Galatea (moon)
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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 | |
61 952.57 km | |
Eccentricity | 0.00022 ± 0.00008 |
0.42874431 ± 0.00000001 d | |
Inclination |
|
Satellite of | Neptune |
Group | ring shepherd |
Physical characteristics | |
Dimensions | 204×184×144 km (±~10 km)[6][7] |
87.4 ± 4.9 km[5] | |
Volume | ~2.8×106km3 |
Mass | 2.12 ± 0.08 ×1018 kg[8] |
Mean density | ~0.75 g/cm3 (estimate)[9] |
~0.018 m/s2[a] | |
~0.056 km/s[b] | |
synchronous | |
zero | |
Albedo | 0.08[6][9] |
Temperature | ~51 K mean (estimate) |
21.9[9] |
Galatea /ɡæləˈtiːə/, also known as Neptune VI, is the fourth-closest inner 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
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/Galatea_feat.jpg/250px-Galatea_feat.jpg)
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
Galatea 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]
Orbit
Galatea'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.[13] Galatea's mass has been estimated based on the radial perturbations it induces on the ring.[8]
Notes
- ^ Surface gravity derived from the mass m, the gravitational constant G and the radius r: Gm/r2.
- ^ Escape velocity derived from the mass m, the gravitational constant G and the radius r: √2Gm/r.
Since Galatea is irregularly shaped, the actual surface gravity and escape velocity will vary significantly between different positions on the surface.
References
- ^ 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.
- ^ a b 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 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.
- ^ Williams, Dr. David R. (2008-01-22). "Neptunian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2008-12-13.
- ^ a b 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.
- ^ a b c "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.
- ^ Namouni, F.; C. Porco (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.
External links
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