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Despina (moon)

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Despina
Despina as seen by Voyager 2 (smeared horizontally)
Discovery
Discovered byStephen P. Synnott[1] and Voyager Imaging Team
Discovery dateJuly 1989
Orbital characteristics[2]
Epoch 18 August 1989
52 526 ± 1 km
Eccentricity0.0002 ± 0.0002
0.33465551 ± 0.00000001 d
Inclination
  • 0.216 ± 0.014° (to Neptune equator)
  • 0.06° (to local Laplace plane)
Satellite ofNeptune
Physical characteristics
Dimensions180×148×128 km[3][4]
75 ± 3 km[5]
Volume~1.8×106km³
Mass~2.2×1018 kg
(based on assumed density)
Mean density
~1.2 g/cm³ (estimate)[5]
~0.026 m/s2[a]
~0.063 km/s[b]
synchronous
zero
Albedo0.09[3][5]
Temperature~51 K mean (estimate)
22.0[5]

Despina (/d[invalid input: 'ɨ']ˈspiːnə/ di-SPEE-nə or /d[invalid input: 'ɨ']ˈspaɪnə/ di-SPY-nə; Latin: Despœna,; Greek: Δέσποινα), also known as Neptune V, is the third closest inner satellite of Neptune. It is named after Despoina, a nymph who was a daughter of Poseidon and Demeter.

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.[6] 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. The name was given on 16 September 1991.[7]

A simulated view of Despina orbiting Neptune

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.[8]

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 deceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.

Notes

  1. ^ Surface gravity derived from the mass m, the gravitational constant G and the radius r: Gm/r2.
  2. ^ Escape velocity derived from the mass m, the gravitational constant G and the radius r: √2Gm/r.

References

  1. ^ Planet Neptune Data http://www.princeton.edu/~willman/planetary_systems/Sol/Neptune/
  2. ^ Jacobson, R. A.; Owen, W. M., Jr. (2004). "The orbits of the inner Neptunian satellites from Voyager, Earthbased, and Hubble Space Telescope observations". Astronomical Journal. 128 (3): 1412–1417. Bibcode:2004AJ....128.1412J. doi:10.1086/423037. {{cite journal}}: Invalid |ref=harv (help)CS1 maint: multiple names: authors list (link)
  3. ^ a b Karkoschka, Erich (2003). "Sizes, shapes, and albedos of the inner satellites of Neptune". Icarus. 162 (2): 400–407. Bibcode:2003Icar..162..400K. doi:10.1016/S0019-1035(03)00002-2. {{cite journal}}: Invalid |ref=harv (help)
  4. ^ Williams, Dr. David R. (2008-01-22). "Neptunian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2008-12-13.
  5. ^ a b c d "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-13.
  6. ^ Marsden, Brian G. (August 2, 1989). "Satellites of Neptune". IAU Circular. 4824. Retrieved 2011-10-26.
  7. ^ Marsden, Brian G. (September 16, 1991). "Satellites of Saturn and Neptune". IAU Circular. 5347. Retrieved 2011-10-26.
  8. ^ Banfield, Don; Murray, Norm (October 1992). "A dynamical history of the inner Neptunian satellites". Icarus. 99 (2): 390–401. Bibcode:1992Icar...99..390B. doi:10.1016/0019-1035(92)90155-Z. {{cite journal}}: Invalid |ref=harv (help)
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