What are planets atmospheres made up of?

Answer 1

Of the planets of our solar system, the atmospheric compositions are thought to be:

Mercury - a very, very, very thin and highly variable atmosphere containing hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor, with a combined pressure level of about 10−14 bar (1 nPa). The extreme temperatures it experiences due to its proximity to the sun allow sodium, calcium, and potassium, which we normally think of as solids, to appear as vapor

Venus - primarily carbon dioxide with a few percent nitrogen. Massive clouds of sulfuric acid fog are also a significant feature of the atmosphere

Earth - about (rounded to the nearest percent)78% nitrogen, 21% oxygen, 1% argon with comparatively small amounts (less than 1%) of water vapor (~0.4% - 1% to 4% at the surface), carbon dioxide (~0.039%) and other gasses.

Mars - a thin atmosphere of about 95% carbon dioxide, 3% nitrogen, and 2% argon

Jupiter - a thick atmosphere that varies a great deal in composition with depth. Overall it is believed to be mostly hydrogen and helium with roughly 1/8 helium and most of the rest hydrogen. The atmosphere also contains small amounts of the noble gases, organic gases, nitrogen compounds, oxygen compounds, sulfur compounds and phosphorous compounds.

Saturn - a thick atmosphere that, like Jupiter varies greatly with depth, but which is, overall, ~96% hydrogen, 3% helium, 0.4% methane, 0.01% ammonia, and 0.01% hydrogen deuteride - "heavy water" vapor with a deterium (2H) atom in place of one of the proteum (1H) atoms that the form of hydrogen in nearly all terrestrial water.

Uranus - similar to Jupiter and Saturn, it is mostly hydrogen and helium. The currently accepted helium molar fraction, i.e. the number of helium atoms per molecule of hydrogen/helium, is 0.152 ± 0.033 in the upper troposphere, which corresponds to a mass fraction 0.262 ± 0.048. It also contains detectable amounts of water, methane, and ammonia.

Neptune - the atmosphere of this planet is also mostly hydrogen (~80%) and helium (~19%) with small amounts of methane (~1%), hydrogen deuteride (<0.02%), and ethane (< 0.0002%).

Pluto - which was once considered a planet, but is now classified as a "dwarf" planet appears to have a thin envelope of nitrogen, methane, and carbon monoxide gases, which are derived from the ices of these substances on its surface.