Elon Musk says SpaceX wants to build a “self-growing city” on the Moon, potentially within a decade, while still pursuing a future city on Mars.
That sounds audacious, futuristic and—if you’re a science-fiction fan—pretty exciting. But before we start talking about cities on other worlds, there’s a surprisingly basic question we should probably answer:
Can humans reproduce there?
I recently encountered that question in Kelly and Zach Weinersmith’s excellent book A City on Mars, and it stopped me cold. Because the answer is: we really don’t know.
Visiting Isn’t Settling
We’ve been sending humans into space for more than sixty years. We know a great deal about how adults respond to microgravity, at least over periods of months.
But a city is fundamentally different from a research station.
A permanent settlement requires people to have children. Those children have to develop normally, grow into healthy adults and eventually be capable of having children themselves. That means conception, pregnancy, fetal development, birth, childhood and adolescence all have to work in an environment radically different from Earth.
And our data on that is astonishingly thin.
The International Space Station gives us information about microgravity, but the Moon has one-sixth Earth gravity and Mars about one-third. We have essentially no direct mammalian data about reproduction across a full life cycle in either of those gravity levels. Existing animal experiments have been limited and sometimes produced troubling or ambiguous results.
We don’t even know whether a developing fetus depends on gravitational cues that might be disrupted at partial gravity.
Then There’s Radiation
Gravity isn’t the only concern.
Earth provides us with an atmosphere and magnetic field that shield us from much of the radiation found beyond our planet. The Moon and Mars offer far less protection.
Radiation is concerning enough for adults. For rapidly dividing fetal cells and developing children, the stakes could be much higher.
The Weinersmiths also point out that settlement means thinking far beyond pregnancy itself. Even if a baby is born apparently healthy, what happens during childhood? During a teenage growth spurt? Do bones and organs develop normally under reduced gravity? Could someone raised on the Moon ever safely live on Earth?
We simply don’t know.
The Experiment Nobody Wants to Run
And here’s where the problem becomes uncomfortable: Science normally answers unknowns with experiments. But how exactly do you ethically experiment with human fetal development in an environment where you have good reason to suspect something might go wrong?
You can study cells. You can study animals. You can put rodents into altered-gravity environments and follow multiple generations.
Eventually, though, if we really intend to create permanent settlements, someone has to become the first pregnant human exposed to lunar or Martian gravity.
Someone becomes the first fetus.
That someone becomes the first child whose development answers questions we couldn’t answer beforehand.
The Weinersmiths make the uncomfortable point that simply sending people to Mars and letting them begin families would amount, in effect, to human experimentation.
That’s hard to square with the casual way we sometimes talk about “colonizing Mars.”
A City Requires Children
None of this means humans can’t eventually live permanently on the Moon or Mars.
Maybe partial gravity will prove sufficient. Maybe shielding will solve the radiation problem. Maybe technologies we haven’t invented yet will make reproduction much safer.
But those are maybes.
There’s an enormous conceptual leap between saying we can send humans there and saying humans can build a civilization there.
A rocket can get adults to the Moon.
A habitat can keep them alive.
A city requires something more.
It requires babies who can grow up healthy.
Before we talk too confidently about building cities on other worlds, we should probably find out whether humans can reproduce in space without turning those first children into an experiment.
Jayson L. Adams is a technology entrepreneur, artist, and the award-winning author of The Quantum Mirror, Ares, and Infernum.
His novels blend high-stakes science fiction, psychological tension, and character-driven suspense. Explore the books at www.jaysonadams.com.