ice giant
Neptune
The farthest planet from the Sun: a deep-blue ice giant with the fastest winds in the Solar System, found by mathematics before it was seen.
- Distance from Earth today
- 4.35 billion km29.08 AU · light: 4 h 2 min
- Distance from the Sun today
- 4.47 billion km29.88 AU
- As of
- 2 November 2026Live distance and chart →
Where it is today
Top view of the plane of Earth’s orbit, compressed distance scale. Open on the big map with the time slider →
Facts
- Diameter
- 49,528 km
- Mass
- 102 × 10²⁴ kg
- Density
- 1,638 kg/m³
- Surface gravity
- 11.0 m/s²
- Escape velocity
- 23.5 km/s
- Rotation period
- 16.1 h
- Length of day
- 16.1 h
- Mean distance from the Sun
- 4.52 billion km (30.18 AU)
- Perihelion
- 4.47 billion km
- Aphelion
- 4.56 billion km
- Orbital period
- 163.7 years
- Mean orbital velocity
- 5.4 km/s
- Orbital eccentricity
- 0.010
- Orbital inclination
- 1.8°
- Axial tilt
- 28.3°
- Mean temperature
- -200 °C
- Surface pressure
- no solid surface
- Known moons
- 16
- Rings
- yes
- Global magnetic field
- yes
Source of the figures: NASA Planetary Fact Sheet (public domain).
Discovery: 1846 – Johann Gottfried Galle, from predictions by Urbain Le Verrier
Description
Neptune was the first planet found by calculation: irregularities in the motion of Uranus led Urbain Le Verrier to predict its position, and Johann Galle spotted it in 1846 very close to the predicted place. It is an ice giant similar in size to Uranus, but with a more active atmosphere whose winds are the fastest measured on any planet. When Voyager 2 flew past in 1989 it photographed the Great Dark Spot, a huge storm that later disappeared, along with bright high clouds and a set of thin, clumpy rings. Its largest moon, Triton, orbits backwards and was probably captured from the Kuiper belt. Voyager 2 remains the only spacecraft to have visited the planet.
Moons
- Tritonmajor moonDiameter: 2,705 km
- Nereidirregular moonDiameter: 340 km
- Proteusinner moonDiameter: 416 km
- Larissainner moonDiameter: 192 km
We describe 4 of the 16 known moons (count from the NASA Planetary Fact Sheet) – the largest and most interesting.