(The second value represents the quantity as a fraction of the terrestrial value.)
Mass 102.43e24 kg 17.147 GM 6.8351e6 km3/s2 17.15 Equatorial radius 24,766 km 3.883 Polar radius 24,342 km 3.830 Flattening 17.081e-3 5.03 Mean density 1,638 kg/m3 0.297 J2 4e-3 3.151 Surface gravity (equator) 11.00 m/s2 1.125 Escape velocity 23.5 km/s 2.10
Semimajor axis 4.4966e9 km 30.06 Sidereal period 60,189. d 164.79 Tropical period 59,799.9 d 163.73 Eccentricity 0.00858 0.514 Inclination 1.773 deg Synodic period 367.49 d Mean orbital velocity 4.75 km/s 0.159
Bond albedo 0.82 2.13 Visual geometric albedo 0.41 1.12 Visual magnitude V(1,0) -6.87 Solar irradiance 1.47 W/m2 0.00107 Black-body temperature 33.2 K 0.134
Epoch 1994.0 North pole (RA and Dec) 299.25 deg / 42.94 deg Obliquity 28.31 deg Argument of prime meridian 147.30 deg at epoch Sidereal rotation rate 536.3128492 deg/d Sidereal rotation period 16.11 h* Magnetic coordinates (as determined by the Voyager 2 Radio Science experiment)
Dipole strength 0.142 gauss-Rn3 Dipole tilt to spin axis 46.9 deg Longitude of tilt 288 deg (IAU convention) Dipole offset 0.55 RnNote: Rn denotes Neptunian radii, here defined to be 24,765 km
Surface pressure >> 100 bar Average temperature ~58 K Temperature at 1 bar ~72 K Density at 1 bar ~0.45 kg/m3 Wind speeds 0 to 200 m/s Scale height 19.1 to 20.3 km Mean molecular weight 2.53 to 2.69 g/mol Composition: Hydrogen (H2) 89% Helium (He) 11% Methane (CH4) ? ppm Aerosols: Ammonia ice; water ice; ammonia hydrosulfide; methane ice(?)
Epoch JD 2449360.5 Mean distance 30.167 AU Eccentricity 0.0062 Inclination 1.77 deg Longitude of ascending node 131.76 deg Longitude of perihelion 25.34 deg Mean longitude at epoch 291.62 deg