Neptune  
Neptune from Voyager 2 with Great Dark Spot at left
Discovery
Discovered by
  • Urbain Le Verrier
  • John Couch Adams
  • Johann Galle
Discovery date September 23, 1846
Designations
Pronunciation
Adjective Neptunian
Orbital characteristics
Epoch J2000
Aphelion 4,553,946,490 km
30.44125206 AU
Perihelion 4,452,940,833 km
29.76607095 AU
Semi-major axis 4,503,443,661 km
30.10366151 AU
Eccentricity 0.011214269
Orbital period 60,190.03 days
164.79 years
89,666 Neptune solar days
Synodic period 367.49 day
Average orbital speed 5.43 km/s
Mean anomaly 267.767281°
Inclination 1.767975° to Ecliptic
6.43° to Sun’s equator
0.72° to Invariable plane
Longitude of ascending node 131.794310°
Argument of perihelion 265.646853°
Satellites 13
Physical characteristics
Equatorial radius 24,764 ± 15 km
3.883 Earths
Polar radius 24,341 ± 30 km
3.829 Earths
Flattening 0.0171 ± 0.0013
Surface area 7.6183×10
14.98 Earths
Volume 6.254×10
57.74 Earths
Mass 1.0243×10
17.147 Earths
Mean density 1.638 g/cm
Equatorial surface gravity 11.15 m/s
1.14 g
Escape velocity 23.5 km/s
Sidereal rotation
period
0.6713 day
16 h 6 min 36 s
Equatorial rotation velocity 2.68 km/s
9,660 km/h
Axial tilt 28.32°
North pole right ascension 19
299.3°
North pole declination 42.950°
Albedo 0.290 (bond)
0.41 (geom.)
Surface temp.
   1 bar level
   0.1 bar (10 kPa)
min mean max
72 K
55 K
Apparent magnitude 8.02 to 7.78
Angular diameter 2.2–2.4″
Atmosphere
Scale height 19.7 ± 0.6 km
Composition
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 (?)

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Neptune, which is released under the Creative Commons Attribution-Share-Alike License 3.0