Galatea /ɡæləˈtiːə/, also known as Neptune VI, is the fourth-closest inner moon of Neptune, and fifth-largest moon of Neptune. It is named after Galatea, one of the fifty Nereids of Greek legend, with whom Cyclops Polyphemus was vainly in love.
 | |
| Discovery | |
|---|---|
| Discovered by | Stephen P. Synnott[1] and Voyager Imaging Team |
| Discovery date | July 1989 |
| Designations | |
Designation | Neptune VI |
| Pronunciation | /ɡæləˈtiːə/[2] |
Named after | Γαλάτεια Galateia |
| Adjectives | Galatean[3] |
| Orbital characteristics[4][5] | |
| Epoch 18 August 1989 | |
| 61952.57 km | |
| Eccentricity | 0.00022 ± 0.00008 |
| 0.42874431 ± 0.00000001 d | |
| Inclination |
|
| Satellite of | Neptune |
| Group | ring shepherd |
| Physical characteristics | |
| Dimensions | (204±10) × (184±16) × (144±8) km[6] |
| 88±4 km[6] | |
| Volume | ~2.8×106 km3[a] |
| Mass | 1.94×1018 kg[8] |
Mean density | ~0.69 g/cm3[b] |
| ~0.012–0.025 m/s2[c] | |
| ~0.05–0.06 km/s[d] | |
| synchronous | |
| zero | |
| Albedo | 0.08[6][9] |
| Temperature | ~51 K mean (estimate) |
| 21.9[9] | |
Discovery
edit
Galatea was discovered in late July 1989 from the images taken by the Voyager 2 probe. It was given the temporary designation S/1989 N 4.[10] 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.[11]
Physical properties
editGalatea 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.[12]
Compositionally, Galatea 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 0.08 albedo at 1.4 and 2.0 microns, dropping to 0.04 at 3.0 microns, and increasing to 0.12 at 4.6 microns.[13]
Orbit
editGalatea's orbit lies below Neptune's synchronous orbit radius, so it is slowly spiralling inward due to tidal deceleration and may eventually impact the planet or break up into a new planetary ring system upon passing its Roche limit due to tidal stretching.
Galatea appears to be a shepherd moon for the Adams ring that is 1,000 kilometres (620 mi) outside its orbit. Resonances with Galatea in the ratio 42:43 are also considered the most likely mechanism for confining the unique ring arcs that exist in this ring.[14] Galatea's mass has been estimated based on the radial perturbations it induces on the ring.[15][7]
Notes
edit- ^ Volume derived from the long axis A, the medium axis B and the short axis C:
- ^ Density derived from mass m and the volume V:
- ^ Surface gravity derived from the mass m, the gravitational constant G and the radius r:
- ^ Escape velocity derived from the mass m, the gravitational constant G and the radius r:
Since Galatea is irregularly shaped, the actual surface gravity and escape velocity will vary significantly between different positions on the surface.
References
edit- ^ Planet Neptune Data http://www.princeton.edu/~willman/planetary_systems/Sol/Neptune/
- ^ "galatea". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ^ AMIA (1999), Transforming health care through informatics
- ^ 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 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.
- ^ a b Madeira, Gustavo; Winter, Silvia Maria Giuliatti (2022-04-21). "Numerical analysis of processes for the formation of moonlets confining the arcs of Neptune". Monthly Notices of the Royal Astronomical Society. 513 (1): 297–309. arXiv:2204.01063. doi:10.1093/mnras/stac944. ISSN 0035-8711.
- ^ Giuliatti Winter et al. (2020), as cited in Madeira & Giuliatti Winter (2022).[7]
- ^ a b "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Archived from the original on 2013-11-01. 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.
- ^ Namouni, F.; Porco, C. (2002). "The confinement of Neptune's ring arcs by the moon Galatea". Nature. 417 (6884): 45–7. Bibcode:2002Natur.417...45N. doi:10.1038/417045a. PMID 11986660. S2CID 4430322.
- ^ Porco, C.C. (1991). "An Explanation for Neptune's Ring Arcs". Science. 253 (5023): 995–1001. Bibcode:1991Sci...253..995P. doi:10.1126/science.253.5023.995. PMID 17775342. S2CID 742763.
External links
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