Why Humans Born on Mars May Never Return to Earth; Elon Musk's Plan Faces Brutal Reality Check

From shrinking bodies and weakened immune systems to dangerous childbirth complications, life on the Red Planet could fundamentally alter what it means to be human, according to Rice University professor Scott Solomon.

Elon Musk’s vision of building a human settlement on Mars by 2050 may sound like a giant leap for humanity, but a leading scientist is warning that the reality could be far more brutal for the human body than many imagine. From shrinking bodies and weakened immune systems to dangerous childbirth complications, life on the Red Planet could fundamentally alter what it means to be human, according to Rice University professor Scott Solomon. In his upcoming book, Becoming Martian: How Living in Space Will Change Our Bodies and Minds, Solomon lays out the profound biological risks that could accompany humanity’s push beyond Earth.

One of the biggest unanswered questions, Solomon argues, is whether humans can even reproduce away from their home planet. It remains unknown if a child could be safely conceived, carried, and born in space or on Mars, where gravity is far weaker and radiation levels far higher than on Earth.

In Becoming Martian, Solomon notes that there have been no confirmed cases of people having sex in space and very little research into how a fetus might develop or how childbirth would unfold in a low-gravity environment. The long-term evolutionary consequences of living on Mars are equally uncertain, though Solomon believes humans could become physically smaller and potentially unable to return to Earth.

Speaking to the Daily Mail, Solomon said, "We're at a moment right now when history is happening in terms of people actually pushing the envelope of going deeper into space. I think what readers might find interesting is learning a bit more about what would happen if those efforts are successful. That's the story that I try to tell here - let's imagine what happens next."

While researching his book, Solomon consulted dozens of experts from NASA, SpaceX, and other space-focused organizations. One revelation stood out above all others: "how little we know about reproduction in space."

"The idea of building a settlement, a city, on another planet or somewhere in space, kind of assumes that people can go there and have children and raise a family," Solomon said. "Could we have children on Mars? I think that's still an open question," he added. "And if the answer is no, or if the answer is yes, but there are issues, we need to know that, I think, before we should start moving forward with plans to actually create settlements beyond Earth."

Mars’ gravity is only about one-third as strong as Earth’s, and studies of astronauts have already shown that prolonged exposure to low gravity causes significant bone density loss. For women born on Mars, that could make childbirth far more dangerous.

"We know childbirth is already risky, and so we could imagine a scenario where women who are born on Mars are at even greater risk of complications during childbirth," Solomon said.

He added that Mars’ environment may eventually favor humans with denser bones, "so that they can basically afford to lose bone density as they age."

Over generations, Solomon believes these pressures could result in Martians becoming smaller than Earth-born humans. "We know that on islands on Earth, animals often get smaller or get larger, and that's known as the island rule, which I described in the book," he said. "It's possible that we could see either larger or smaller Martians. I argued that smaller might be more likely for a number of reasons, one of which is the smaller you are, the fewer resources you need to consume." "And especially in the early days of a settlement on Mars, those resources might really be quite limited, and there might be an advantage to needing less of them."

Even if a colony succeeds, Solomon warns that Mars-born humans may never be able to visit Earth. The planet’s vast and complex microbial ecosystem could pose serious health risks to someone whose immune system evolved in isolation.

"One of the biggest challenges might be our immune systems," Solomon said. "Here on Earth, we are exposed to a huge number of microorganisms." "If we go to Mars, we will take only a very tiny fraction of all of those microbes with us... A child born on Mars would be only exposed to that tiny fraction of microbes that make it all the way to Mars." "So if they came back to Earth, a lot of the microorganisms that we interact with on a regular basis that aren't harmful to us because our immune system is used to them - they could be really dangerous to a person from Mars."

In his book, Solomon compares this risk to the devastation caused when European explorers introduced new diseases to Indigenous populations in the Americas.

Beyond biology, Becoming Martian also explores how Martian society might evolve culturally and politically. "The first people that go to Mars will almost certainly still feel very connected with Earth," Solomon said. "But with each generation born on Mars, I think they will increasingly identify as being Martian, even though they'll have this Earth heritage."

That divide could deepen if travel between planets remains difficult. "If I'm right that it will be hard to [travel between planets] because of the risk of getting sick, for example, then you might start to see them (Martians) become quite distinct culturally, politically, as well as biologically," he said.

Communication delays — up to 20 minutes one way — would further separate the two worlds, making real-time conversations impossible.

While many argue humanity should focus on fixing Earth before colonizing space, Solomon believes the two goals need not be mutually exclusive. "It's absolutely important for us to dedicate a lot of attention and resources to solving our problems on Earth," he said. "But I think that we should be able to do that while also learning about what it's like in space and whether we might someday be able to live there."

Despite all the risks, Solomon admits the pull of Mars is strong. "I love to travel. I love adventures. I'm a scientist, I'm a curious person. I would love the opportunity to go and explore," he said, adding, "But I would want to come back home."