What is neptunes atmospheric composition?
Its around 79% Hydrogen, 19% Helium and 1.5-2% Methane. The methane absorbs red light and give the planet its blue colour.
Atmospheric composition of Neptune by volume: Molecular hydrogen, H2: 80 percent Helium: 19 percent Methane 1.5 percent Hydrogen Deuteride: 192 parts per million ( approx. 0.019 percent) Ethane: 1.5 parts per million Ammonia ice, water ice, ammonia hydrosulfide, and methane ice also compose Neptune's atmosphere. Source: Space.com and Wikipedia