Despina (moon)

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Despina

Despina as seen by Voyager 2 (smeared horizontally)
Discovery
Discovered by	Stephen P. Synnott[1] and Voyager Imaging Team
Discovered in	July 1989
Orbital characteristics [2]
Epoch 18 August 1989
Semi-major axis	52 526 ± 1 km
Eccentricity	0.0002 ± 0.0002
Orbital period	0.33465551 ± 0.00000001 d
Inclination	0.216 ± 0.014° (to Neptune equator) 0.06° (to local Laplace plane)
Is a satellite of	Neptune
Physical characteristics
Dimensions	180×150×130 km [3]
Mass	~2.1×1018 kg (based on assumed density)
Mean density	~1.2 g/cm3 (estimate)
Rotation period	assumed synchronous
Axial tilt	~zero presumably
Albedo (geometric)	0.09 [3]
Surface temp.	~51 K mean (estimate)
Atmosphere	none

Despina (des-pee'-nə or sometimes des-pye'-nə, IPA: [dɛsˈpiːnə], IPA: [dɛsˈpaɪnə], Latin Despœna from Greek Δεσποίνη), or Neptune V, is the third closest inner satellite of Neptune. It is named after Despina, a nymph who was a daughter of Poseidon.

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 ^[4]. The discovery was announced (IAUC 4824) on August 2, 1989, but the text only talks of "10 frames taken over 5 days", giving a discovery date of sometime before July 28.

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 smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit ^[5].

Despina's orbit lies close to but outside of the orbit of Thalassa and just inside the Le Verrier ring. As it is also below Neptune's synchronous orbit radius, it is slowly spiralling inward 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.

[edit] References

1. ^ Planet Neptune Data http://www.princeton.edu/~willman/planetary_systems/Sol/Neptune/
2. ^ R.A. Jacobson and W.M. Owen Jr. (2004). "The orbits of the inner Neptunian satellites from Voyager, Earthbased, and Hubble Space Telescope observations". Astronomical Journal 128: 1412.
3. ^ ^{a b} E. Karkoschka (2003). "Sizes, shapes, and albedos of the inner satellites of Neptune". Icarus 162: 400.
4. ^ IAUC 4824 discovery IAUC circular
5. ^ D. Banfield and N. Murray (1992). "A dynamical history of the inner neptunian satellites". Icarus 99: 390.

v • d • e Moons of Neptune
Naiad · Thalassa · Despina · Galatea · Larissa · Proteus · Triton · Nereid · S/2002 N 1 · S/2002 N 2 · S/2002 N 3 · Psamathe · S/2002 N 4
Neptune Trojans • Rings of Neptune