Despina (moon)

Despina
	Despina as seen by Voyager 2 (smeared horizontally)
Discovery
Discovered by	Stephen P. Synnott and Voyager Imaging Team
Discovery date	July 1989
Designations
Designation	Neptune V
Pronunciation	/dəˈspaɪnə, dəˈspiːnə, dɛ-/
Named after	Δέσποινα Despœna
Adjectives	Despinian
Orbital characteristics
	Epoch 18 August 1989
Semi-major axis	52 525.95 km
Eccentricity	0.00038 ± 0.00016
Orbital period (sidereal)	0.33465551 ± 0.00000001 d
Inclination	0.216 ± 0.014° (to Neptune equator); 0.06° (to local Laplace plane);
Satellite of	Neptune
Physical characteristics
Dimensions	(180±6) × (148±12) × (128±6) km
Mean radius	75±3 km
Volume	~1.8×106 km3
Mass	~(0.71–1.4)×1018 kg
Mean density	0.4–0.8 g/cm3
Surface gravity	~0.006–0.023 m/s2
Escape velocity	~0.032–0.054 km/s
Synodic rotation period	synchronous
Axial tilt	zero
Albedo	0.09
Temperature	~51 K mean (estimate)
Apparent magnitude	22.0

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.

Notes

^ Volume derived from the long axis A, the medium axis B and the short axis C: ${\frac {\pi }{6}}ABC$
^ Mass derived from density ρ and the volume V: $V\rho$
^ Surface gravity derived from the mass m, the gravitational constant G and the radius r: ${\frac {Gm}{r^{2}}}$
^ Escape velocity derived from the mass m, the gravitational constant G and the radius r: ${\sqrt {\frac {2Gm}{r}}}$

References

^ Planet Neptune Data http://www.princeton.edu/~willman/planetary_systems/Sol/Neptune/
^ 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.
^ 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.
^ ^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.
^ 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.
^ ^a ^b "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-13.
^ Marsden, Brian G. (August 2, 1989). "Satellites of Neptune". IAU Circular. 4824. Retrieved 2011-10-26.
^ Marsden, Brian G. (September 16, 1991). "Satellites of Saturn and Neptune". IAU Circular. 5347. Retrieved 2011-10-26.
^ 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.
^ 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.
^ "Despina | astronomy". Encyclopedia Britannica. Retrieved 2020-11-08.

External links

[Volume-5] Volume derived from the long axis A, the medium axis B and the short axis C: ${\frac {\pi }{6}}ABC$

[Mass-6] Mass derived from density ρ and the volume V: $V\rho$

[Surface_gravity-8] Surface gravity derived from the mass m, the gravitational constant G and the radius r: ${\frac {Gm}{r^{2}}}$

[Escape_velocity-9] Escape velocity derived from the mass m, the gravitational constant G and the radius r: ${\sqrt {\frac {2Gm}{r}}}$

[Willman-Neptune-1] Planet Neptune Data http://www.princeton.edu/~willman/planetary_systems/Sol/Neptune/

[Jacobson2004-2] 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.

[Showalter2019-3] 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.

[Karkoschka2003-4] 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.

[ZhangHamilton2008-7] 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.

[jplssd-10] "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-13.

[IAUC_4824-11] Marsden, Brian G. (August 2, 1989). "Satellites of Neptune". IAU Circular. 4824. Retrieved 2011-10-26.

[IAUC_5347-12] Marsden, Brian G. (September 16, 1991). "Satellites of Saturn and Neptune". IAU Circular. 5347. Retrieved 2011-10-26.

[BanfieldMurray1992-13] 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.

[14] 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.

[15] "Despina | astronomy". Encyclopedia Britannica. Retrieved 2020-11-08.

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