We are on the cusp of a golden age of space travel in which, for the first time, it will be possible for large numbers of people to venture into space. Some intend to stay. But what happens—and will happen—to us in the extreme conditions of space? What should space tourists expect to happen to them during a journey to an orbiting space station, the Moon, or Mars? What would happen to children born on another planet? Would they evolve into a new species? 

This book focuses on the latest science, taking readers to the front lines of research. We hear from astronauts, including Scott Kelly who writes the foreword, and we join a team of scientists guiding a rover across the surface of Mars. We visit a high-security lab where engineers are simulating space radiation to measure its effects on the body. We travel to isolated islands where field biologists are gleaning insights into evolutionary processes applicable to people isolated on faraway planets. We meet synthetic biologists developing gene-editing tools to equip future humans to thrive in alien environments. We watch a rocket designed to carry humanity to Mars make its first successful launch. And then we ask, knowing what we know: Should we go?

In the excerpt below, Scott Solomon explores the conditions on Mars—and if we might be able to alter them to be more suitable to human life.

◊◊◊◊◊

The long-term goal for NASA’s Artemis mission is to send people to Mars. China has Martian ambitions, too, as do private companies like SpaceX. Given its distance and orbit, the shortest a mission to Mars could last would be about two and a half years. Some, like SpaceX CEO Elon Musk, envision much longer—perhaps even indefinite—stays. But what would that look like from a human perspective? Plans for how people could survive on Mars, whether for short-duration missions or extended stays, have evolved as our understanding of the conditions on the planet has changed.

Early visions of human habitats on Mars often featured large, clear domes built on the surface. In addition to promising amazing views, these attractive-looking domes could serve as greenhouses for crops and other plants—perhaps even recreating entire ecosystems. But the discovery that Mars has both a paper-thin atmosphere and no functional magnetosphere—and the confirmation that radiation levels at the surface are nearly as intense as in deep space—forced a search for habitat designs that would include much more substantial radiation shielding. The easiest and perhaps most effective way to provide shielding from radiation is using regolith, or Martian soil. It could be piled on top of a structure (so much for those amazing views from inside the dome) or the habitats could be built underground. Perhaps the easiest solution would be to create habitats inside lava tubes—natural tunnels that form as lava flows, created as the outer edges cool and solidify while the hot, molten interior flows until it runs out of material.

I have to admit, the idea of traveling all the way to Mars only to live underground strikes me as thoroughly depressing. For our entire evolutionary history, humans have not only lived on Earth, but have lived on its surface. That said, humans have used caves as homes and shelters since prehistoric times, and people even in more recent times have sometimes constructed underground homes. The most extensive example is a network of underground tunnels and chambers in Turkey that was used for at least the last two thousand years. The site, known as Derinkuyu, was discovered by accident in 1963 when a local man was renovating his home.23 A small hole he found in the wall turned out to be the opening to a tunnel—one of more than 600 entrances to what was once a vast underground community that housed as many as 20,000 people. It consisted of an astonishing eighteen levels, including rooms where livestock and food were kept. Its primary function was so that its inhabitants could hide and be protected from invaders. As such, it had to have its own water supply and to allow air to flow in and out. The inhabitants collected human waste in clay jars they could seal up when they got full, and there were designated areas within the subterranean network for burying their dead.

The description of Derinkuyu reminds me of another type of underground society—those made by ants. I spent years excavating the enormous nests of leafcutter ants for my doctoral thesis. Much like the ancient underground city in Turkey, leafcutter ants construct their nests using a system of tunnels and chambers. A single leafcutter ant nest can occupy some 2,300 square feet in area—the size of a house—and can be home to

more than 5 million ants. The ants cut pieces of leaves and carry them into their subterranean chambers where they cultivate fungi that can break down the leaves. The fungi are then harvested by the ants as their primary food source. Tunnels at the edge of the nest bring oxygen-rich air into the nest as the wind blows across it, and large openings at top of the nest release carbon dioxide as the ants and the fungi they grow all respire.

The discovery of the ancient Turkish city seems to suggest that people are able to live underground much like ants. Perhaps Martian habitats can be constructed using architectural designs modeled after ant nests. But there is an important difference to consider. Most ants don’t spend their entire lives underground. Worker ants leave the nest to find food, build and repair the nest, and defend it from enemies. Likewise, people who once used caves and other underground homes weren’t restricted to them—at least not permanently. Even if they lived underground, which wasn’t always the case, they went outside to find food, interact with people from other groups, and—I can’t help but imagine—just to get some fresh air and sunshine.

On Mars, going outside would be a lot more complicated. You would need a pressure suit with a life support system to manage your air supply and temperature. And you would expose yourself to high levels of radiation. Surface time would have to be limited.

Another possibility that has been suggested, both by science fiction authors and by scientists, is that we might be able to change the conditions on Mars enough to make it possible to live more comfortably on its surface. In his 1942 short story Collision Orbit, science fiction author Jack Williams coined the term “terraforming” to describe the process of transforming a planet to make it habitable. But the idea didn’t reach the mainstream scientific community until 1961, when astronomer Carl Sagan suggested, in an article in the journal Science, that Venus could potentially be transformed through a process of planetary engineering to prepare it for what he called “comfortable human habitation.” This could be accomplished, Sagan proposed, using algae that can survive in extreme conditions.

At the time, Venus was known to have a thick atmosphere made largely of carbon dioxide and high surface temperatures. Just how high was not known, but the Mariner 2 mission just a year later would reveal that it was practically an inferno—its surface temperatures

average 471 degrees Celsius. Its atmosphere was shown to be incredibly thick, with clouds of sulfuric acid extending up to fifty miles above its surface. The carbon dioxide acts as a greenhouse gas, trapping heat from the Sun near the planet’s surface and causing the planet to bake.

Mars has the opposite problem. With such a thin atmosphere, very little heat is trapped. With Venus looking like a literal hellscape, it didn’t take long to apply the idea of terraforming to Mars. After all, we’ve inadvertently caused our own planet to warm by increasing the amount of carbon dioxide and other greenhouse gasses in the atmosphere. Couldn’t we do the same to Mars—deliberately—and make it warmer and more hospitable?

The idea was tempting. After all, it appears that Mars did once have a more Earth-like environment, with mild temperatures and flowing water. Its atmosphere already contains a lot of carbon dioxide, with more thought to be frozen at the poles in the winter in the form of dry ice.

To get a better handle on how feasible terraforming might be, I called planetary scientist Jim Kasting at Penn State University, a member of the National Academy of Sciences and an expert on planetary habitability. “I’m a bit of a pessimist—quite a pessimist—on terraforming the whole planet,” he told me. “I think it’s infeasible . . . I actually don’t understand why people are so fixated on terraforming Mars. I think it’s because they don’t understand how difficult it is,” he said.

Kasting walked me through the challenges of increasing Mars’s atmospheric pressure and temperature, citing the proposals for nuclear weapons and manufacturing potent greenhouse gasses. He didn’t think these were realistic. But then he brought up another challenge I had not yet heard.

“There’s another problem that we haven’t talked about that may be the hardest one of all, and that’s nitrogen. Mars has a teeny amount of nitrogen in its atmosphere,” he said.

Here on Earth, the air we breathe contains 78 percent nitrogen—it’s the single greatest component of our atmosphere. By contrast, Mars’s atmosphere has only about 3 percent nitrogen. Kasting explained that nitrogen is important to have in the atmosphere because it balances out the oxygen we need to breathe without being harmful or dangerous.

“You don’t want a pure oxygen atmosphere,” he observed. “Pure oxygen atmospheres are very flammable. We learned about that in the Apollo 1 disaster. There was a spark in the capsule and then the whole thing quickly caught fire and burned them up before they could get out. After that, we learned that you have to mix oxygen with another gas, like nitrogen . . . you need about twice as much nitrogen as you have oxygen.”

While other gasses, like carbon dioxide or argon, could serve the same function as nitrogen, each of those has its problems. Our bodies cannot tolerate high levels of carbon dioxide. And argon is extremely rare—making up only 1.6 percent of Mars’s atmosphere, so it’s unlikely there would be enough to buffer the oxygen in a terraformed Mars.

Kasting brought up the idea of bombarding Mars with an asteroid, perhaps one that contains a lot of nitrogen. Most likely it would require many asteroid collisions to supply enough material. In theory, that could work, he thought. “But you’d have trouble keeping it because it gets swept away,” he noted. “Mars doesn’t have an intrinsic magnetic field today. Its ionosphere interacts directly with the solar wind. That’s why it doesn’t have any nitrogen—because it lost it by these non- thermal escape processes which would continue to act even as you were trying to terraform it. You’re fighting Mother Nature the whole time,” he said.

In other words, any nitrogen you put into Mars’ atmosphere would not stay there; the nitrogen would be lost to space as the atmosphere gets stripped away by the stream of solar particles that constantly bombards the planet. This struck me as very bad news for the prospect of terraforming.

“That’s not unique to nitrogen, right?” I asked. “Wouldn’t that be true of any other gas that was added to Mars’s atmosphere, including oxygen?”

“Yes. Everything gets stripped,” Kasting said.

So even if we could make Mars’s atmosphere thicker, increasing its pressure and heating it to the point where it was a place where we could live, the change would be temporary. Eventually, the solar wind would cause Mars’s atmosphere to gradually thin, returning it closer to its current uninhabitable state. Terraforming would be an uphill battle, one that would require continual maintenance.

One way that maintenance could be done, Kasting offered, would be to regularly strike Mars with asteroids to replenish the elements in the atmosphere, like nitrogen and water, that were lost to space. But then again, once people are living on Mars, the idea of intentionally blasting it with a massive asteroid would probably be counterproductive.

“The people living there probably wouldn’t want to have a several-kilometer-diameter asteroid aimed at them,” he mused.

It’s a sobering irony. One of the primary motivations for settling Mars is to help protect us from the possibility of extinction caused by a disaster on Earth, like an asteroid impact. And yet asteroid impacts might be needed to keep Mars habitable—but they would likely be catastrophic to anyone living on it.

Kasting thinks the science fiction visions of a fully terraformed Mars—in which people can walk around on its surface without pressure suits, and breathe the air the way we do on Earth—is not really feasible. It certainly couldn’t be done with our existing technology. Still, Kasting acknowledged that the development of future technologies might change that.

“Everything that I think is difficult might not look so difficult 200 years from now,” he offered.

But Kasting pointed out that there are different degrees of terraforming. He admits that a more modest version of terraforming, in which Mars has a thicker atmosphere made mostly of carbon dioxide, might eventually be feasible. With enough carbon dioxide it might be possible to warm the planet to a point where water could flow on its surface. People wouldn’t be able to breathe without an oxygen tank and a mask, but they could at least walk around on the surface without a pressure suit. And some plants could be grown on the surface without requiring a pressurized greenhouse—assuming the toxic perchlorates in the soil could be removed. The planet would look much more Earthlike, with lakes and rivers surrounded by green hills and valleys.

Another benefit of the denser atmosphere would be some additional radiation shielding, contributing to the habitability of the surface. Without a magnetosphere, there would still be higher radiation exposures than we experience on Earth. And people would still need to live inside habitats with breathable air and some radiation shielding, but the outside environment would not be nearly as hostile.

This vision for the future of Mars seems much more inviting and pleasant than living in sealed containers below ground, as would be necessary without any terraforming. It’s a place that would be more likely to appeal to a wide range of people, not only those already eager to live out their days on the wild galactic frontier.

Adapted from Becoming Martian, published by the MIT Press. Copyright © 2026 Scott Solomon. All rights reserved.

About the Author

Scott Solomon is Teaching Professor of Biosciences at Rice University in Houston. He is also a Research Associate at the Smithsonian Institution’s National Museum of Natural History. His first book, Future Humans, was named a 2017 Best Book by the American Association for the Advancement of Science (AAAS). He is also the host of the podcast Wild World with Scott Solomon and cowriter and coproducer of the series Becoming Martian.