Galatea (Moon)

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Short description: Moon of Neptune
Galatea
Galatea moon.jpg
Galatea as seen by Voyager 2 (elongation is due to smearing)
Discovery
Discovered byStephen P. Synnott[1] and Voyager Imaging Team
Discovery dateJuly 1989
Designations
Designation
Neptune VI
Pronunciation/ɡæləˈtiːə/[2]
Named afterΓαλάτεια Galateia
AdjectivesGalatean[3]
Orbital characteristics[4][5]
Epoch 18 August 1989
Semi-major axis
61 952.57  km
Eccentricity0.00022 ± 0.00008
Orbital period0.42874431 ± 0.00000001 d
Inclination
  • 0.052 ± 0.011° (to Neptune equator)
  • 0.06° (to local Laplace plane)
Satellite ofNeptune
Groupring shepherd
Physical characteristics
Dimensions204×184×144 km (±~10 km)[6][7]
Mean radius87.4 ± 4.9 km[5]
Volume~2.8×106km3
Mass2.12 ± 0.08 ×1018 kg[8]
Mean density~0.75 g/cm3 (estimate)[9]
surface gravity
~0.018 m/s2[lower-alpha 1]
escape velocity
~0.056 km/s[lower-alpha 2]
Rotation periodsynchronous
Axial tiltzero
Albedo0.08[6][9]
Physics~51 K mean (estimate)
Apparent magnitude21.9[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

Galatea inside of a faint ring arc near Neptune

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

  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.

Since Galatea is irregularly shaped, the actual surface gravity and escape velocity will vary significantly between different positions on the surface.

References

  1. ↑ Planet Neptune Data http://www.princeton.edu/~willman/planetary_systems/Sol/Neptune/
  2. ↑ galatea (3rd ed.), Oxford University Press, September 2005, http://oed.com/search?searchType=dictionary&q=galatea  (Subscription or UK public library membership required.)
  3. ↑ AMIA (1999) Transforming health care through informatics
  4. ↑ 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. 
  5. ↑ 5.0 5.1 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. 
  6. ↑ 6.0 6.1 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. 
  7. ↑ 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. 
  8. ↑ 8.0 8.1 Porco, C.C. (1991). "An Explanation for Neptune's Ring Arcs". Science 253 (5023): 995–1001. doi:10.1126/science.253.5023.995. PMID 17775342. Bibcode: 1991Sci...253..995P. 
  9. ↑ 9.0 9.1 9.2 "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. http://ssd.jpl.nasa.gov/?sat_phys_par. 
  10. ↑ 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. 
  11. ↑ 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. 
  12. ↑ 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. 
  13. ↑ Namouni, F.; C. Porco (2002). "The confinement of Neptune's ring arcs by the moon Galatea". Nature 417 (6884): 45–7. doi:10.1038/417045a. PMID 11986660. Bibcode: 2002Natur.417...45N. http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v417/n6884/abs/417045a_fs.html. 

External links

  • Galatea Profile by NASA's Solar System Exploration
  • Neptune's Known Satellites (by Scott S. Sheppard)



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