Composition of Neptunian Atmosphere
Neptune, the eighth and farthest known planet from the Sun, among the other planets in the Solar System has the fourth rank in radius after Jupiter, Saturn and Uranus and has the third rank in mass after Jupiter and Saturn. Its radius and mass are about 3.9 and 17 times as large as those of Earth. Neptune like Uranus is considered to be an ice giant which points out the fact that Neptune is a giant planet mostly composed of ices where here ices refer to compounds such as water, ammonia and methane which have elements heavier than hydrogen and helium and can be considered as volatiles when compared to silicate rocks or metals. The outer gaseous envelope of Neptune or Neptunian atmosphere is mostly composed of molecular hydrogen (about 80% by volume), helium (about 19% by volume) and methane (about 1.5% by volume). Neptunian atmosphere also contains layers of clouds where uppermost clouds are made of methane. Although vivid azure color of Neptune differs from the aquamarine or cyan color of Uranus, in both cases, absorption bands of methane at the visible and near-infrared regions of electromagnetic spectrum are thought to play the major role in giving these ice giants their blue hue while the cause of difference is yet unknown.