The atmosphere of Mars is thin, cold, and mostly carbon dioxide. By volume the NASA fact sheet gives carbon dioxide 95.1%, nitrogen 2.59%, argon 1.94%, oxygen 0.16%, and carbon monoxide 0.06 percent. Water vapor is a trace, around 210 parts per million, and it moves with the season. [1]

Pressure is 6.36 mbar at the mean radius. Over a year it can run from 4.0 mbar to 8.7 mbar as carbon dioxide freezes onto the polar caps and then returns to the air. Viking 1 measured a higher local range, about 6.9 to 9 millibars, because it sat low. A person would still need a pressure suit. [1]

Temperature and wind

The average temperature is 214 K (-59 C). At the Viking 1 site the day-night range ran from about 184 K to 242 K, or -89 C to -31 C. The scale height, the vertical distance over which pressure falls by a factor of e, is 11 km. [1]

Winds at the Viking sites were a few meters per second in summer and about 17 to 30 meters per second in dust storms. The air is so thin that those speeds do not hit like a terrestrial gale. They do lift dust. The storms themselves are on Dust storms on Mars. [1]

Why it is thin

Mars is small, its gravity is modest, and it has no global magnetic field to stand off the solar wind. MAVEN measured gases leaving the top of the atmosphere from its arrival in September 2014 until contact was lost on 6 December 2025. NASA declared the mission over on 3 June 2026. [2] The evidence says the air was thicker in the distant past. How many bars it held, and when it thinned, are still argued. See Exploration of Mars for the mission, and Water on Mars for what a thicker air would have allowed.

Low places such as Hellas carry a taller column of air than the summit of Olympus Mons. Pressure, temperature, and the chance of frost all follow the topography.

What the air is not

It is not breathable. Oxygen is a trace. It is not a vacuum either: parachutes, heat shields, and helicopters have all used it. Ingenuity flew in this air 72 times before its mission ended in January 2024. The seasons that pump the pressure up and down are Seasons of Mars. [1]

See also

References

  1. NASA Goddard Space Flight Center. Mars Fact Sheet, atmospheric table. Updated 19 May 2025. https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
  2. NASA Science. MAVEN. Contact lost 6 December 2025. End of mission declared 3 June 2026. https://science.nasa.gov/mission/maven/

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