The Martian atmosphere is primarily composed of:
Carbon Dioxide (CO2): 95%
Nitrogen (N2): 2.85%
Argon (Ar): 2%
Oxygen (O2): 0.174%
Carbon Monoxide (CO): 0.0747%
Water Vapor (H2O): 0.03% (variable)
Additionally, the Martian atmosphere contains trace amounts of:
Noble gases (e.g., neon, krypton, xenon)
Hydrogen (H2)
Sulfur dioxide (SO2)
Nitrogen oxides (NOx)
Methane (CH4)
Ozone (O3)
The atmosphere is very thin, with a maximum density of about 20 g/m³, which is only about 2% of Earth’s atmospheric density. The temperature is generally below zero, ranging from -125°C to 20°C (-200°F to 70°F).
Sources:
NASA’s Mars Atmosphere webpage
NASA Science: “The Five Most Abundant Gases in the Martian Atmosphere”
Earth How: “Mars Atmosphere Compared to Earth”
Mars - Atmosphere, Climate, Dust Storms (astronomical publication)
“Mars’ atmosphere: Facts about the composition and climate” (online article)
Well done. Many thanks.