Info

neptune

Neptune
Discovery
Discovery date 23 September 1846[1]
Designations
Pronunciation /ˈnɛptn/
/ˈnɛptjn/[2]
Adjectives Neptunian
Orbital characteristics[6][a]
Epoch J2000
Aphelion 30.33 AU
(4,540 Gm)
Perihelion 29.81 AU
(4,460 Gm)
Semi-major axis
30.110387 AU
(4,504.45 Gm)
Eccentricity 0.009456
Orbital period
164.8 yr
60,182 d
89,666 Neptunian solar days[3]
Synodic period
367.49 days[4]
Average orbital speed
5.43 km/s[4]
Mean anomaly
256.228°
Inclination 1.767975° to ecliptic
6.43° to Sun's equator
0.72° to invariable plane[5]
Longitude of ascending node
131.784°
Argument of perihelion
276.336°
Known satellites 14
Physical characteristics
Mean radius
24,622±19 km[7][b]
Equatorial radius
24,764±15 km[7][b]
3.883 Earths
Polar radius
24,341±30 km[7][b]
3.829 Earths
Flattening 0.0171±0.0013
Surface area
7.6183×109 km2[8][b]
14.98 Earths
Volume 6.254×1013 km3[4][b]
57.74 Earths
Mass 1.0243×1026 kg[4]
17.147 Earths
5.15×105 Suns
Mean density
1.638 g/cm3[4][b]
Surface gravity
11.15 m/s2[4][b]
1.14 g
Moment of inertia factor
0.23[9]
Escape velocity
23.5 km/s[4][b]
Sidereal rotation period
0.6713 day[4]
16 h 6 min 36 s
Equatorial rotation velocity
2.68 km/s
9,660 km/h
Axial tilt
28.32° (to orbit)[4]
North pole right ascension
19h 57m 20s[7]
299.3°
North pole declination
42.950°[7]
Albedo

0.290 (bond)

0.41 (geom.)[4]
Surface temp.minmeanmax
1 bar level   72 K (−201 °C)[4]  
0.1 bar (10 kPa)   55 K[4]  
Apparent magnitude
8.02 to 7.78[4][10]
Angular diameter
2.2–2.4″[4][10]
Atmosphere[4]
Scale height
19.7 ± 0.6 km
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)