The Short Version
We’re fact checking the science in The Martian, by Andy Weir. Could you really grow potatoes on Mars, make water out of rocket fuel, or drive across a planet in a homemade camper?
Here’s the quick answer. The chemistry, the engineering and the orbital math are mostly solid, and the book earns its reputation. There is one big cheat in the very first chapter, a few friendly shortcuts, and a couple of real problems it never mentions. Light spoilers ahead for the middle of the book, nothing about the ending.
The Storm
Let’s start with the cheat. The book opens with a storm so violent that the crew abandons the mission, with winds of one hundred seventy-five kilometers per hour. And it’s the part scientists love to pick on. Mars has an atmosphere less than one percent as dense as Earth’s, about six or seven millibars at the surface, compared with more than a thousand on Earth.
NASA’s Dave Lavery told Popular Science that a hundred mile an hour wind on Mars would push on you like an eleven mile an hour breeze on Earth. And NASA Goddard’s Michael Smith told Space.com that you would feel a breeze, not get knocked over. One report says Weir himself calls it the plot’s biggest inaccuracy. I couldn’t find his original statement, so treat that part as secondhand.
The Dust That Is Real
But dust storms are real, and they are a genuine threat in a different way. The danger isn’t wind, it’s darkness. In two thousand eighteen, a planet-wide dust storm blotted out the sun over the Opportunity rover, which runs on solar power. Its last contact was on June tenth, and NASA declared the mission over in February twenty nineteen.
The book uses exactly that danger much later, when a storm cuts the sunlight his rover depends on. So Weir swaps the wind for the real threat, the light, and it is more convincing the second time around.
Potatoes And Soil
Now the farm. Mark grows potatoes in Martian soil mixed with Earth soil and human waste. Is that plausible? In twenty sixteen, the International Potato Center and NASA started growing potatoes in Peru, in desert soil from the Atacama that NASA scientist Chris McKay called the most Mars like on Earth. And Wageningen University in the Netherlands grew radishes, peas, rye and tomatoes in simulated Martian soil, which passed a heavy metal screening.
Night soil, human waste as fertilizer, is also a real practice. But those experiments use simulated soil, not the real thing, and the book skips a real problem. In two thousand eight, NASA’s Phoenix lander found perchlorate in Martian soil, a salt that can harm plants and, in large doses, the human thyroid. I didn’t find perchlorate mentioned anywhere in the book.
Water From Rocket Fuel
Next, the most famous science scene: making water. Mark takes hydrazine, the fuel in the lander’s thrusters, passes it over a catalyst, and gets nitrogen, hydrogen and some leftover ammonia. That is real chemistry. Hydrazine thrusters use an iridium catalyst to break it down, and burning the hydrogen with oxygen gives you water.
He also explains why it’s dangerous, and the book is right to be scared. Hydrogen in a room full of oxygen is a bomb. The numbers are generous, and his chemistry shortcuts are quick, but the principle is textbook.
Air From The Sky
The oxygen side is also grounded. Mars’s air is about ninety-five percent carbon dioxide, which is exactly what the book says, and NASA has made oxygen from it. An experiment called MOXIE rode on the Perseverance rover and produced a total of one hundred twenty-two grams of oxygen over sixteen runs, with a peak of twelve grams an hour.
So the idea is proven, but the scale isn’t. Mark makes liters of oxygen at a time, with machines the size of furniture. And his equipment keeps running far longer than it was ever designed to, which is a very generous reliability record.
The Habitat
The habitat itself is a canvas dome, held up by air pressure, and that’s less fanciful than it sounds. NASA has tested inflatable modules, and BEAM, an expandable room, was photographed attached to the International Space Station in two thousand sixteen. The book’s canvas, which fails at a stressed seam, is a nicely observed engineering detail.
The real catch is the pressure difference. Inside is one atmosphere, outside is under one percent of that. Any breach isn’t a gentle leak, it’s an explosive release, and the book treats it that way.
Radiation
Here’s what the book mostly skips. Mars has no global magnetic field. Mark mentions that, with a joke about getting cancer, and it is true, though it has patches of magnetized crust. Curiosity’s radiation detector measured about zero point six four millisieverts per day on the surface, and one point eight per day on the trip.
By my arithmetic, five hundred forty-nine sols on the surface would add about three hundred fifty millisieverts, before counting the flights. And a twenty twenty-one National Academies report recommended a career limit of six hundred. So Mark’s stay alone would eat more than half of that lifetime allowance, and the book hardly mentions it.
The Nuclear Heater
Then there’s the radioactive heater. In the book, a plutonium powered generator, an R T G, keeps his rover warm, and the crew buried it four kilometers from the base for safety. Real R T Gs turn the heat of decaying plutonium two thirty-eight into electricity. NASA’s current model makes about one hundred ten watts of power from roughly two thousand watts of heat.
The book’s numbers, a hundred watts from fifteen hundred, are in the right neighborhood. Using one as a space heater is a clever idea. The part that’s fiction is the convenience, because I doubt anyone would pack a plutonium generator next to a person for weeks.
Pathfinder
This one is my favorite. Mark drives to the site of Mars Pathfinder, a real probe that landed on July fourth, nineteen ninety-seven, with a small rover named Sojourner. In reality, its last successful transmission came on September twenty-seventh, and NASA ended the mission in March nineteen ninety-eight.
Sojourner was only planned to work for seven days, and it lasted eighty-three. Reviving a probe after decades with spare parts is the fiction. But a dead lander is still a great radio if you give it power and warmth, and I wish that were true.
Ion Engines And Hermes
The ship Hermes uses ion engines, and this part is real. NASA’s Dawn spacecraft used them, and each engine produced about ninety-one millinewtons of thrust, roughly the weight of a sheet of paper. At full throttle it would take four days to go from zero to sixty miles an hour. But it runs for years, and the speed adds up.
What’s fiction is the power. Hermes carries a nuclear reactor big enough to push a crewed ship, and a spinning section that gives crew a partial gravity. To my knowledge, no crewed spacecraft has spun for gravity, and no crew has flown an ion drive that strong. It’s the book’s most optimistic technology.
The Gravity Trick
In the middle of the book, a NASA astrodynamicist comes up with a maneuver that uses Earth’s gravity to turn Hermes around. Gravity assists are real, and missions like NASA’s Lucy use flybys of Earth to change course. A crewed flyby of Mars is real too, at least on paper. A private group called Inspiration Mars proposed a five hundred one day loop in twenty thirteen, though it never flew.
So the math is plausible. What’s fiction is the timing, the way the booster, the probe and the launch window all line up within a few weeks. That’s drama, not physics, and I’m happy to give it a pass.
Talking To Earth
Communication gets a lot of attention, and it’s well done. Radio signals between Earth and Mars take between about three and twenty-two minutes each way, depending on where the planets are, so you can’t chat. The book’s delays of a dozen minutes or more are right in range.
And the idea that orbiters can watch a base is real too. NASA’s Mars Reconnaissance Orbiter camera has photographed Curiosity while it was driving. Whether a message made of rocks could be read from orbit, I can’t say.
The Rocket
The climax involves launching a stripped down ascent vehicle, with the hull open and canvas over the hole. Real Mars ascent rockets are on the drawing board, for bringing samples home, and NASA has published animations of them. But nobody would launch a person in a ship with its nose removed, and the book knows it, which is why it’s a joke.
The principle behind it is real though: weight is everything, and fuel is cheap if you make it on site, which is why the most absurd scene still feels like engineering.
The Scorecard
Here’s my score. Chemistry gets four and a half out of five. Engineering gets four. The Mars environment gets three, because of that storm and the radiation. Spaceflight gets four. And human factors, meaning radiation, food and mental health, gets three. That averages to three point seven, which for a thriller is very high.
What matters is that the book teaches real ideas, and when it cheats, it does so on purpose.
Where To Get It
That’s the science of The Martian. Mostly real, one big cheat, and a lot of love for engineering. If you want my opinion of the story itself, I have a spoiler free review, and I have another video for the ending, with full spoilers.
The book, the audiobook and every book I mentioned are linked in the description. Tell me in the comments: which piece of Mars science do you most want to see tested for real? Thanks for watching, and subscribe for more fact checks.
