Discovery | |||||||||||||
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Discovered by | |||||||||||||
Discovery date | 23 September 1846 | ||||||||||||
Designations | |||||||||||||
Pronunciation | US: /ˈnɛpuːn/ ( listen), UK: /-tjuːn/ | ||||||||||||
Named after | Latin Neptunus, via French Neptune | ||||||||||||
Adjectives | Neptunian (/nɛpˈtjuːniən/), Poseidean | ||||||||||||
Orbital characteristics | |||||||||||||
Epoch J2000 | |||||||||||||
Aphelion | Lua error in Module:Convert at line 272: attempt to index local 'cat' (a nil value). | ||||||||||||
Perihelion | Lua error in Module:Convert at line 272: attempt to index local 'cat' (a nil value). | ||||||||||||
Lua error in Module:Convert at line 272: attempt to index local 'cat' (a nil value). | |||||||||||||
Eccentricity | 0.008678 | ||||||||||||
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367.49 days | |||||||||||||
Average orbital speed | 5.43 km/s | ||||||||||||
259.883° | |||||||||||||
Inclination | 1.770° to ecliptic 6.43° to Sun's equator 0.74° to invariable plane | ||||||||||||
131.783° | |||||||||||||
2042-Sep-04 | |||||||||||||
273.187° | |||||||||||||
Known satellites | 16 | ||||||||||||
Physical characteristics | |||||||||||||
Mean radius | 24,622±19 km | ||||||||||||
Equatorial radius | 24,764±15 km 3.883 Earths | ||||||||||||
Polar radius | 24,341±30 km 3.829 Earths | ||||||||||||
Flattening | 0.0171±0.0013 | ||||||||||||
7.6187×109 km2 14.98 Earths | |||||||||||||
Volume | 6.253×1013 km3 57.74 Earths | ||||||||||||
Mass | 1.02413×1026 kg 17.147 Earths 5.15×10−5 Suns | ||||||||||||
Mean density | 1.638 g/cm3 | ||||||||||||
11.15 m/s2 1.14 g | |||||||||||||
0.23 (estimate) | |||||||||||||
23.5 km/s | |||||||||||||
0.67125 d 16 h 6 m 36 s | |||||||||||||
Sidereal rotation period | 0.6713 day 16 h 6 min 36 s | ||||||||||||
Equatorial rotation velocity | 2.68 km/s (9,650 km/h) | ||||||||||||
28.32° (to orbit) | |||||||||||||
North pole right ascension | 19h 57m 20s 299.3° | ||||||||||||
North pole declination | 42.950° | ||||||||||||
Albedo | 0.290 (bond) 0.442 (geom.) | ||||||||||||
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7.67 to 8.00 | |||||||||||||
−6.9 | |||||||||||||
2.2–2.4″ | |||||||||||||
Atmosphere | |||||||||||||
19.7±0.6 km | |||||||||||||
Composition by volume | |||||||||||||
Neptune is the eighth and farthest planet from the Sun in the Solar System. It is an ice giant. It is the fourth-largest planet in the system.
Neptune's mass is 17 times Earth's mass and a little bit more than Uranus' mass. Neptune is denser and smaller than Uranus. Because of its greater mass, Neptune's gravity makes its atmosphere smaller and denser.
It was named after the Roman god of the sea, Neptune. Neptune's astronomical symbol is ♆, the trident of the god Neptune.