Will Mars Colonists Ever Come Home? The Gravity Problem

Jan de Vries · 2026-08-13

When we picture life on Mars, most of us imagine red dust, domed habitats, and astronauts taking cautious first steps. But there's a quieter, more unsettling question that engineers and space medicine experts are wrestling with right now: what happens to the human body after years of living in low gravity? Harry Margulies digs into whether Mars colonisation could become a one-way trip—not because of rockets or fuel, but because our own biology might make the return journey impossible. ### The Low-Gravity Reality Mars has about 38 percent of Earth's gravity. That sounds manageable, but it's a completely different world for the human body. On Earth, gravity constantly pulls on our bones, muscles, and fluids, telling our systems to stay strong and dense. On Mars, that constant tension is gone. Over time, astronauts would face: - Bone density loss that could reach 1 to 2 percent per month in the worst cases - Muscle atrophy, especially in the legs and lower back - Changes in vision due to fluid shifting toward the skull - Weakened cardiovascular systems that struggle to pump blood effectively These aren't just theoretical concerns. We've seen them in astronauts who spend six months on the International Space Station, which orbits at zero gravity. Mars's gravity is weaker than Earth's, but it's not zero—so researchers are still figuring out exactly how the body would respond to that middle ground. ### The One-Way Ticket Argument Here's where the conversation gets uncomfortable. If settlers stay on Mars for years, their bodies may adapt to the lower gravity so completely that returning to Earth becomes physically dangerous. Imagine spending five years on Mars, then trying to stand up in Earth's gravity. Your bones might be too fragile. Your muscles might not be able to support your own weight. Your heart, which has learned to work less, could struggle to push blood against the stronger pull. Some experts argue this means the first Mars settlers should be considered permanent residents. It's not a failure of the mission—it's a biological reality. You'd be trading one home for another, knowing that the trip back could break you. ### What Adaptation Really Means Adaptation isn't just about surviving on Mars. It's about your body making choices without your conscious input. Over months and years, your cells respond to the environment. Your skeleton becomes lighter and more porous. Your balance system recalibrates. Your sleep patterns shift to a 24.6-hour day. In a strange way, you become Martian. That adaptation is beautiful and terrifying at the same time. It means humans are incredibly flexible. But it also means that returning to Earth might feel like moving to a planet with its own hostile gravity—one that your body no longer recognizes. ### The Hard Question We Need to Answer Colonising Mars is often framed as a grand adventure, and it is. But the low-gravity problem forces us to ask a deeper question: are we sending people on a mission, or are we founding a new branch of humanity? If the answer is the latter, then we need to be honest about what that means. Future settlers should know, before they board that rocket, that they may never walk on Earth again. They should understand that their children, if any, might be born with weaker bones and different cardiovascular systems. They should accept that their bodies will belong to Mars, not Earth. That doesn't make the adventure less meaningful. But it does make it heavier. And it's a weight that every future colonist—and every person cheering them on—needs to carry together. ### The Bottom Line Mars might be humanity's greatest adventure, but it's also a one-way door for the people who step through it. The low-gravity problem isn't a technical glitch we can engineer away. It's a fundamental part of living on a smaller planet. As we plan the first missions, we need to plan for permanent settlement—because the human body may not give us any other choice.