SpaceAbout Neptune
Neptune is a dark, cold ice giant whipped by supersonic winds, more than 30 times as far from the Sun as Earth. It was discovered in 1846, and its largest moon, Triton, was found seventeen days later. In 2011 Neptune completed its first orbit of the Sun since its discovery. It is the only planet not visible to the naked eye.
Source: NASA, read on 12 November 2026.
Neptune compared with Earth
Size. Neptune is 49,528 km across. That is 3.9 times the width of Earth (12,756 km). About 3.9 Earths would fit side by side across it. Its mass is 17.1 times Earth's.
Gravity and your weight. Gravity at its cloud tops is 11 m/s², against 9.8 on Earth. So things weigh 112% of what they do on Earth. Someone who weighs 50 kg on Earth would feel like 56.1 kg there. The giant planets have no solid surface to stand on, so the figure is for the level in the atmosphere where the pressure is 1 bar. Try your own weight in the weight calculator.
Day. Neptune turns once on its axis in 16.1 hours. From one noon to the next, its day lasts 16.1 hours.
Year. One trip round the Sun takes 59,800 Earth days, which is 163.75 Earth years. A ten-year-old on Earth would be 0.1 years old there, counting in that world's years. See the age calculator.
Distance. Neptune is on average 4,515 million km from the Sun, between 4,471.1 million km at its closest and 4,558.9 million km at its farthest. Sunlight takes 4.2 hours to arrive. That is 30.18 times Earth's distance.
Tilt and temperature. Its axis is tilted by 28.3°. A tilt like this gives it seasons, as on Earth (23.4°). The mean temperature in the fact sheet is −200 °C.
Moons, rings and magnetism. The fact sheet counts 16 moons for Neptune. Rings: yes. A global magnetic field: yes.
All the figures
| Diameter | 49,528 km |
|---|---|
| Mass | 102 × 10²⁴ kg |
| Density | 1,638 kg/m³ |
| Gravity | 11 m/s² |
| Escape velocity | 23.5 km/s |
| Rotation period | 16.1 hours |
| Length of day | 16.1 hours |
| Distance from the Sun | 4,515 million km |
| Closest | 4,471.1 million km |
| Farthest | 4,558.9 million km |
| Orbital period | 59,800 days |
| Orbital velocity | 5.4 km/s |
| Orbital inclination | 1.8° |
| Orbital eccentricity | 0.01 |
| Tilt of axis | 28.3° |
| Mean temperature | −200 °C |
| Surface pressure | Unknown |
| Moons | 16 |
| Rings | Yes |
| Global magnetic field | Yes |
Figures: NASA NSSDCA Planetary Fact Sheet, last updated by NASA on 18 March 2025, read on 12 November 2026. NASA rounds these values. Counts of moons change as new ones are confirmed.
Common questions
How big is Neptune compared with Earth?
Neptune is 49,528 km across, 3.88 times the diameter of Earth.
How long is a day on Neptune?
From noon to noon, a day on Neptune lasts 16.1 hours.
How many moons does Neptune have?
The NASA fact sheet read on 12 November 2026 gives 16.