Nereid (moon)

Nereid
	Nereid imaged by Voyager 2 in 1989
Discovery
Discovered by	Gerard P. Kuiper
Discovery date	1 May 1949
Designations
Designation	Neptune II
Pronunciation	/ˈnɪəriəd/ NEER-ee-əd
Named after	Νηρηΐδες Nērēḯdes
Adjectives	Nereidian or Nereidean (both /ˌnɛriˈɪdiən/ NERR-ee-ID-ee-ən)
Orbital characteristics
	Epoch 1 January 2020 (JD 2458849.5)
Observation arc	27,478 d (75.23 yr)
Semi-major axis	5,504,000 km (0.03679 AU)
Eccentricity	0.749
Orbital period (sidereal)	360.14 d (0.9860 yr)
Mean anomaly	318.0°
Mean motion	0° 59m 58.597s / day
Inclination	5.8° (to the ecliptic); 7.090° (to local Laplace plane)
Longitude of ascending node	326.0°
Argument of periapsis	290.3°
Satellite of	Neptune
Physical characteristics
Mean diameter	357±13 km
Flattening	≤0.23
Mass	3.57×1019 kg; (5.98×10−6 M🜨)
Mean density	1.5 g/cm3 (assumed)
Surface gravity	≈0.075 m/s2 (0.0076 g)
Synodic rotation period	11.594±0.017 h
Albedo	0.24
Temperature	≈50 K (mean estimate)
Apparent magnitude	19.2[citation needed]
Absolute magnitude (H)	4.4

Nereid, or Neptune II, is the third-largest moon of Neptune. It has the most eccentric orbit of all known moons in the Solar System.^[4] It was the second moon of Neptune to be discovered, by Gerard Kuiper in 1949.

^ Cite error: The named reference Kuiper 1949 was invoked but never defined (see the help page).
^ "Nereid". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ "nereidian, nereidean". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ ^a ^b ^c Cite error: The named reference JPL-SSD-Neptune was invoked but never defined (see the help page).
^ ^a ^b ^c ^d Cite error: The named reference Kiss2019 was invoked but never defined (see the help page).
^ Cite error: The named reference JPL-SSD-sat_phys was invoked but never defined (see the help page).
^ Cite error: The named reference MPC115892 was invoked but never defined (see the help page).

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[Kuiper_1949-1] Cite error: The named reference Kuiper 1949 was invoked but never defined (see the help page).

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

[3] "nereidian, nereidean". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[JPL-SSD-Neptune-4] Cite error: The named reference JPL-SSD-Neptune was invoked but never defined (see the help page).

[Kiss2019-5] Cite error: The named reference Kiss2019 was invoked but never defined (see the help page).

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

[MPC115892-8] Cite error: The named reference MPC115892 was invoked but never defined (see the help page).

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Discovery^[1]
Nereid imaged by Voyager 2 in 1989
Discovered by	Gerard P. Kuiper
Discovery date	1 May 1949
Designations
Designation	Neptune II
Pronunciation	/ˈnɪəriəd/ NEER-ee-əd^[2]
Named after	Νηρηΐδες Nērēḯdes
Adjectives	Nereidian or Nereidean (both /ˌnɛriˈɪdiən/ NERR-ee-ID-ee-ən)^[3]
Orbital characteristics^[4]
Epoch 1 January 2020 (JD 2458849.5)
Observation arc	27,478 d (75.23 yr)
Semi-major axis	5,504,000 km (0.03679 AU)
Eccentricity	0.749
Orbital period (sidereal)	360.14 d (0.9860 yr)
Mean anomaly	318.0°
Mean motion	0° 59^m 58.597^s / day
Inclination	5.8° (to the ecliptic) 7.090° (to local Laplace plane)^[4]
Longitude of ascending node	326.0°
Argument of periapsis	290.3°
Satellite of	Neptune
Physical characteristics
Mean diameter	357±13 km^[5]
Flattening	≤0.23^[a]
Mass	3.57×10¹⁹ kg (5.98×10⁻⁶ M_🜨)
Mean density	1.5 g/cm³ (assumed)^[6]
Surface gravity	≈0.075 m/s² (0.0076 g)
Synodic rotation period	11.594±0.017 h^[5]
Albedo	0.24^[5]
Temperature	≈50 K (mean estimate)
Apparent magnitude	19.2^{[citation needed]}
Absolute magnitude (H)	4.4^[7]