Mars's Atmosphere — Thin Air, Big Storms
Mars has air. You just couldn't breathe a single second of it.
Earth's atmosphere is the reason we exist. It's full of oxygen, traps the right amount of heat, blocks dangerous radiation, and lets liquid water sit on the surface without boiling away. Mars's atmosphere is doing none of those jobs.
It's there, technically — there's a thin layer of air around Mars. But it's freezing, unbreathable, and so thin that it's barely worth calling air. Here's why.
What Is Mars's Atmosphere Made Of?
The breakdown is brutal:
- 95% carbon dioxide (CO₂)
- 2.7% nitrogen
- 1.6% argon
- 0.16% oxygen
- Tiny traces of carbon monoxide, water vapor, and other gases
Compare that to Earth, where 21% of the air is oxygen and only 0.04% is carbon dioxide. Mars's atmosphere is, in effect, a planet-wide cloud of the gas you breathe out, with almost none of the gas you breathe in.
Even if you could somehow handle the lack of oxygen, there's a second problem.
The Atmosphere Is Almost Not There
Mars's atmosphere is incredibly thin. The pressure at the surface is around 610 pascals. Earth's surface pressure is about 101,000 pascals. Mars's atmosphere has less than 1% of the pressure of Earth's.
That's not just an inconvenience. At pressures that low, water boils at room temperature. Worse, if a person stood on Mars without a sealed spacesuit, the gases dissolved in their blood would start coming out of solution — basically, the blood would bubble. There's a name for what would happen: ebullism. It would be very bad, very fast.
So the atmosphere on Mars is officially the same kind of "atmosphere" you'd find in low Earth orbit. Astronauts visiting Mars would need spacesuits whenever they stepped outside, exactly the same as they need on the Moon.
Why Is the Air So Thin?
Mars used to have a much thicker atmosphere. About four billion years ago, scientists believe, Mars's air was probably dense enough to support liquid water on the surface and may have had clouds and rain.
Then Mars lost it.
The trouble started when Mars's magnetic field faded away. Earth still has a strong magnetic field, generated by the spinning iron in our planet's core. That field acts like an invisible shield, deflecting most of the charged particles streaming out of the Sun (the solar wind) before they can reach our atmosphere.
Mars's core cooled down faster than Earth's. The magnetic field weakened, and the solar wind slammed into Mars's upper atmosphere unprotected. Particle by particle, the Sun stripped Mars's air away into space.
This isn't ancient history, either. NASA's MAVEN spacecraft has been measuring it since 2014. Mars is still losing about 100 grams of atmosphere every second to the solar wind. That's slow, but over billions of years it adds up.
Why Mars Is So Cold
Mars's average surface temperature is about –63 °C (–81 °F). On a sunny summer day at the equator, it can climb to a chilly 20 °C (70 °F). On a winter night near the poles, it crashes down to –153 °C (–225 °F).
Two things make Mars so cold. Mars is farther from the Sun than Earth, so it gets less than half as much sunlight in the first place. But the bigger reason is the atmosphere. Earth's thick atmosphere acts like a blanket — it traps some of the heat the surface picks up during the day and slowly releases it through the night, keeping things warm. Mars's atmosphere is too thin to do that. Whatever heat the surface absorbs in daylight gets radiated straight back out into space the moment the Sun goes down.
That's why temperatures on Mars swing so dramatically between day and night. There just isn't enough air to hold the warmth in.
The Famous Dust Storms
Mars has the largest dust storms anywhere in the solar system. And they get huge.
Most of the time, dust storms on Mars are local — just a few kilometers across. But every few Mars years, one of them grows. And keeps growing. The biggest storms can swell until they cover the entire planet for months at a time. From Earth, telescopes see Mars go from clearly-visible-features to one fuzzy orange ball.
The most famous recent example was a global dust storm in 2018 that ended the Opportunity rover. Opportunity ran on solar panels, and when the storm blocked sunlight from reaching the surface for months, the rover ran out of power and never woke up again.
Why do dust storms get so big on Mars? A few reasons:
- Mars's dust is extremely fine — finer than flour. Once it's airborne, it stays up for weeks.
- The thin atmosphere actually helps. It's hard to start a dust storm in thin air, but once one gets going, there's no rain to wash the dust back out.
- The Sun heats the dust, and the warmed dust heats the air around it, which causes more wind, which lifts more dust. The whole thing snowballs.
Dust Devils
Smaller cousins of the big storms are dust devils. They work just like the dust devils you sometimes see in a dry parking lot on Earth — a column of warm air rising fast off the surface, spinning, and sucking up dust.
Martian dust devils are bigger and more impressive than ours. Some can grow several kilometers tall. NASA's rovers have caught them on camera many times, weaving across the plains like tornadoes. The Curiosity and Perseverance rovers also use dust devils as their personal cleaning service — they sometimes blow accumulated dust right off the rovers' solar panels.
Wind, Frost and Clouds
Mars actually has weather, just very weak weather.
Wind speeds usually run between 2 and 30 km/h. They can spike higher in storms, but the air is so thin that even a 100 km/h wind on Mars would feel more like a gentle breeze on Earth. The famous scene in the movie The Martian where a windstorm tears apart a Mars base — that part isn't realistic. Real Mars wind couldn't damage a tent on Earth.
There's also frost. On cold mornings, you can see thin layers of carbon-dioxide frost (essentially dry ice) on rocks and the ground. Wisps of high-altitude clouds, made of water ice and dry-ice crystals, drift across the sky most days. Sometimes they catch the sunset light and glow with strange colors.
Wow stat: Mars's atmosphere is so thin that the temperature at your feet on a sunny day might be 20 °C, but the temperature at your head — just two meters higher — could be close to freezing. Air that thin is terrible at carrying heat upward.
Could the Atmosphere Be Restored?
This is one of the big terraforming questions. Scientists have proposed all kinds of ideas for thickening Mars's air: melting the polar dry-ice caps to release CO₂, smashing comets full of ice into the surface, or even building giant orbital mirrors to warm the planet up.
The trouble is the same one Mars had originally. Without a magnetic field to protect a new atmosphere, the solar wind would just strip it away again. Some scientists have suggested putting a giant magnetic shield in space between Mars and the Sun to block the solar wind, but that's currently far beyond our technology.
For the foreseeable future, Mars stays cold, dry, and thin. Astronauts who go there will need to bring their air with them.
Frequently Asked Questions
What is Mars's atmosphere made of?
Mars's atmosphere is 95% carbon dioxide, 2.7% nitrogen, 1.6% argon, and only 0.16% oxygen, with tiny traces of other gases. That's almost the opposite of Earth's atmosphere, which is 21% oxygen and only 0.04% carbon dioxide.
Can you breathe on Mars?
No. There's almost no oxygen in Mars's atmosphere — only 0.16%, compared to 21% on Earth. The pressure is also too low for human lungs to work properly. Anyone on Mars without a sealed spacesuit would lose consciousness within seconds.
Why is Mars so cold?
Two reasons. Mars is much farther from the Sun than Earth, so it gets less than half as much sunlight. And Mars's atmosphere is too thin to trap heat, so whatever warmth the surface picks up during the day escapes straight back into space at night.
How big are dust storms on Mars?
Mars has the biggest dust storms in the solar system. Most are small and local, but every few years a storm grows until it covers the entire planet, sometimes for months at a time. The 2018 global dust storm ended NASA's Opportunity rover.
Why is Mars's atmosphere so thin?
Mars used to have a much thicker atmosphere about four billion years ago. Then Mars lost its magnetic field, which left the upper atmosphere unprotected from the Sun's solar wind. The solar wind slowly stripped most of Mars's air away into space, and it's still happening today, very slowly.