Proteus (moon)

Proteus
	Processed grayscale image of Proteus from Voyager 2, August 1989 (image processing date). The massive crater Pharos occupies much of the upper right, straddling Proteus's terminator
Discovery
Discovered by	Voyager 2 ; Stephen P. Synnott
Discovery date	June 16, 1989
Designations
Designation	Neptune VIII
Pronunciation	/ˈproʊtiəs/ PROH-tee-əs
Named after	Πρωτεύς or Πρωτέας, Prōteys or Prōteas
Alternative names	S/1989 N 1
Adjectives	Protean (/ˈproʊtiən/ PROH-tee-ən or /proʊˈtiːən/ proh-TEE-ən)
Orbital characteristics
	Epoch 18 August 1989
Periapsis	117584±10 km
Apoapsis	117709±10 km
Semi-major axis	117647±1 km (4.75 RN)
Eccentricity	0.00053±0.00009
Orbital period (sidereal)	1.12231477±0.00000002 d
Average orbital speed	7.623 km/s
Inclination	0.524° (to Neptune's equator) ; 0.026°±0.007° (to local Laplace plane)
Satellite of	Neptune
Physical characteristics
Dimensions	424 km × 390 km × 396 km;
Mean radius	209±8 km; 210±7 km
Surface area	554 200 km2
Volume	(3.4±0.4)×107 km3
Mass	≈ (1.55–3.10)×1019 kg; ≈ (2.60–5.20)×10−6 Earths
Mean density	≈ 0.46–0.91 g/cm3
Surface gravity	≈ 0.023–0.054 m/s2
Escape velocity	≈ 0.099–0.146 km/s
Synodic rotation period	synchronous
Axial tilt	zero
Albedo	0.096
Temperature	≈ 51 K mean (estimate)
Apparent magnitude	19.7

Proteus (/ˈproʊtiəs/ PROH-tee-əs), also known as Neptune VIII, is the second-largest Neptunian moon, and Neptune's largest inner satellite. Discovered by Voyager 2 in 1989, it is named after Proteus, the shape-changing sea god of Greek mythology.^[11] Proteus orbits Neptune in a nearly equatorial orbit at a distance of about 4.75 times the radius of Neptune's equator.^[3]

Despite being a predominantly icy body more than 400 km (250 mi) in diameter, Proteus's shape deviates significantly from an ellipsoid.^[6] It is shaped more like an irregular polyhedron with several slightly concave facets and relief as high as 20 km (12 mi). Its surface is dark, neutral in color, and heavily cratered.^[12] Proteus's largest crater is Pharos, which is more than 230 km (140 mi) in diameter. There are also a number of scarps, grooves, and valleys related to large craters.

Proteus is probably not an original body that formed with Neptune. It could have accreted later from the debris formed when the largest Neptunian satellite, Triton, was captured.^[13]

^ "Proteus". Lexico UK English Dictionary. Oxford University Press. Archived from the original on March 22, 2020.
^ "Protean". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ ^a ^b Cite error: The named reference Jacobson2004 was invoked but never defined (see the help page).
^ ^a ^b ^c ^d ^e ^f ^g Cite error: The named reference Stooke1994 was invoked but never defined (see the help page).
^ Cite error: The named reference Williams2008-nssdc was invoked but never defined (see the help page).
^ ^a ^b ^c Cite error: The named reference Croft1992 was invoked but never defined (see the help page).
^ ^a ^b ^c Cite error: The named reference Karkoschka2003 was invoked but never defined (see the help page).
^ "Proteus By The Numbers". solarsystem.nasa.gov/. Retrieved September 4, 2020.
^ ^a ^b Cite error: The named reference ZhangHamiltonII was invoked but never defined (see the help page).
^ ^a ^b Cite error: The named reference jplssd was invoked but never defined (see the help page).
^ Cite error: The named reference IAUC 5347 was invoked but never defined (see the help page).
^ Cite error: The named reference DumasSmithTerrile2003 was invoked but never defined (see the help page).
^ Cite error: The named reference Goldreich1989 was invoked but never defined (see the help page).

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[1] "Proteus". Lexico UK English Dictionary. Oxford University Press. Archived from the original on March 22, 2020.

[2] "Protean". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[Jacobson2004-3] Cite error: The named reference Jacobson2004 was invoked but never defined (see the help page).

[Stooke1994-4] ^ ^a ^b ^c ^d ^e ^f ^g Cite error: The named reference Stooke1994 was invoked but never defined (see the help page).

[Williams2008-nssdc-5] Cite error: The named reference Williams2008-nssdc was invoked but never defined (see the help page).

[Croft1992-6] Cite error: The named reference Croft1992 was invoked but never defined (see the help page).

[Karkoschka2003-7] Cite error: The named reference Karkoschka2003 was invoked but never defined (see the help page).

[NASA_BTN-9] "Proteus By The Numbers". solarsystem.nasa.gov/. Retrieved September 4, 2020.

[ZhangHamiltonII-10] Cite error: The named reference ZhangHamiltonII was invoked but never defined (see the help page).

[jplssd-15] Cite error: The named reference jplssd was invoked but never defined (see the help page).

[IAUC_5347-16] Cite error: The named reference IAUC 5347 was invoked but never defined (see the help page).

[DumasSmithTerrile2003-17] Cite error: The named reference DumasSmithTerrile2003 was invoked but never defined (see the help page).

[Goldreich1989-18] Cite error: The named reference Goldreich1989 was invoked but never defined (see the help page).

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Discovery
Processed grayscale image of Proteus from Voyager 2, August 1989 (image processing date). The massive crater Pharos occupies much of the upper right, straddling Proteus's terminator
Discovered by	Voyager 2 Stephen P. Synnott
Discovery date	June 16, 1989
Designations
Designation	Neptune VIII
Pronunciation	/ˈproʊtiəs/ PROH-tee-əs^[1]
Named after	Πρωτεύς or Πρωτέας, Prōteys or Prōteas
Alternative names	S/1989 N 1
Adjectives	Protean (/ˈproʊtiən/ PROH-tee-ən or /proʊˈtiːən/ proh-TEE-ən)^[2]
Orbital characteristics^[3]
Epoch 18 August 1989
Periapsis	117584±10 km
Apoapsis	117709±10 km
Semi-major axis	117647±1 km (4.75 R_N)
Eccentricity	0.00053±0.00009
Orbital period (sidereal)	1.12231477±0.00000002 d
Average orbital speed	7.623 km/s
Inclination	0.524° (to Neptune's equator) 0.026°±0.007° (to local Laplace plane)
Satellite of	Neptune
Physical characteristics
Dimensions	424 km × 390 km × 396 km^[4] ^[a]
Mean radius	209±8 km^[6] 210±7 km^[7]
Surface area	554 200 km²^[8]
Volume	(3.4±0.4)×10⁷ km³^[4]
Mass	≈ (1.55–3.10)×10¹⁹ kg^[b] ≈ (2.60–5.20)×10⁻⁶ Earths
Mean density	≈ 0.46–0.91 g/cm³^[9]^[c]
Surface gravity	≈ 0.023–0.054 m/s²^[d]
Escape velocity	≈ 0.099–0.146 km/s^[e]
Synodic rotation period	synchronous^[4]
Axial tilt	zero^[4]
Albedo	0.096^[10]^[7]
Temperature	≈ 51 K mean (estimate)
Apparent magnitude	19.7^[10]

Proteus (moon)

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