What is Mars like? Could humans ever live there?

Mars is a cold, dry, rocky planet about half Earth's width, with a thin carbon-dioxide atmosphere, red iron-rich dust, and the largest volcano in the solar system. Standing on it would be like standing in a frozen desert with almost no air: it averages about −59°C, the air is too thin to breathe or to stop radiation, and gravity is a little over a third of Earth's. It once had rivers and lakes.

In short

• Mars is a frozen desert: thin carbon-dioxide air, an average temperature far below freezing, and dust storms that can cover the whole planet.
• Dry riverbeds, lake deltas and buried ice show that liquid water once flowed there, which is why rovers search it for signs of past life.
• People could visit with enough shielding and supplies, but radiation, low gravity and distance make living there far harder than any place on Earth.

What would you see and feel on Mars?

You would see a rust-colored desert under a pale, butterscotch sky. The color comes from iron oxide, rust, in the dust and rocks. On a clear day you might see one of its two small moons, Phobos or Deimos, lumpy rocks about 22 and 12 kilometers across.

The air would kill you in seconds without a suit, and not only because it lacks oxygen. According to NASA's Mars fact sheet, the atmosphere is about 95% carbon dioxide, and its average surface pressure is about 6 millibars, roughly 0.6% of Earth's. At that pressure, water in your body would start to boil at body temperature. Temperatures run from about 20°C at the equator on a summer afternoon to about −153°C at the poles.

Gravity is 38% of Earth's, so a person who weighs 80 kilograms on Earth would feel like 30. A day, called a sol, lasts 24 hours and 40 minutes, and a year lasts 687 Earth days.

	Earth	Mars
Width	12,756 km	about 6,792 km (53% of Earth's)
Gravity	1 g	0.38 g
Air pressure at the surface	about 1,013 millibars	about 6 millibars
Main gas in the air	nitrogen (78%)	carbon dioxide (95%)
Average temperature	about 15°C	about −59°C
Length of day	24 hours	24 hours 40 minutes
Length of year	365 days	687 Earth days

Why is Mars so extreme?

Mars is small, and small planets lose heat and air faster. Its core cooled, its global magnetic field faded billions of years ago, and without that shield the solar wind, the stream of charged particles from the Sun, stripped much of the atmosphere away. Thin air holds little heat, so Mars is cold, and it is farther from the Sun than Earth, about 228 million kilometers on average.

The landscape is built on a giant scale. Olympus Mons is the largest volcano known in the solar system, more than twice the height of Mount Everest, with a base about the size of the state of Arizona. Valles Marineris, a system of canyons, runs about 3,870 kilometers, nearly the width of the contiguous United States, and is up to 9 kilometers deep. Dust storms can grow until they cover much of the planet, and the dust can take months to settle, which is how a 2018 storm ended the solar-powered Opportunity rover.

Did Mars ever have water?

Yes. Mars was once wet enough for rivers, lakes and possibly a shallow sea. Orbiters and rovers have found dried river channels, fan-shaped deltas, and minerals such as clays that form only in water. Most of that water is gone now, lost to space or locked up as ice. Water ice lies just under the surface near the poles and in the polar caps.

That past is why rovers go where they go. NASA's Perseverance rover landed on 18 February 2021 in Jezero crater, which held a lake more than 3.5 billion years ago. In September 2025, a peer-reviewed paper in Nature reported that a rock sample it drilled, from a rock nicknamed Cheyava Falls, holds potential biosignatures: chemical and mineral patterns that life can leave behind. Potential is the key word. Processes without life can make similar patterns, and settling the question would need the samples studied in labs on Earth, a return mission whose future was uncertain in 2026.

Could humans live on Mars?

Visiting is possible in principle. Living there is a much harder problem, for four reasons.

The first is radiation. Earth's magnetic field and thick air block most cosmic rays and solar particles. Mars has neither, and the trip there crosses open space. The second is gravity: nobody knows what 0.38 g does to bones, muscles, eyes and hearts over years, or to a pregnancy, because no one has ever lived in it. The third is distance. Radio signals take between about 3 and 22 minutes each way depending on where the two planets are, so there's no real-time help from Earth, and the shortest practical launch windows come only every 26 months. The fourth is supplies: air, water, food and fuel all have to be brought, or made from local ice and carbon dioxide with equipment that has never been run at scale there.

Worked example: the radiation bill for one trip

Curiosity's radiation detector measured the doses directly. According to the Southwest Research Institute's 2013 report of its results, the dose inside the spacecraft on the way to Mars was about 1.8 millisieverts (mSv) a day, and the dose on the surface averaged about 0.67 mSv a day. A sievert measures radiation's effect on the body.

Take a mission of 180 days out, 500 days on the surface and 180 days back:

• Travel: 360 days × 1.8 mSv = 648 mSv.
• Surface: 500 days × 0.67 mSv = 335 mSv.
• Total: about 983 mSv, close to 1 sievert.

The researchers linked a dose of 1 sievert to about a 5% higher risk of dying of cancer. NASA's career limit for its astronauts, set in 2022, is 600 mSv, so one such mission would exceed a whole career's allowance. Shorter trips, shielding with water or soil, and timing launches to the solar cycle can lower the number, but not to zero.

Still argued

When, and whether, people will settle Mars is argued rather than known. Space agencies and companies, SpaceX most prominently, have announced crewed Mars plans, and their target dates have repeatedly slipped; no crewed mission had flown as of November 2026. Supporters say a settlement would make humanity less vulnerable to disasters on one planet. Critics, including some planetary scientists, say the radiation, gravity and cost problems are unsolved, and that robots explore Mars far more cheaply.

How does Mars compare to its neighbors?

Mars is one of the four rocky planets of the solar system, along with Mercury, Venus and Earth. Venus went the other way: it kept a thick carbon-dioxide atmosphere, and a runaway greenhouse made it the hottest planet. Earth sits between the two extremes, which is part of why it alone has liquid water on its surface today.

People who have lived longest away from Earth did it on the International Space Station, 400 kilometers up, where help is hours away rather than months. And if Mars once had life and it died out, or never started, that bears on the Fermi paradox: how common life is across the universe.

Check yourself

• Without looking back: why does a small planet like Mars end up with thin air and a cold surface?
• What is the evidence that Mars once had liquid water, and why does it matter for the search for life?
• Name the four main obstacles to living on Mars, and say which one the radiation numbers above make clearest.

Sources

• Mars fact sheet — NASA Goddard Space Flight Center
• Mars facts — NASA Science
• Mars 2020 Perseverance rover — NASA Science
• SwRI scientists publish first radiation measurements from the surface of Mars — Southwest Research Institute, 2013
• Radiation protection technical brief — NASA Office of the Chief Health and Medical Officer, 2023