NEPTUNE

Neptune was initially experiential by Galle and d'Arrest on 1846 Sept 23 very near to the locations independently predicted by Adams and Le Verrier from calculations based on the observed positions of Jupiter, Saturn and Uranus.

Neptune's composition is almost certainly similar to Uranus': various "ices" and rock with 15% hydrogen and a little helium. It has no distinct internal layering but rather to be more or less uniform in composition. But there is most likely a small core like the mass of the Earth of rocky material. Its atmosphere is mostly hydrogen and helium with a small amount of methane.

Neptune is in blue color because of absorption of red light by methane in the atmosphere but there is some additional as-yet-unidentified chromophore which gives the clouds their rich blue tint.

Neptune has been tripped by only one spacecraft, Voyager 2 on Aug 25 1989. But fortunately, recent ground-based and HST observations have added information.