Despina (moon)

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

Despina
Despina as seen by Voyager 2 (smeared horizontally)
Discovery
Discovered byStephen P. Synnott[1] and Voyager Imaging Team
Discovery dateJuly 1989
Designations
Designation
Neptune V
Pronunciation/dɪˈspaɪnə, dɪˈspiːnə, dɛ-/
Named after
Δέσποινα Despœna
AdjectivesDespinian
Orbital characteristics[2][3]
Epoch 18 August 1989
52 525.95  km
Eccentricity0.00038 ± 0.00016
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[4][5]
Mean radius
78.0 ± 4.7 km[3]
Volume~1.8×106 km³
Mass~2.2×1018 kg
(based on assumed density)
Mean density
~1.2 g/cm³ (estimate)[6]
~0.026 m/s2[lower-alpha 1]
~0.063 km/s[lower-alpha 2]
synchronous
zero
Albedo0.09[4][6]
Temperature~51 K mean (estimate)
22.0[6]

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.[7] 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.[8]

Physical characteristics

Despina's diameter is approximately 152 kilometres (94 mi).[9]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.[10]

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[11] 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.

A simulated view of Despina orbiting Neptune

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.
  3. Showalter, M. R.; de Pater, I.; Lissauer, J. J.; French, R. S. (2019). "The seventh inner moon of Neptune" (PDF). Nature. 566 (7744): 350–353. Bibcode:2019Natur.566..350S. doi:10.1038/s41586-019-0909-9. PMC 6424524. PMID 30787452.
  4. 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.
  5. Williams, Dr. David R. (2008-01-22). "Neptunian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2008-12-13.
  6. "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-13.
  7. Marsden, Brian G. (August 2, 1989). "Satellites of Neptune". IAU Circular. 4824. Retrieved 2011-10-26.
  8. Marsden, Brian G. (September 16, 1991). "Satellites of Saturn and Neptune". IAU Circular. 5347. Retrieved 2011-10-26.
  9. "Where Are You From? - Credo Reference". search.credoreference.com. Retrieved 2017-02-12.
  10. 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.
  11. "Despina | astronomy". Encyclopedia Britannica. Retrieved 2020-11-08.
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