The atmosphere of Mars

What is the atmosphere of Mars made of?

Mostly carbon dioxide: 95.1% by volume, NASA’s Mars fact sheet says. Nitrogen (2.59%) and argon (1.94%) make up most of the rest, and only 0.16% is oxygen.[1] Earth’s air is the other way around: mostly nitrogen and oxygen, with just 0.042% carbon dioxide.[2]

Gases by volume, from NASA’s Mars and Earth fact sheets (Earth: dry air, except water vapor). Methane from NASA’s Curiosity rover and ESA’s Trace Gas Orbiter. The density and mass comparisons are our calculation.[1][2][16][17]

What is the air pressure on Mars?

About 6.36 millibars on average, 0.6% of Earth’s 1,014 millibars.[1][2] It changes with the seasons, from about 4.0 to 8.7 millibars.[1] The air at the surface is far less dense too: about 0.016 kg per cubic meter, against 1.217 kg on Earth.[1][2]

Air that thin matters. Liquid water can’t last long on the surface, heat from the Sun escapes easily, and the air gives little protection from meteorites, NASA says.[3] Why the pressure rises and falls over a Mars year is explained on our Mars weather page.

Can you breathe on Mars?

No. “People would not be able to breathe the air on Mars,” NASA says.[4] There are two problems. The air is only 0.16% oxygen, against almost 21% on Earth, and the whole atmosphere presses down with less than 1% of Earth’s pressure.[1][2]

Outside, astronauts would need a spacesuit, which gives them a pressure garment, oxygen and carbon dioxide removal, NASA says. Its engineers expect a Mars suit to need a different way of getting rid of the carbon dioxide astronauts breathe out, because the air around them is itself mostly carbon dioxide.[5] What else living there would take is on our page can humans live on Mars?

Why did Mars lose its atmosphere?

Mostly because the solar wind and the Sun’s radiation stripped it away into space, NASA’s MAVEN mission found.[6] Billions of years ago Mars was much wetter and warmer, with a thicker atmosphere.[3] In 2017 the MAVEN team reported that about 65% of the argon ever in Mars’s air has been lost to space. “We’ve determined that most of the gas ever present in the Mars atmosphere has been lost to space,” said Bruce Jakosky, then MAVEN’s principal investigator. Most of the planet’s carbon dioxide went the same way.[6]

The solar wind is a stream of charged particles from the Sun. As it flows past Mars, it sets up an electric field that flings charged atoms from the upper atmosphere into space. In 2015 MAVEN measured that loss at about 100 grams (about 1/4 pound) every second, rising during solar storms. The young Sun was more active, so the loss was probably much faster billions of years ago.[7] In May 2025 the team reported the first direct sighting of “sputtering”, in which fast particles crash into the air and splash gas out into space, happening four times faster than predicted.[8]

MAVEN orbited Mars for more than 11 years. NASA last heard from it on Dec 6, 2025, and announced on Jun 3, 2026 that the mission had ended.[9] Losing air also meant losing water; where Mars’s water went has its own page.

Does Mars have a magnetic field?

Not a global one. Mars has no global magnetic field today, NASA says, but patches of crust in the southern hemisphere are strongly magnetized, traces of a field from 4 billion years ago.[3] NASA’s Mars Global Surveyor mapped them with its magnetometer, NASA reported in 1999: bands of magnetized rock lying side by side, each pointing the opposite way to its neighbor. The bands are about 160 km (100 mi) wide and 965 km (600 mi) long, and the longest stretches more than 1,930 km (1,200 mi).[10] They are strongest in the southern highlands around Terra Cimmeria and Terra Sirenum (NASA image PIA02819).[11]

The bands probably formed while Mars’s hot metal core worked as a dynamo and made a global field: as new crust cooled and hardened, the field was frozen into it. When the core cooled, the dynamo stopped and the global field vanished. The smooth northern lowlands carry almost no magnetism, a sign their crust formed after that.[10] Without a global field, NASA says, the atmosphere was left directly exposed to the solar wind and solar storms.[8]

What Mars has now is a “hybrid” magnetosphere, in NASA’s words: leftover fields in the crust plus a weaker field in the upper atmosphere. NASA’s twin ESCAPADE orbiters are built to study how the solar wind interacts with it and drives the planet’s atmospheric escape. They launched on Nov 13, 2025, and NASA plans for them to use Earth’s gravity to slingshot toward Mars in fall 2026.[12]

Is there oxygen on Mars?

Only a trace: 0.16% of the air.[1] But oxygen can be made from the carbon dioxide. MOXIE, an experiment on NASA’s Perseverance roverRoverA rover is a robot vehicle that drives across Mars, following plans its team on Earth sends ahead of each drive.More in the glossary, did it for the first time on Apr 20, 2021, making about 5 grams in its first run.[14] It splits one oxygen atom off each carbon dioxide molecule and vents the leftover carbon monoxide.[13][14]

By its 16th and final run, on Aug 7, 2023, MOXIE had made 122 grams (4.3 oz) of oxygen in all, about what a small dog breathes in 10 hours, NASA said. At its best it made 12 grams an hour, twice NASA’s original goal, at 98% purity or better.[13]

The main use would be rocket propellant. NASA said in 2021 that lifting four astronauts off Mars would take about 25 metric tons (55,000 lb) of oxygen. MOXIE’s principal investigator, Michael Hecht of MIT, said a crew spending a year on the surface might use about one metric ton between them for breathing.[14]

Is there methane on Mars?

Sometimes, in tiny amounts, and the instruments disagree. NASA’s Curiosity rover has repeatedly found methane just above the floor of Gale Crater: less than half a part per billion on average, with spikes of up to 20 parts per billion.[16] In 2018 NASA reported that the low background level peaks in the warm summer months and drops in winter, year after year.[15]

ESA’s ExoMars Trace Gas Orbiter, which looks from above, hasn’t detected any, NASA said in 2021.[16] Its first results, in April 2019, set an upper limit of 0.05 parts per billion, 10 to 100 times less than every earlier reported detection.[17]

One idea fits both. Curiosity measures mostly at night, when the air is calm and methane seeping from the ground could build up near the surface. The orbiter needs sunlight and looks about 5 km (3 mi) up, after the day’s warm, rising air has mixed it away. When Curiosity measured in daytime, the methane dropped to effectively zero, as predicted. That still leaves a puzzle: methane should last about 300 years on Mars, so scientists suspect something destroys it faster.[16]

On Earth, 95% of the methane in the air comes from living things, ESA says.[17] Reactions between rock, water and heat can make it too, and NASA says scientists can’t rule out a biological source on Mars.[15][16] The search is covered on our life on Mars page.

Does Mars have clouds?

Yes. Most Martian clouds are made of water ice and float no higher than about 60 km (37 mi). Higher, colder clouds are likely frozen carbon dioxide, or dry ice.[18] Dust hangs in the air too, which is why NASA says the sky would look hazy and red to our eyes, not blue. Winds sometimes raise dust storms that cover much of the planet, and the dust can take months to settle.[3] Why that dust is red is explained on our page why is Mars red?

Sources

1. NASA NSSDCA — Mars Fact SheetPrimary · checked Oct 6, 2026
2. NASA NSSDCA — Earth Fact SheetPrimary · checked Oct 6, 2026
3. NASA Science — Mars: FactsPrimary · checked Oct 6, 2026
4. NASA Space Place — All About MarsPrimary · checked Oct 6, 2026
5. NASA Johnson Space Center — Houston We Have a Podcast, Ep. 181: Suit Up for MarsPrimary · checked Oct 6, 2026
6. NASA — NASA’s MAVEN Reveals Most of Mars’ Atmosphere Was Lost to SpacePrimary · checked Oct 6, 2026
7. NASA — NASA Mission Reveals Speed of Solar Wind Stripping Martian AtmospherePrimary · checked Oct 6, 2026
8. NASA Science — NASA’s MAVEN Makes First Observation of Atmospheric Sputtering at MarsPrimary · checked Oct 6, 2026
9. NASA — NASA Says Farewell to MAVEN Mars Mission, Hosts Media Call TodayPrimary · checked Oct 6, 2026
10. NASA JPL — Magnetic Stripes Preserve Record of Ancient MarsPrimary · checked Oct 6, 2026
11. NASA Photojournal — PIA02819: Mars Crustal Magnetic Field RemnantsPrimary · checked Oct 6, 2026
12. NASA Science — ESCAPADEPrimary · checked Oct 6, 2026
13. NASA JPL — NASA’s Oxygen-Generating Experiment MOXIE Completes Mars MissionPrimary · checked Oct 6, 2026
14. NASA — NASA’s Perseverance Mars Rover Extracts First Oxygen from Red PlanetPrimary · checked Oct 6, 2026
15. NASA — NASA Finds Ancient Organic Material, Mysterious Methane on MarsPrimary · checked Oct 6, 2026
16. NASA JPL — First You See It, Then You Don’t: Scientists Closer to Explaining Mars Methane MysteryPrimary · checked Oct 6, 2026
17. ESA — First results from the ExoMars Trace Gas OrbiterPrimary · checked Oct 6, 2026
18. NASA JPL — NASA’s Curiosity Rover Captures Shining Clouds on MarsPrimary · checked Oct 6, 2026