Astronomy:Despina (moon)

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Short description: Moon of Neptune
Despina
Despina.jpg
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/dəˈspaɪnə, dəˈspiːnə, dɛ-/
Named afterΔέσποινα Despœna
AdjectivesDespinian
Orbital characteristics[2][3]
Epoch 18 August 1989
52 525.95  km
Eccentricity0.00038 ± 0.00016
Orbital period0.33465551 ± 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 radius78.0 ± 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]
Rotation periodsynchronous
Axial tiltzero
Albedo0.09[4][6]
Physics~51 K mean (estimate)
Apparent magnitude22.0[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 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. doi:10.1086/423037. Bibcode: 2004AJ....128.1412J. 
  3. ↑ 3.0 3.1 Showalter, M. R.; de Pater, I.; Lissauer, J. J.; French, R. S. (2019). "The seventh inner moon of Neptune". Nature 566 (7744): 350–353. doi:10.1038/s41586-019-0909-9. PMID 30787452. PMC 6424524. Bibcode: 2019Natur.566..350S. https://www.spacetelescope.org/static/archives/releases/science_papers/heic1904/heic1904a.pdf. 
  4. ↑ 4.0 4.1 Karkoschka, Erich (2003). "Sizes, shapes, and albedos of the inner satellites of Neptune". Icarus 162 (2): 400–407. doi:10.1016/S0019-1035(03)00002-2. Bibcode: 2003Icar..162..400K. 
  5. ↑ Williams, Dr. David R. (2008-01-22). "Neptunian Satellite Fact Sheet". NASA (National Space Science Data Center). http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptuniansatfact.html. 
  6. ↑ 6.0 6.1 6.2 "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. http://ssd.jpl.nasa.gov/?sat_phys_par. 
  7. ↑ Marsden, Brian G. (August 2, 1989). "Satellites of Neptune". IAU Circular 4824. http://www.cbat.eps.harvard.edu/iauc/04800/04824.html. Retrieved 2011-10-26. 
  8. ↑ Marsden, Brian G. (September 16, 1991). "Satellites of Saturn and Neptune". IAU Circular 5347. http://www.cbat.eps.harvard.edu/iauc/05300/05347.html. Retrieved 2011-10-26. 
  9. ↑ "Where Are You From? - Credo Reference" (in en). http://search.credoreference.com/content/entry/philipsastronomy/despina/0. 
  10. ↑ Banfield, Don; Murray, Norm (October 1992). "A dynamical history of the inner Neptunian satellites". Icarus 99 (2): 390–401. doi:10.1016/0019-1035(92)90155-Z. Bibcode: 1992Icar...99..390B. 
  11. ↑ "Despina | astronomy" (in en). https://www.britannica.com/topic/Despina. 

External links



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