In many ways, NeptuneΓÇÖs structure is similar to UranusΓÇÖs: the planet consists of a rocky core of hot material, which merges with a layer of water; the water, in turn, merges with the cold, gaseous atmosphere of hydrogen, helium, and methane. The methane in the atmosphere absorbs red light and reflects blue, giving the planet its characteristic blue hue.
With a diameter of about 49,000 kilometers, Neptune is slightly smaller than Uranus, but it is likely denser and more massive. The planetΓÇÖs inner core is believed to be quite hot (7,000 degrees Kelvin) hotter even than the surface of the Sun. Temperatures in the upper atmosphere vary from 74 to 59 degrees Kelvin,
