The real facts about Neptune

Neptune is the eighth planet from the Sun and the fourth largest (by diameter) of the planet. Neptune is smaller in diameter but bigger in mass than Uranus. Neptune's composition is almost certainly alike to Uranus': various "ices" and rock with about 15% hydrogen and a little helium. Like Uranus, but unlike Jupiter and Saturn, it can not have a distinct internal layering but rather to be more or less uniform in composition. But there is most expected a small core (about the mass of the Earth) of rock-strewn material. Its atmosphere is generally hydrogen and helium with a minute amount of methane.

Neptune's blue color is mainly the result of absorption of red light by methane in the atmosphere but there is a number of additional as-yet-unidentified chromophore which gives the clouds their rich blue tint. Like Jupiter and Saturn, Neptune has an inner heat source -- it radiates more than, twice as much energy as it receives from the Sun.

Neptune also has rings. Earth-based observations showed just faint arcs rather than complete rings, but Voyager 2's images showed them to be entire rings with bright clumps. One of the rings looks to have a curious twisted structure (right). Like Uranus and Jupiter, Neptune's rings are extremely dark but their composition is unknown.

Neptune's rings have been noted names: the outermost is Adams (which contains three important arcs now named Liberty, Equality and Fraternity), next is an unnamed ring co-orbital with Galatea, then Leverrier (whose outer extensions are called Lassell and Arago), and lastly the faint but broad Galle. Neptune's magnetic field is, like Uranus', oddly oriented and most likely generated by motions of conductive material (probably water) in its middle layers.