Galatea (moon)

Short description: Moon of Neptune

Galatea

Galatea as seen by Voyager 2 (elongation is due to smearing)

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

Semi-major axis

| 61 952.57  km
Eccentricity| 0.00022 ± 0.00008
Orbital period| 0.42874431 ± 0.00000001 d
Inclination|

* 0.052 ± 0.011° (to Neptune equator)
* 0.06° (to local Laplace plane)

Satellite of| Neptune
Group| ring shepherd
Physical characteristics
Dimensions| 204×184×144 km (±~10 km)[6][7]
Mean radius| 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]

surface gravity

| ~0.018 m/s2[lower-alpha 1]

escape velocity

| ~0.056 km/s[lower-alpha 2]
Rotation period| synchronous
Axial tilt| zero
Albedo| 0.08[6][9]
Physics| ~51 K mean (estimate)
Apparent magnitude| 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.

## Contents

* 1 Discovery
* 2 Physical properties
* 3 Orbit
* 4 Notes
* 5 References
* 6 External links

## 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

| Wikimedia Commons has media related to Galatea (moon).

|

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

* v
* t
* e

Moons of Neptune

Generally listed in increasing distance from Neptune

Regular (inner)|

* Naiad
* Thalassa
* Despina
* Galatea
* Larissa
* Hippocamp
* Proteus

Triton|

* Triton (Atmosphere
* Geological features
* Sky)

Irregular|

* Nereid
* Halimede
* Sao
* Laomedeia
* Psamathe
* Neso

See also|

* Neptune trojans
* Rings of Neptune

* Book
* Category
* Portal

* v
* t
* e

Natural satellites of the Solar System

Planetary
satellites|

* Terrestrial
* Martian
* Jovian
* Saturnian
* Uranian
* Neptunian

Dwarf-planet
satellites|

* Plutonian
* Haumean
* Makemakean
* Eridian
* OR10
* Quaoaran
* Orcean

Minor-planet moons|

* Main belt binaries:
* Antiope
* Frostia
* Berna
* Tokai
* Ostro
* Balam
* Doppler
* Pauling
* Iwamoto
* Wolff
* Bettig
* Christophedumas
* Trojans:
* Patroclus–Menoetius
* Hektor–Skamandrios
* Iphthime
* Eurydamas
* TNOs:
* Huya
* Typhon–Echidna
* Lempo–Paha–Hiisi
* 2002 UX25
* Logos–Zoe
* Ceto–Phorcys
* Borasisi–Pabu
* Sila–Nunam
* Teharonhiawako–Sawiskera
* Salacia–Actaea
* 2002 WC19
* Altjira
* Varda–Ilmarë
* 2003 AZ84
* Gǃkúnǁʼhòmdímà–Gǃòʼé ǃHú
* Mors–Somnus
* Manwë–Thorondor
* ǂKá̦gára–ǃHãunu
* 2013 FY27

Ranked by size|

* Planetary-mass moon
* Ganymede
* largest: 5268 km / 0.413 Earths
* Titan
* Callisto
* Io
* Moon
* Europa
* Triton
* Titania
* Rhea
* Oberon
* Iapetus
* Charon
* Umbriel
* Ariel
* Dione
* Tethys
* Dysnomia
* Enceladus
* Miranda
* Vanth
* Proteus
* Mimas
* Ilmarë
* Nereid
* Hiʻiaka
* Actaea
* Hyperion
* ...

* Discovery timeline
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* v
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Neptune

* Outline of Neptune

Geography|

* Great Dark Spot
* Small Dark Spot
* Rings

NASA image of Neptune

Moons|

* Despina
* Galatea
* Halimede
* Hippocamp
* Laomedeia
* Larissa
* Naiad
* Nereid
* Neso
* Proteus
* Psamathe
* Sao
* Thalassa
* Triton

Astronomy|

| Discovery|

* Urbain Le Verrier
* Johann Gottfried Galle
* John Couch Adams
* Heinrich Louis d'Arrest
* William Lassell

|

General|

* Kuiper belt
* Neptune-crossing minor planets

Trojans|

* 2001 QR322
* 2004 KV18
* 2004 UP10
* 2005 TN53
* 2005 TO74
* 2006 RJ103
* (527604) 2007 VL305
* 2008 LC18
* 2011 HM102

Exploration|

| Past|

* Voyager 2 (1989 flyby)

|

Proposals|

* ODINUS
* Triton Hopper
* Argo
* Trident

Cancelled|

* Mariner Mark II
* Neptune Orbiter
* New Horizons 2

Related|

* Fiction
* Mythology

* Book
* Category
* Portal

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