Moving to Mars: 5 Truths That Pop the Hype Bubble

The episode opens with a highlight reel of hype. One voice after another: "We're going to Mars, not just a few astronauts. Thousands of people are going to colonize Mars, and I am telling you that they're going to do this soon." Another: "I would love to see a trillion humans living in the solar system." A third points out that the next Mars launch window opens in 2026, so "you wouldn't rule out seeing some sort of mission there in a couple of years' time." Then Elon Musk's own voice closes it out: "One path is we stay on Earth forever, and then there will be some eventual extinction event. The alternative is to become a spacefaring civilization and a multiplanet species."

Sounds thrilling, right? So thrilling that NPR's science show Short Wave brought on two people whose entire job, for this episode, was to gently deflate it: biologist Kelly Weinersmith and her partner Zach Weinersmith, who spent four straight years researching whether humans could actually settle Mars and turned it into a book called A City on Mars. Their conclusion isn't "it's impossible." It's something sharper: there is no step in this plan you get to skip just because you said it with enough confidence. Here are the five truths from the book that do the most damage to the hype.

Warm-Up: Why Mars, Of All Places?

The book first sizes up three candidates: the Moon, Mars, and building your own space station from scratch. Zach's verdict is blunt: "The Moon, Mars, or creating an orbital space station. And among those, Mars is overwhelmingly the best option." Kelly's reasoning is almost embarrassingly simple: "space is huge, and Mars is relatively close." The Moon is nearly out of carbon, and since we're carbon-based life, that's a dealbreaker before you even start. Mars has more carbon, plus water that's "not too hard to get." So Mars wins the contest. Winning the contest is not the same thing as passing it.

Truth #1: You Won't Live Under a Glass Dome — You'll Live in a Basement

Every Mars concept-art poster shows a shining glass city under a pink sky. Here's the problem: Mars has no global magnetic field, and its atmosphere is "only 1% as thick as what we have on Earth." Translation from Kelly: "most of that radiation hits the surface." The International Space Station is relatively safe because it's still tucked inside Earth's magnetic shield. The trip to Mars is not — it takes a minimum of six months one-way with current technology, and a spacecraft's own shielding is "probably not quite enough." The only plan anyone's got is to bury the habitat several meters under the Martian dirt. As Kelly put it, laughing on air: "We're living like mole people underground." Funny line. Not a joke about the science.

Truth #2: Nobody Actually Knows If Low Gravity Is Safe

Two different environments get mixed up all the time. The "zero gravity" astronauts experience on the ISS and the roughly 40% gravity you'd feel standing on Mars are not the same thing.

The catch: "we have no data" and "there's no gravity" are two different problems. Every number we have on bone loss comes from zero-gravity studies: astronauts lose about 1% of their hip bone density per month, and as of this recording, 437 days was the longest anyone had ever stayed in space — just walking normally after a few months up there counts as "very impressive," partly because the body also loses the reflex that keeps your blood pressure steady when you stand up, which is why astronauts get dizzy. But Mars isn't zero gravity — it's about 40%. Nobody has ever run the experiment to find out whether 40% is enough for a human body to build bone normally, gestate a baby normally, or just function normally over years.

Zach's answer to "is 40% gravity enough?" is refreshingly blunt: "we don't know is the problem." A book built on four years of digging through data, and its most solid conclusion is "we don't know" — which is exactly why you should trust it.

While we're popping bubbles: forget the dramatic GIF of an astronaut striding toward the horizon that shows up every time Mars comes up on social media. Real ISS life, per Zach, is mostly "scrubbing the toilets and making sure there's not too much mold and cooking dinner... and managing interpersonal relationships." His summary: "It's a lot like Earth."

Truth #3: Getting Pregnant Isn't the Hard Part — Growing Up Is

Zach calls the existing research on reproduction in space "a grab bag of experiments... some invertebrates, some vertebrates, a very small number of, like, rodent studies, nothing even close to a human." Nobody has ever run a multi-generation study — meaning nobody knows whether a kid born in space could grow up healthy enough to have kids of their own. The little data that does exist isn't reassuring: rat mothers sent into space partway through pregnancy came back needing labor contractions "twice as often" as normal. This isn't the book being dramatic for effect. It's the book being honest about where the map runs out.

Truth #4: Martian Dirt Is Toxic — Get Ready for Hydroponic Veggies (and Maybe Bugs)

Martian soil is loaded with perchlorates, hormone-disrupting chemicals that "mess with metabolism in adults and fetal development for children." Plant roots can't tell the difference between a nutrient and a poison, so anything grown straight in Martian dirt pulls the perchlorates right up into its stems, leaves, and fruit. That means settlers would almost certainly need hydroponics instead of actual soil — and forget bringing chickens or cows, because, as Kelly put it, "they're too big... too messy... too hard to keep alive." Protein comes down to two options: go vegetarian, or eat insects. Asked how she'd feel about the bug option, Kelly didn't dress it up: "I've got to admit, it's not for me."

Truth #5: Almost Everyone Who's Flown to Space Is a Middle-Aged Man

The U.S. space program didn't let women fly until 1978 (Russia had already flown women twice before that, though no exact dates are given). Even today, roughly 10% of everyone who has ever been to space is a woman. Data on infants and teenagers in space is essentially nonexistent. In other words, if humanity ever actually settles Mars instead of just visiting it, the first people carrying all the unknown risk are far more likely to be people like you than the guy in the cowboy hat announcing it on stage.

So Maybe Don't Sell Your House on Earth Just Yet

Zach delivers the hardest line in the whole episode. Even if Elon Musk really does "put on a cowboy hat and fly off to Mars and start his Martian city," leaving "this polluted planet behind to its wars and devastation" — he's "a fool," because Mars is so brutal that you couldn't spend $10 trillion, "zap us with asteroids," unleash every disease imaginable, and start a couple of nuclear wars, and still not make Earth as wrecked as Mars already is. "That's how desolated everywhere else in the solar system is." Short version: there is no plan B.

After four years of research, Kelly's own takeaway lands even quieter: "I really appreciate this planet that we evolved on and we're so well adapted to. I'm staying here." That's not an argument against exploring space — of the three real-estate options, Mars is still the least terrible, and people will probably go someday. It just means the next time someone promises "thousands of colonists within a decade," you've now got a few sharp questions ready: radiation, gravity, babies, food — which of those did they actually solve?