How Would Humans Protect Themselves On Mars?

To survive on Mars, humans would shelter inside pressurized habitats shielded from radiation by thick water ice, piled-up soil (regolith), or underground lava tubes. Going outside means a pressurized spacesuit and a portable oxygen supply, since the thin air is roughly 95% carbon dioxide. Breathable oxygen and even rocket fuel can be produced on-site from local ice and the atmosphere, as NASA's MOXIE experiment proved. Outside the shelter, Curiosity’s RAD instrument measured about 0.67 millisieverts of radiation per day, so a full expedition adds up to roughly 1 sievert, above NASA’s 600-millisievert career limit, and the surface pressure is so low that an unprotected person’s body fluids would boil.

This might sound a bit depressing, but things aren’t going particularly well here on Earth. Despite huge advances in technology and collective intelligence around the world, there are major issues facing this planet that often seem insurmountable. Between climate change, rising political and social tension, and a population that keeps climbing, some people can’t help but look for ways to escape.

For those people who are truly fed up with life on Earth, they are even looking towards the stars, or at least the nearest planet that could support life – Mars. The idea of colonizing and surviving on Mars has been thrown around a lot in recent years and decades, but there are some serious obstacles – such as freezing temperatures, a lack of oxygen, and extreme cosmic radiation. With all that standing in the way, many people are asking… how would human beings possibly protect themselves in the harsh Martian landscape?

Short Answer: Possible solutions include ice-insulated igloos, soil-covered or lava-tube shelters for radiation shielding, robot construction crews and making oxygen on-site.

Setting Up Camp

We have already managed to send rovers and unmanned missions to Mars, so we are confident in our ability to make the trip, but once potential colonists or researchers arrive, there needs to be somewhere they can be protected from the harsh environment of Mars. Remember, the average temperature on Mars is roughly -60 °C (-80 °F), as compared to an average of about 15 °C (59 °F) on Earth, and Martian nights can plunge well below -100 °C (-148 °F).

To make “base camp” on Mars, it is suggested that robots would first be sent to Mars to construct the necessary habitat, as they can function and survive in the unforgiving conditions of the planet. These robots could also be tasked with extracting resources from the Martian surface, decontaminating them, and essentially stockpiling the things future colonists would need. Growing food would be essential for long-term colonization, but the Martian soil is laced with perchlorates, toxic salts found across the planet at concentrations around 0.5%. In humans, perchlorate blocks the thyroid from taking up iodine, and it is harmful to plants too, so the soil would have to be rinsed or chemically treated before anything could be grown in it. Robots could begin that leaching process and set the stage for agricultural efforts, just like many of you saw in The Martian!

With those supplies in place, it would be a relatively easy transition for colonists to arrive and begin to operate a colony or base immediately. The atmospheric issues can be countered by current technology, such as spacesuits, like those currently used by astronauts, which can provide the necessary oxygen. The atmosphere on Mars is less than 1% the density it is on Earth, and roughly 95% of that thin “air” is carbon dioxide, which is unbreathable for humans. Worse still, Mars lost its global magnetic field billions of years ago, and its feeble atmosphere stops almost none of the radiation pouring in from space. That means a steady drizzle of high-energy galactic cosmic rays, punctuated by sudden bursts of solar particles, a dose that settlers couldn’t survive out in the open for long, which brings us to the real crux of the “living on Mars” problem – the shelter.

What Does Home Look Like?

In 2016, an old architectural concept was dusted off and brought back into the light – the igloo. Called the Mars Ice Home, this high-tech igloo will basically be a transparent bubble, with large storage pockets on the edges to hold water and carbon dioxide. The water will turn into ice, due to the freezing temperature of Mars, and that’s where the beauty of this plan lies.

This fancy igloo serves a number of purposes; first of all, the translucent nature of ice means that Martian settlers will be able to get natural light, an impossibility in the other proposed ideas (where astronauts live underground to protect from radiation). More importantly, however, ice (and the liquid water it is made from) is one of the best materials we have for blocking cosmic radiation, which on Mars arrives mainly as fast-moving charged particles, chiefly protons and heavier atomic nuclei, rather than as light.

For those of you who paid attention in chemistry class, you know that H₂O is composed of 2 hydrogen atoms and 1 oxygen atom. That hydrogen is exactly what makes water such a good radiation shield. Because a hydrogen nucleus is a single proton with almost the same mass as the incoming cosmic-ray particles, collisions with it sap their energy efficiently while producing fewer dangerous secondary particles than dense materials like metal would, keeping those inside far safer from the radiation.

This igloo/icy inner tube structure could be extended to other structures, making the “colony” larger, an interconnected network of radiation-free pods and living spaces, where artificial atmosphere could eventually be generated, meaning that colonists could actually live without a spacesuit!

The ice home is not the only plan on the table. Two other approaches lead the field, and both lean on the same idea of putting mass between people and the sky. The simplest is to bulldoze loose Martian soil over a habitat: studies suggest a layer of regolith roughly 1 to 1.6 meters (about 3 to 5 feet) thick would cut a settler’s yearly radiation dose to a tolerable level. The other is to move in for free, using Mars’ natural lava tubes, large hollow tunnels left behind by ancient volcanoes. A few meters of rock overhead shields against cosmic rays, solar flares, micrometeorites, and the wild day-to-night temperature swings all at once, which is why these underground caverns are among the most promising real estate on the planet.

How Much Radiation Would Settlers Actually Get?

We have been throwing the word “radiation” around rather freely, so let’s put some numbers on it. When NASA’s Curiosity rover flew to Mars, it carried an instrument called the Radiation Assessment Detector (RAD), and RAD kept counting after the rover landed in Gale Crater. Sitting on the Martian surface, it measured an average galactic cosmic ray dose of about 0.67 millisieverts per day; tucked inside the spacecraft on the way there, the figure was roughly 1.8 millisieverts per day. For scale, the U.S. Environmental Protection Agency puts the average American’s dose from all sources, medical scans included, at about 6.2 millisieverts per year. A settler on Mars would collect that in about nine days.

Add it up over a realistic expedition (180 days out, 500 days on the surface and 180 days home) and the Curiosity team’s estimate comes to about 1 sievert, or 1,000 millisieverts, with each of the three legs contributing roughly equally. That matters because NASA’s career limit for its astronauts, written into the NASA-STD-3001 standard, is 600 millisieverts, the same for every age and both sexes, and set to keep an astronaut’s added lifetime risk of dying from cancer below 3 percent. A National Academies review of that standard put a 1,000-day Mars mission at about 1.07 sieverts, roughly 1.8 times the limit. In other words, with today’s shielding, a Mars crew would need a formal waiver just to be cleared for launch.

The two flavors of space radiation call for different defenses. Solar particle events are bursts of mostly low-energy protons, and NASA’s engineers say almost all of them can be physically blocked; the standard fix is a “storm shelter” inside the habitat with an extra 10 centimeters (4 inches) of water-equivalent shielding around the crew quarters, which can be improvised by stacking water containers and other hydrogen-rich supplies (a 1-in-1,000-year storm would call for about 20 cm, or 8 inches). Galactic cosmic rays are the harder problem. These fast, heavy nuclei shatter the atoms they hit and scatter into showers of secondary particles, which is why simply bolting on more metal helps far less than you would hope. That is also why hydrogen keeps coming up in NASA’s shielding studies: because a hydrogen nucleus is about the same size as an incoming proton or neutron, water and polyethylene plastic stop particles efficiently without much of that splash-back, and it is why the ice home and the meter or more of soil described above are engineering, not whimsy.

What Would Happen If You Stepped Outside Without A Suit?

Every plan above assumes the pressure hull holds. So what if it doesn’t, or a settler simply cracks the airlock without suiting up? Surprisingly, the cold is not what gets you first. The killer is pressure. Mars’ surface pressure is less than 1 percent of Earth’s, which puts it well below what aerospace doctors call the Armstrong line: at 47 millimeters of mercury (about 6.3 kilopascals, or 0.9 psi), a pressure Earth’s atmosphere reaches at roughly 19,200 meters (63,000 feet) up, water boils at normal body temperature, 37 °C (98.6 °F). Below that, the water in your tissues starts to vaporize and the gases inside you expand, a condition NASA’s medical planners call ebullism. Their own planning documents describe the result as injury to multiple organs, note that the lack of oxygen causes loss of consciousness in about 9 to 11 seconds, and classify a habitat that loses its pressure as “catastrophic and not likely survivable.” (For the gorier details, we have covered what a vacuum does to the human body elsewhere.)

That is why the spacesuit is non-negotiable, and why it is best thought of as a wearable spacecraft. The suits used for spacewalks outside the International Space Station are pressurized to 4.3 psi (29.6 kPa), and their backpack life-support system is rated for about 8 hours of work, with a 30-minute emergency oxygen reserve. So the honest answer to “how long could you live on Mars in a spacesuit?” is roughly one working day per charge, after which you had better be back inside a habitat that can refill it. Our article on how long an astronaut can survive in a spacesuit walks through the same arithmetic.

Gravity is the subtler hazard, because it never announces itself. Mars pulls with only about 38 percent of Earth’s gravity, and while no one has lived in that for long, we know what near-weightlessness does: astronauts on the ISS lose roughly 1 percent of the density in their weight-bearing bones for every month in orbit if they don’t take precautions, which is why station crews exercise for about two hours a day. NASA openly flags that a crew arriving on Mars may have to do strenuous work in partial gravity right after months of that deconditioning. A Martian settlement, then, needs a gym as badly as it needs a storm shelter, and how the human body fares over years at 0.38 g is a question no one has yet been able to test.

Why Is Mars So Cold And Airless In The First Place?

It is fair to ask why we should have to go to all this trouble. Mars did not start out this way. Dry riverbeds and water-formed minerals show that billions of years ago the planet was warm and wet, with liquid water flowing across its surface, and that takes a far thicker blanket of air than the wisp Mars has today. Two things went wrong, and they are connected. First, the planet’s internal dynamo, the engine in its core that once generated a global magnetic field, switched off. Its fossil imprint survives as strongly magnetized patches of crust in the southern hemisphere, and magnetic data from NASA’s MAVEN orbiter indicate that the dynamo was still running around 4.5 billion and again around 3.7 billion years ago. Today there is no global field at all. Second, without that magnetic shield to deflect charged particles from the Sun, the solar wind went to work on the atmosphere.

MAVEN, which has been circling Mars since 2014, measured just how thorough that work has been. By comparing two isotopes of argon in the upper atmosphere (the lighter one escapes more easily, so the gas left behind is enriched in the heavier one), the MAVEN team calculated that about 65 percent of all the argon Mars ever had has been lost to space. The mechanism is called sputtering: ions picked up by the solar wind slam into the upper atmosphere at high speed and physically knock gas out into space. Argon is a noble gas that cannot be locked away in rocks, which makes it a clean tracer, and the same process removed the majority of the planet’s carbon dioxide as well. Most of this happened early on, when the young Sun poured out far more ultraviolet light and a fiercer solar wind than it does now. (Where the water went is a story of its own.)

The cold follows directly from the missing air. Mars orbits about 1.5 times farther from the Sun than Earth does, so it receives less sunlight to begin with, but the bigger problem is that its thin atmosphere cannot hold onto the warmth it does get; as NASA puts it, heat from the Sun easily escapes the planet. The result is a world where the surface can reach 20 °C (70 °F) at its very warmest but drop to about -153 °C (-225 °F) at its coldest, and where, standing on the equator at noon, it would feel like spring at your feet (24 °C, 75 °F) and winter at your head (0 °C, 32 °F). For settlers, this back story is the whole point. The radiation, the near-vacuum and the deep cold all trace back to the same story, a magnetic field that switched off and an atmosphere the solar wind has been stripping ever since, and restarting a planet’s core is not on anyone’s to-do list. Whether we could ever thicken the atmosphere again is a separate question; for now, the only option is to bring the shelter with us, or dig it.

How Close Are We To Living On Mars?

While the prospect of living on another planet is becoming more attractive by the day, there are still quite a few hurdles before we reach the Red Planet. From Barack Obama to Elon Musk, a lot of projections have recently been made about when and how we are going to colonize Mars, but some people remain skeptical.

First of all, a crewed mission is a marathon. With today’s rockets the journey is roughly six to nine months each way, and because Earth and Mars only line up favorably about every 26 months, a crew would have to wait out more than a year on the surface before the return window opened, making the whole expedition close to three years door to door. That means hauling years of supplies and giving people room to live comfortably during long-term space journeys. It means building bigger spacecraft, which in turn means building more powerful rockets. SpaceX, Blue Origin, Lockheed Martin and NASA are some of the leading names in these efforts, and SpaceX is developing its giant, fully reusable Starship vehicle (the kind of rocket that could one day even launch satellites and spacecraft from the Martian surface) with Mars settlement as its stated long-term goal. Timelines keep slipping, though: in early 2026 SpaceX pushed its first uncrewed Starship flights to Mars back by several years to concentrate on the Moon, so a crewed landing is now widely expected no earlier than the 2030s. So far, every craft to reach the surface has been robotic, not human.

We often think about the ISS as being in outer space, but in truth, it orbits in low-Earth orbit, where Earth’s magnetic field (the same field that shapes the Van Allen radiation belts) still deflects much of the incoming cosmic radiation. On a long journey through deep space, far beyond that magnetic umbrella, additional consideration will need to be taken to protect travelers from the much higher levels of radiation pummeling the spacecraft during the trip. Safely landing on the surface of Mars using supersonic retropropulsion is also a tricky prospect, but one that SpaceX and other companies are working on with their reusable rockets and spacecraft.

There has been real progress on living off the land, too. On April 20, 2021, a toaster-sized instrument on NASA’s Perseverance rover called MOXIE (the Mars Oxygen In-Situ Resource Utilization Experiment) became the first device to make breathable oxygen on another planet, splitting it out of the carbon dioxide in the Martian air. By the time it wrapped up in 2023, MOXIE had run 16 times and produced about 122 grams (4.3 ounces) of oxygen in total. The amounts are tiny, but the proof of concept is huge: future crews may be able to manufacture both the air they breathe and the oxidizer for their return-trip rocket fuel right there on Mars, rather than dragging it all from Earth. Perseverance, meanwhile, keeps caching rock samples for an eventual return to Earth, and its companion helicopter, Ingenuity, flew 72 times before retiring in January 2024.

As you can see, there are numerous obstacles that still exist to this dream of a Martian colony, but with a global interest in this newest space race, it’s only a matter of time before we solve these problems and take our next tiny steps into the unknown!