Mass of Neptune
| Value | 1.02413e26 kg |
| Status | Measured: ± 2.30e+21 kg (0.000022 relative) |
| Source | NASA planetary fact sheet; GM from Voyager 2 tracking and satellite orbits, divided by CODATA 2022 G |
| Categories | Astronomicalsolar-systemplanets |
| microgram | 1.0241300e+35 μg |
| milligram | 1.0241300e+32 mg |
| gram | 1.0241300e+29 g |
| kilogram | 1.0241300e+26 kg |
| metric tonne | 1.0241300e+23 t |
| ounce | 3.6125123e+27 oz |
| pound | 2.2578202e+26 lb |
| stone | 1.6127287e+25 st |
| US short ton | 1.1289101e+23 ton |
| grain | 1.5804741e+30 gr |
| unified atomic mass unit (dalton) | 6.1674550e+52 u |
Learning zone
Neptune was predicted before it was seen. Discrepancies in Uranus's orbit led Le Verrier to calculate the position of a perturbing body, and Galle at the Berlin Observatory found it on the first night of looking, 23 September 1846, less than a degree from the predicted spot. Galileo had recorded it as a star in 1613 without noticing it moved.
Slightly smaller than Uranus but appreciably more massive, Neptune has the highest density of the four giants and radiates 2.6 times the energy it receives from the Sun, driving the fastest winds in the solar system at over 2000 km/h. Its own gravity governs the Kuiper belt: Pluto and the plutinos are locked in a 3:2 resonance with Neptune's 165-year orbit, which is what keeps them from ever colliding with it.