Galatea (moon)

Galatea
	Galatea as seen byVoyager 2(elongation is due tosmearing)
Discovery
Discovered by	Stephen P. Synnottand Voyager Imaging Team
Discovery date	July 1989
Designations
Designation	Neptune VI
Pronunciation	/ɡæləˈtiːə/
Named after	ΓαλάτειαGalateia
Adjectives	Galatean
Orbital characteristics
	Epoch18 August 1989
Semi-major axis	61952.57 km
Eccentricity	0.00022 ± 0.00008
Orbital period (sidereal)	0.42874431 ± 0.00000001 d
Inclination	0.052 ± 0.011° (to Neptune equator); 0.06° (to localLaplace plane);
Satellite of	Neptune
Group	ring shepherd
Physical characteristics
Dimensions	(204±10) × (184±16) × (144±8) km
Mean radius	88±4 km
Volume	~2.8×106km3
Mass	1.94×1018kg
Meandensity	~0.69 g/cm3
Surface gravity	~0.012–0.025m/s2
Escape velocity	~0.05–0.06 km/s
Synodic rotation period	synchronous
Axial tilt	zero
Albedo	0.08
Temperature	~51Kmean (estimate)
Apparent magnitude	21.9

Galatea/ɡæləˈtiːə/,also known asNeptune VI,is the fourth-closestinner moonofNeptune.It is named afterGalatea,one of the fiftyNereidsofGreek legend,with whomCyclops Polyphemuswas vainly in love.

Discovery[edit]

Galatea was discovered in late July 1989 from the images taken by theVoyager 2probe.It was given the temporary designationS/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[edit]

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 fromTritonsoon after that moon's capture into a very eccentric initial orbit.^[12]

Orbit[edit]

Galatea's orbit lies below Neptune'ssynchronous orbitradius, so it is slowly spiralling inward due totidal decelerationand may eventually impact the planet or break up into a newplanetary ringsystem upon passing itsRoche limitdue totidal stretching.

Galatea appears to be ashepherd moonfor theAdams ringthat is 1,000 kilometres (620 mi) outside its orbit.Resonanceswith 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.^[14]^[7]

Notes[edit]

^ Volume derived from the long axisA,the medium axisBand the short axisC: ${\frac {\pi }{6}}ABC$
^ Density derived from massmand the volumeV: ${\frac {m}{V}}$
^ Surface gravity derived from the massm,thegravitational constantGand the radiusr: ${\frac {Gm}{r^{2}}}$
^ Escape velocity derived from the massm,thegravitational constantGand the radiusr: ${\sqrt {\frac {2Gm}{r}}}$

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 Datahttp:// princeton.edu/~willman/planetary_systems/Sol/Neptune/
^"galatea".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)
^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.PMC6424524.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 fromthe originalon 2013-11-01.Retrieved2008-12-13.
^ Marsden, Brian G. (August 2, 1989)."Satellites of Neptune".IAU Circular.4824.Retrieved2011-10-26.
^ Marsden, Brian G. (September 16, 1991)."Satellites of Saturn and Neptune".IAU Circular.5347.Retrieved2011-10-26.
^ 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.; 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[edit]

[Volume-7] Volume derived from the long axisA,the medium axisBand the short axisC: ${\frac {\pi }{6}}ABC$

[Density-10] Density derived from massmand the volumeV: ${\frac {m}{V}}$

[Surface_gravity-11] Surface gravity derived from the massm,thegravitational constantGand the radiusr: ${\frac {Gm}{r^{2}}}$

[Escape_velocity-12] Escape velocity derived from the massm,thegravitational constantGand the radiusr: ${\sqrt {\frac {2Gm}{r}}}$

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

[2] "galatea".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)

[3] AMIA (1999),Transforming health care through informatics

[Jacobson2004-4] 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.Bibcode:2004AJ....128.1412J.doi:10.1086/423037.

[Showalter2019-5] 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.PMC6424524.PMID 30787452.

[Karkoschka2003-6] 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.

[Madeira_&_GiuliattiWinter_2022-8] 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.

[9] Giuliatti Winter et al. (2020), as cited in Madeira & Giuliatti Winter (2022).^[7]

[jplssd-13] "Planetary Satellite Physical Parameters".JPL(Solar System Dynamics). 2008-10-24. Archived fromthe originalon 2013-11-01.Retrieved2008-12-13.

[IAUC_4824-14] Marsden, Brian G. (August 2, 1989)."Satellites of Neptune".IAU Circular.4824.Retrieved2011-10-26.

[IAUC_5347-15] Marsden, Brian G. (September 16, 1991)."Satellites of Saturn and Neptune".IAU Circular.5347.Retrieved2011-10-26.

[BanfieldMurray1992-16] 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.

[NamouniPorco-17] 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.

[Porco1991-18] 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.

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