 N 3, its discovery was announced on 2 August 1989 in IAUC 4824, which noted that ten frames taken over five days were used, implying a discovery date before July 28. The name Despina was assigned on 16 September 1991.
Despina is about 150 kilometers (93 miles) in diameter. It has an irregular shape and shows no signs of geological activity. It is thought to be a rubble pile formed from fragments of Neptune’s original satellites, which were broken apart by gravitational disturbances from Triton shortly after that moon was captured into a highly eccentric orbit. Its composition resembles other small inner Neptunian moons, with a strong absorption feature at 3.0 microns indicating water ice or hydrated silicate minerals. Its albedo is 0.09 at 1.4 microns, 0.1 at 2.0 microns, dropping to 0.03 at 3.0 microns, and rising to 0.07 at 4.6 microns.
Despina’s orbit lies just outside that of Thalassa and just inside the Le Verrier ring, which it shepherds. Because its orbit is below Neptune’s synchronous orbit radius, tidal forces are slowly causing it to spiral inward. Eventually, it may either crash into Neptune’s atmosphere or break apart into a planetary ring after crossing its Roche limit due to tidal stretching.
- Designation
- Neptune V
- Discovery date
- late July 1989
- Discovered by
- Voyager 2 probe
- Temporary designation
- S/1989 N 3
- Diameter
- approximately 150 kilometres (93 mi)
- Albedo at 1.4 microns
- 0.09
- Albedo at 2.0 microns
- 0.1
- Albedo at 3.0 microns
- 0.03
- Albedo at 4.6 microns
- 0.07
Lore & Background
Despina was discovered in late July 1989 from 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.
Despina's diameter is approximately 150 kilometres (93 mi). It 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.
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.
Reader's Guide
Despina's significance lies in its role as a shepherd moon for the Le Verrier ring, helping to maintain the ring's structure through gravitational interactions. Its irregular shape and lack of geological modification suggest it is a primordial rubble pile, offering clues about the violent history of Neptune's satellite system after Triton's capture. The moon's composition, indicated by spectral features of water ice or hydrated silicates, aligns it with other small inner Neptunian moons. Its inward spiral due to tidal deceleration highlights the dynamic evolution of moons within a planet's Roche limit, potentially leading to its destruction or impact with Neptune. Discovered by Voyager 2 in 1989, Despina remains a key object for understanding the formation and fate of inner planetary satellites.
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