Should Humans Plan to Live on Mars? Probably Not Anytime Soon

In one sentence: Biologist Kelly Weinersmith and her partner Zach Weinersmith spent four years researching whether humans could actually settle Mars, writing it up as A City on Mars — and their conclusion is that radiation, low gravity, reproduction, and food are all still unsolved, which makes near-term "Mars colonization" talk mostly marketing rather than a real plan.

Key Findings

• Mars wins the three-way real-estate contest, but it's still "a harsh environment." The book weighs the Moon, Mars, and building an orbital space station: "The Moon, Mars, or creating an orbital space station. And among those, Mars is overwhelmingly the best option" (Zach). Kelly's reasoning: "space is huge, and Mars is relatively close"; the Moon is severely carbon-poor (humans are carbon-based life), while Mars has both more carbon and abundant water that's "not too hard to get."
• There's almost no radiation shielding, so settlement means burying yourself. Mars lacks a global magnetosphere, and its atmosphere is "only 1% as thick as what we have on Earth," so "most of that radiation hits the surface" (Kelly). The one-way trip takes a minimum of six months with current technology, and a spacecraft's own shielding is "probably not quite enough." Most proposals bury habitats several meters under the Martian dirt — "We're living like mole people underground" (Kelly) — instead of the glass domes in artist renditions.
• Hip bone density drops about 1% a month in zero gravity, and 437 days was, as of this taping, the longest anyone had stayed in space. Zach cites the figure directly: "about 1% bone loss in the hip per month." Only a handful of people have ever reached a full year up there. Mars's surface gravity is roughly 40% of Earth's, and whether that's enough to avoid the same bone and muscle breakdown is unknown: "we don't know is the problem" (Zach).
• Getting pregnant isn't the hard part — growing up to reproductive age in that environment is. Zach describes existing space-reproduction research as "a grab bag of experiments... some invertebrates, some vertebrates, a very small number of, like, rodent studies, nothing even close to a human," and notes that no generational study on vertebrate mammals in a space-like environment exists. What data there is isn't encouraging: rat mothers sent to space during part of their pregnancy came back to Earth needing labor contractions "twice as often" (Kelly).
• Martian regolith is laced with perchlorates, and that threatens the whole food chain. Perchlorates are endocrine-disrupting chemicals that "mess with metabolism in adults and fetal development for children" (Kelly). Plants grown in perchlorate-laced soil pull the chemical straight into their tissue, so settlers likely need hydroponics instead of Martian dirt — and they can't bring livestock like chickens or cows because "they're too big... too messy... too hard to keep alive," leaving a choice between vegetarianism or eating insects for protein.
• The people who've flown to space are a wildly unrepresentative sample. The overwhelming majority have been middle-aged men; the U.S. program didn't admit women until 1978 (Zach notes Russia flew women twice before that, without giving specific dates); roughly 10% of everyone who has ever been to space is a woman; and there is essentially no data on how infants or teenagers would fare.

Scientific Background

Earth's global magnetosphere and thick atmosphere deflect most cosmic radiation and solar particles; the ISS still sits inside that magnetic shield, so astronauts there absorb far less radiation than they would traveling between planets. Mars has neither — no global magnetic field and an atmosphere just 1% as thick as Earth's — which is the physical reason the episode keeps landing on "bury the habitat."

Zero gravity aboard an orbital station and Mars's roughly 40% partial gravity are physically different environments. Most of the hard data — the ~1% monthly hip bone loss, the fact that merely walking after months in space is "considered very impressive," the loss of the baroreflex (the reflex that keeps blood pressure stable when you stand up, whose failure causes dizziness) — comes entirely from zero-gravity studies. Whether Mars's partial gravity is enough to let a human body develop and function normally has no controlled data behind it yet; "we don't know" is the honest, recurring answer in this episode.

Perchlorates are hormone-disrupting chemicals, and plant roots don't distinguish "nutrient" from "perchlorate" — they pull both into stems, leaves, and fruit, which is the hidden catch in growing food locally on Mars. Compounding that: living underground for radiation protection means no sunlight, and the human body needs sunlight to produce vitamin D, which in turn is essential for turning calcium into bone. Break that chain and it compounds whatever bone damage low gravity has already done — a problem Kelly flags as especially dangerous for pregnant women and developing infants.

People

Kelly Weinersmith — a biologist and science writer, "an ecologist by training" who specializes in parasitology ("I'm a parasitologist, so I study parasites"). She and her partner Zach Weinersmith spent four years researching space settlement for their book A City on Mars (referred to on air simply as "a book called City on Mars"), which works through everything a Moon, Mars, or orbital settlement would need to solve — from whether human bodies can survive there, to safe childbirth, to how such communities would be governed. She closes the interview by admitting the research deepened her attachment to Earth: "I really appreciate this planet that we evolved on and we're so well adapted to. I'm staying here."

Zach Weinersmith — Kelly's partner and co-author on A City on Mars. He delivers the book's central thesis in one line — "there is no plan B": even if Elon Musk wants to "put on a cowboy hat and fly off to Mars and start his Martian city," abandoning "this polluted planet... to its wars and devastation," he's "a fool," because Mars is so hostile that not even $10 trillion spent zapping Earth with asteroids, unleashing every disease imaginable, and starting a couple of nuclear wars could make Earth as bad as Mars already is — "That's how desolated everywhere else in the solar system is."

Odd Details & Trivia

• The episode opens with a hype montage: unnamed Speaker 1, 2, and 3 declare, in turn, that "thousands of people are going to colonize Mars" soon, that they'd "love to see a trillion humans living in the solar system," and that the next Mars launch window (2026) means a mission "in a couple of years' time" isn't out of the question — capped by Elon Musk's own voice: "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." That montage sets up exactly the hype the interview goes on to puncture.
• Zach's dig at social media's Mars romance: bring up going to Mars on Twitter and someone posts "a GIF of a guy walking toward the horizon dramatically," but life on the ISS is mostly "scrubbing the toilets and making sure there's not too much mold and cooking dinner... and managing interpersonal relationships" — "It's a lot like Earth."
• "We're living like mole people underground" got an on-air laugh (marked [LAUGHTER] in the transcript) — the most vivid rebuttal in the episode to the glass-dome artist renditions of Mars bases.
• Asked whether she'd eat insects for protein, Kelly admits: "I've got to admit, it's not for me."
• Among the daily-life questions Kelly rattles off is "How do you govern these communities?" — raised but never explored further in this episode; governance and space law simply aren't on the table here.
• Credits: produced by Jessica Yung, edited by showrunner Rebecca Ramirez, fact-checked by Tyler Jones, engineered by Gilly Moon; Beth Donovan is senior director and Collin Campbell is senior VP of podcasting strategy.

Cross-Domain Connections

No direct connection to the acquired (business-history) domain yet: acquired has a Tier 0 mirror of a SpaceX episode (sources/acquired/2020-05-26_spacex_en.md) that hasn't been extracted to Tier 1, so Musk's "multiplanet species" soundbite and Zach's "cowboy hat" jab have no page to link against — not forced here.

Same two guests (Kelly & Zach Weinersmith), same book (A City on Mars), a different conversation: Short Wave interviewed them again on 2025-04-21 in shortwave-mars-colonization-en. The two episodes overlap roughly 23% but are otherwise distinct conversations — sibling episodes, cross-linked via the related field.

Pages to Build

• mars-settlement — the core obstacles to human Mars settlement (radiation shielding, partial-gravity physiology, reproduction and child development, perchlorates/food chain). This episode and its sibling shortwave-mars-colonization-en draw on the same book, so a merged page could track A City on Mars's recurring arguments across both.
• space-radiation — the specific physical constraint (no magnetosphere, atmosphere at 1% of Earth's, underground habitats as the only current answer) that will likely recur across other space-exploration episodes (Artemis, deep-space missions, etc.).

Source · shortwave