Despina (moon)

Despina
Despina as seen by Voyager 2 (smeared horizontally)
Discovery[1]
Discovered byStephen P. Synnott and Voyager Imaging Team
Discovery dateJuly 1989
Designations
Designation
Neptune V
Pronunciation/dəˈspaɪnə, dəˈspiːnə, 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
Dimensions(180±6) × (148±12) × (128±6) km[4]
75±3 km[4]
Volume~1.8×106 km3[a]
Mass~(0.71–1.4)×1018 kg[b]
Mean density
0.4–0.8 g/cm3[5]
~0.006–0.023 m/s2[c]
~0.032–0.054 km/s[d]
synchronous
zero
Albedo0.09[4][6]
Temperature~51 K mean (estimate)
22.0[6]

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.

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 150 kilometres (93 mi).[4] 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.[9]

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.[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. ^ Volume derived from the long axis A, the medium axis B and the short axis C:
  2. ^ Mass derived from density ρ and the volume V:
  3. ^ Surface gravity derived from the mass m, the gravitational constant G and the radius r:
  4. ^ Escape velocity derived from the mass m, the gravitational constant G and the radius 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. ^ a b c d 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. ^ Zhang, Ke; Hamilton, Douglas P. (2008-01-01). "Orbital resonances in the inner neptunian system: II. Resonant history of Proteus, Larissa, Galatea, and Despina". Icarus. 193 (1): 267–282. Bibcode:2008Icar..193..267Z. doi:10.1016/j.icarus.2007.08.024. ISSN 0019-1035.
  6. ^ a b "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. ^ 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.
  10. ^ Belyakov, Matthew; Davis, M. Ryleigh; Milby, Zachariah; Wong, Ian; Brown, Michael E. (2024-05-01). "JWST Spectrophotometry of the Small Satellites of Uranus and Neptune". The Planetary Science Journal. 5 (5): 119. arXiv:2404.06660. Bibcode:2024PSJ.....5..119B. doi:10.3847/PSJ/ad3d55. ISSN 2632-3338.
  11. ^ "Despina | astronomy". Encyclopedia Britannica. Retrieved 2020-11-08.