One day, Mars might become a home to humans. But first, there’s the cinematic, sci-fi challenge of making the Red Planet suitable for life. There’s a problem, though: The typical person can’t get to space safely. That throws a wrench into the whole “let’s move to Mars” plan in the face of extreme climate change and other existential risks on Earth.

Today, the path to becoming an astronaut is “littered with the hopes and dreams of medically disqualified candidates,” said Shawna Pandya, a research astronaut with the International Institute for Astronautical Sciences (IIAS) and the director of its Space Medicine Group. “Once upon a time, kids being diagnosed with Type 1 diabetes in the doctor’s office would be told, ‘Well, you could still be anything, except an astronaut.’”

Have space aspirations?

Here are some of the common reasons why you might be medically disqualified from becoming an astronaut:

• Tobacco use
• Autoimmune disorders
• Temporomandibular joint (TMJ) disorders
• Sleep apnea
• Asthma
• Hypertension
• Migraines
• Anxiety and depression

Astronauts inherently aren’t representative of the broader population — they’re selected for being in very good health. The stress of existing in essentially weightless microgravity conditions, like those on the International Space Station (ISS), can be incredibly tough on the human body. Astronauts face heightened risks of early-onset osteoporosis, insulin resistance, and significant muscle mass loss. Naturally, government space agencies want people whose bodies are more resilient to such pressures, and who can perform necessary duties without a ton of medical intervention.

According to Haig Aintablian, director of the UCLA Space Medicine Program, “just as pregnancy causes the body to undergo complex and unique changes, spaceflight also produces distinct and significant physiological changes.” It also requires its own medical specialty to manage (aptly called space medicine).

There’s a lot scientists don’t know, from the physical to the psychological. That’s a problem — for the future of science, space travel, and maybe even human existence at large.

NASA wants to go to Mars for research, and aims to send humans there as early as the 2030s. As the most similar planet to Earth in our solar system, Mars may have once harbored life, or may even currently. And in the future, we may even need it to support us.

Decades ago, seriously engaging with the idea of moving to Mars was extremely fringe for a multitude of reasons, ranging from a lack of technical feasibility to the desire to put scientific resources toward solving problems on Earth. Elon Musk — founder of the spaceflight company SpaceX — became a famed advocate for colonizing Mars in the early 2000s. He still is. Musk, who is currently worth around $410 billion, claims that he is only accumulating assets for the purpose of Martian space settlement. Last year, he said that he wants 1 million human settlers on the Red Planet in a self-sustaining city by 2050.

Now Musk isn’t alone. NASA experts, biologists, academics, futurists, disaster resilience researchers, and physicians are seriously considering the possibility of making humanity an interplanetary species.

“The biggest problem for humanity to solve is the guaranteed survival of our species — which the logical answer is to become multiplanetary,” Aintablian said. “I don’t think there’s a better solution than Mars.”

While we know some of the health effects of being on the ISS, we can’t really replicate the effects of Martian radiation exposure. Kelly Weinersmith — a biologist and co-author of A City on Mars: Can We Settle Space, Should We Settle Space, and Have We Really Thought This Through? — thinks that settling Mars on Musk’s timescale will be catastrophic. She argues that we shouldn’t rush to set up shop before understanding — and mitigating — the risks, even if this takes centuries rather than decades.

But many advocates for settling Mars are much more impatient. The only way to get there safely would be to unlock significant advances in space medicine, a nascent field that has just barely scratched the surface in its approximately 75-year history.

“Nothing that humanity has done that has been worthwhile has been easy,” Aintablian told me. “So much in our development as a civilization has been difficult, and the reason why we’re able to live such comfortable lives now is because of the extremely difficult challenges that humans have had to........

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