 Photograph taken by NASA'sVoyager 2in 1989 |
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Discovered by | - Johann Galle
- Urbain Le Verrier
- John Couch Adams
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Discovery date | 23 September 1846 |
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Pronunciation | |
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Named after | LatinNeptunus, via FrenchNeptune |
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Adjectives | Neptunian (), Poseidean |
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Epoch J2000 |
Aphelion | 30.33 AU (4.54 billion km) |
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Perihelion | 29.81 AU (4.46 billion km) |
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Semi-major axis | 30.07 AU (4.50 billion km) |
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Eccentricity | 0.008678 |
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Orbital period | - 164.8 yr
- 60,195 days
- 89,666 Neptunian solar days
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Synodic period | 367.49 days |
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Average orbital speed | 5.43 km/s |
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Mean anomaly | 256.228° |
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Inclination | 1.770°to ecliptic 6.43° to Sun's equator 0.74° to invariable plane |
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Longitude of ascending node | 131.783° |
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Time of perihelion | 2042-Sep-04 |
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Argument of perihelion | 273.187° |
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Known satellites | 14 |
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Mean radius | 24,622±19 km |
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Equatorial radius | 24,764±15 km 3.883 Earths |
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Polar radius | 24,341±30 km 3.829 Earths |
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Flattening | 0.0171±0.0013 |
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Surface area | 7.6187×109 km2 14.98 Earths |
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Volume | 6.253×1013 km3 57.74 Earths |
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Mass | 1.02413×1026 kg 17.147 Earths 5.15×10−5 Suns |
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Mean density | 1.638 g/cm3 |
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Surface gravity | 11.15 m/s2 1.14 g |
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Moment of inertia factor | 0.23(estimate) |
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Escape velocity | 23.5 km/s |
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Rotation period | 0.67125 d 16 h 6 m 36 s (synodic; solar day) |
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Sidereal rotation period | 0.6713 day 16 h 6 min 36 s |
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Equatorial rotation velocity | 2.68 km/s (9,650 km/h) |
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Axial tilt | 28.32° (to orbit) |
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North poleright ascension | 19h57m20s 299.3° |
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North pole declination | 42.950° |
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Albedo | 0.290 (bond) 0.442 (geom.) |
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Surface temp. | min | mean | max |
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1 bar level | | 72 K (−201 °C) | |
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0.1 bar (10 kPa) | | 55 K (−218 °C) | |
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Apparent magnitude | 7.67 to 8.00 |
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Angular diameter | 2.2–2.4″ |
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Scale height | 19.7±0.6 km |
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Composition by volume |
- Gases:
- 80%±3.2%hydrogen (H2)
- 19%±3.2%helium (He)
- 1.5%±0.5%methane (CH4)
- ~0.019% hydrogen deuteride (HD)
- ~0.00015% ethane (C2H6)
- Ices:
- ammonia (NH3)
- water (H2O)
- ammonium hydrosulfide (NH4SH)
- methane ice (?) (CH4·5.75H2O)
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