Neptune is the eighth planet out from the Sun, varying in distance from 4456 to 4537 million km.
Neptune was discovered in 1846 because two mathematicians, John Couch Adams in England and Urbain le Verrier in France, worked out that it must be there because of the effect of its gravity on the movement of Uranus.
Neptune is so far from the Sun that its orbit lasts 164.79 Earth years. Indeed, it has not yet completed one orbit since it was discovered in 1846.
Like Uranus, Neptune has a surface of icy cold liquid methane (-210°C), and an atmosphere of hydrogen and helium.
This photo of Neptune was taken by the Voyager 2 spacecraft in 1989. The Great Dark Spot, and the little white tail of clouds, named Scooter by astronomers, are both clearly visible.
Neptune is the fourth largest planet. At 49,528 km across, it is slightly smaller than Uranus — but it is actually a little heavier. Like Uranus, its oceans of incredibly cold liquid methane make it a beautiful shiny blue, although Neptune’s surface is a deeper blue than that of Uranus. Again like Uranus, Neptune has a thin layer of rings. But Neptune’s are level, and not at right angles to the Sun. Neptune has a Great Dark Spot, like Jupiter’s Great Red Spot, where storms whip up swirling clouds.
Neptune’s moon Triton is the coldest place in the Solar System, with surface temperatures of -236°C. 105 Unlike Uranus, which is almost perfectly blue, Neptune has white clouds, created by heat inside the planet.
Neptune has the strongest winds in the Solar System, blowing at up to 700 m per second.
Neptune has eight moons, each named after characters from Ancient Greek myths – Naiad, Thalassa, Despoina, Galatea, Larissa, Proteus, Triton and Nereid.
Neptune’s moon Triton looks like a green melon, while its icecaps of frozen nitrogen look like pink ice cream. It also has volcanoes that erupt fountains of ice.