Neptune is the eighth planet in our Solar System and orbits 4 504 000 000 kilometres (30.06AU) from the Sun. It has a diameter of 49 532 kilometres and is the fourth largest planet. Weighing 1.0247e26 kilograms, it is also the third heaviest planet.

Although Pluto is the final planet in our Solar System, it is not always the most distant. Because of Pluto's eccentric orbit, it sometimes crosses the orbit of Neptune making Neptune the planet furthest away from the Sun of a couple of years.

It is believed that Neptune's composition is probably similar to Uranus'. There would be various "ices" and rock, with approximately 15% hydrogen and some helium. Unlike Jupiter and Saturn, it will probably not have a distinct internal layering, but will be pretty much even in it's composition. There is most likely a small core (perhaps the mass of Earth) which will probably composed of rocky material.

Like Uranus, the atmosphere is mostly hydrogen, helium and a small amount of methane. The absorption of red light by methane in Neptune's atmosphere results in Neptune having a similar blue colour to Uranus. But there is some unidentified chromophore , which gives the clouds of Neptune their rich blue tint.

Neptune's magnetic field is much like Uranus' in that it is oddly oriented and is probably generated by motions of conductive material (water perhaps) in its middle layers.

Currently Neptune has 8 known satellites and 4 rings.