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Bulk Parameters,
Orbital Parameters, Observational Parameters, Mean
Orbital Elements, Magnetosphere, Atmosphere.
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| Neptune
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| Bulk Parameters | Neptune | Earth | Ratio (Neptune/Earth) |
| Mass (1024 kg) | 102.46 | 5.9736 | 17.147 |
| Volume (1010 km3) | 6254 | 108.321 | 57.74 |
| Equatorial Radius (km) | 24764 | 6378.1 | 3.883 |
| Polar radius (km) | 24341 | 6356.8 | 3.829 |
| Volumetric mean radius (km) | 24624 | 6371 | 3.865 |
| Ellipticity | 0.01708 | 0.00335 | 5.10 |
| Mean density (kg/m3) | 1638 | 5515 | 0.297 |
| Surface gravity (eq.) (m/s2) | 11.00 | 9.78 | 1.12 |
| Escape velocity (km/s) | 23.5 | 11.2 | 2.10 |
| GM (x 106 km3/s2) | 6.8351 | 0.3986 | 17.15 |
| Bond albedo | 0.290 | 0.306 | 0.95 |
| Visual geometric albedo | 0.41 | 0.367 | 1.12 |
| Visual magnitude V (1,0) | -6.87 | -3.86 | - |
| Solar irradiance (W/m2) | 1.51 | 1367.6 | 0.0011 |
| Black-body temperature (K) | 46.6 | 254.3 | 0.183 |
| J2 (x 10-6) | 3411. | 1082.63 | 3.151 |
| Orbital Parameters | Neptune | Earth | Ratio (Neptune/Earth) |
| Semimajor axis (106 km) | 4495.06 | 149.6 | 30.047 |
| Sidereal orbit period (days) | 60189. | 365.256 | 164.79 |
| Tropical orbit period (days) | 59799.9 | 356.242 | 163.73 |
| Perihelion (106 km) | 4444.45 | 147.09 | 30.216 |
| Aphelion (106 km) | 4545.67 | 152.10 | 29.886 |
| Synodic period (days) | 367.49 | - | - |
| Mean orbital velocity (km/s) | 5.43 | 29.79 | 0.182 |
| Max. orbital velocity (km/s) | 5.50 | 30.29 | 0.182 |
| Min. orbital velocity (km/s) | 5.37 | 29.29 | 0.183 |
| Orbital inclination (deg) | 1.769 | 0.000 | - |
| Orbit eccentricity | 0.0113 | 0.0167 | 0.677 |
| Sidereal rotation period (hrs) | 16.11* | 23.9345 | 0.673 |
| Length of day (hrs) | 16.11 | 24.0000 | 0.671 |
| Obliquity to orbit (deg) | 28.32 | 23.45 | 1.208 |
| Observational Parameters | |||
| Discoverer: | Johann Gottfried Galle (based on predictions by John Couch Adams and Urbain Leverrier) | ||
| Discovery Date: | 23 September 1846 | ||
| Apparent diameter from Earth | Maximum | 2.4 | |
| (seconds of arc): | Minimum | 2.2 | |
| Distance from Earth | Maximum | 4687.3 | |
| (106 km): | Minimum | 4305.9 | |
| Mean values at opposition from Earth: | Distance from Earth: 4347.31 x 10^6 km | Apparent diameter (seconds of arc): 2.3 | Apparent Visual magnitude: 7.8 |
| Mean Orbital Elements (J200) | |||
| Semimajor axis (A.U.) | 30.06896348 | ||
| Orbital eccentricity | 0.00858587 | ||
| Orbital inclination (deg) | 1.76917 | ||
| Longitude of ascending node | 131.72169 | ||
| Longitude of perihelion (deg) | 44.97135 | ||
| Mean Longitude (deg) | 304.88003 | ||
| Magnetosphere | Goddard Space Flight Center OTD (08) Model | ||
| Dipole field strength | 0.142 gauss - Rn3 | Rn = Neptune's radius | |
| Dipole tilt to rotational axis | 46.9 degrees | ||
| Longitude of tilt (deg) | 288 degrees (IAU convention) | ||
| Dipole offset (planet center to dipole center) distance: | 0.55 Rn | ||
| Atmosphere | |||
| Surface Pressure | >> 100 bars | ||
| Surface Density (at 1 bar): | ~0.45 kg/m3 | ||
| Scale Height | 19.1 - 20.3 km | ||
| Average temperature | ~58 K | ||
| Temperature at 1 bar: | ~72 K | ||
| Diurnal temperature range | |||
| Wind speeds | 0 - 200 m/s | ||
| Mean molecular weight | 2.53 - 2.69 g/mole | ||
| Atmospheric Composition: | major: | ||
| (uncertainty in parentheses) | Molecular Hydrogen - 80.0% (3.2%) | Helium - 19.0% (3.2%) | |
| Methane - 1.5 % (0.5%) | |||
| Minor (ppm): | Hydrogen Deuteride - ~192 | Ethane - ~1.5 | |
| Aerosols: | Ammonia ice, water ice, ammonia hydrosulfide, methane ice (?) | ||
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Fact sheet source from NSSDC/NASA |