What Is Mars's Atmosphere Like?
QUICK ANSWER
Mars's atmosphere is about 1 percent the density of Earth's and made of roughly 95 percent carbon dioxide, with traces of nitrogen, argon, and other gases. It's too thin to breathe, too thin to block harmful radiation, and too thin to retain much heat, but thick enough to support planet-wide dust storms.
Mars's atmosphere is the planet's most dramatic limitation. It's thin enough that water boils almost instantly on the surface, but thick enough that planet-wide dust storms can darken the sky for months. It's the worst of both worlds: too thick to ignore, too thin to do you any good.
What is Mars's atmosphere made of?
According to NASA, Mars's atmosphere is about 95.3 percent carbon dioxide, 2.7 percent nitrogen, 1.6 percent argon, and trace amounts of oxygen, carbon monoxide, water vapor, and other gases. There's only about 0.13 percent oxygen, vastly less than the 21 percent in Earth's air. The composition is similar to Venus's atmosphere (also mostly CO2), but at vastly lower density. Mars has roughly 1 percent of Earth's atmospheric pressure at the surface.
Can you breathe on Mars?
Not at all. The atmosphere is too thin and contains essentially no oxygen. Even if you ignored the temperature and radiation problems, an unprotected human on Mars would suffocate in minutes. Worse, the thin atmosphere means that without a pressure suit, water in your body would start boiling at body temperature, a condition called ebullism. Any human on Mars needs a fully sealed environment, either a pressurized suit or a habitat, just to keep breathing and stay intact.
Why is Mars's atmosphere so thin?
Because Mars lost most of it over billions of years. Solar wind, the stream of charged particles from the Sun, has been slowly stripping away Mars's atmosphere because Mars no longer has a strong global magnetic field to deflect the wind. Mars's lower gravity also makes it harder to hold onto atmospheric gases, especially lighter ones. The result is a planet that once had a much thicker atmosphere (possibly thick enough to support liquid water) but has been steadily losing it for over 3 billion years.
What is weather like on Mars?
Cold, dry, and dusty. Mars has seasons (about twice as long as Earth's because Mars's year is longer), but no rain or snow in the Earth sense. What it does have is dust storms, sometimes massive: about every few years, a regional storm can grow until it covers the entire planet in dust, blocking sunlight for weeks or months. Mars also has dust devils, including some that are taller than skyscrapers, and rare thin clouds of water ice high in the atmosphere.
Mars's atmosphere is thin, toxic to breathe, and unable to retain heat or block radiation, but it's still active enough to drive dust storms that can swallow the entire planet. It's the kind of atmosphere that doesn't help you and won't get out of your way. Any human presence on Mars has to work around it.
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