I love the idea of a greenhouse on Mars. There's something wonderfully ridiculous about traveling all that way through space and then getting excited because a little lettuce has survived. We'd be standing on another planet, looking out at a landscape no gardener on Earth has ever had to deal with, and somebody would still have to figure out what was wrong with the tomatoes. I'd absolutely want to hear about the tomatoes.
The bigger dream, though, is walking outside that greenhouse without a spacesuit. Terraforming is the idea of changing another world's environment to make it more like Earth, potentially allowing life from here to survive there without an enclosure. That's an enormous leap from keeping a few plants alive behind a sealed window, and it's the part of the space settlement conversation that leaves me both fascinated and a little uncomfortable.
Because once we start talking about changing a planet, I want to know what happens if we misunderstand something important. Who notices first, who gets to stop the project, and what have we changed by the time anybody agrees there's a problem? A beautiful illustration of a green Mars can skip straight past all of that, which is convenient for the illustration and considerably less convenient for whoever has to keep the air breathable.
Mars Has a Rather Significant Atmosphere Problem
Mars does have an atmosphere, but having one and being able to breathe it are very different things. It's extremely thin and made mostly of carbon dioxide, with only a tiny fraction of oxygen. NASA's Mars fact sheet also puts surface gravity at about 38 percent of Earth's, so even a much warmer Mars would still be a place with a fundamentally different physical environment. Turning up the temperature wouldn't change the planet's mass.
One familiar terraforming proposal involves releasing carbon dioxide trapped in ice and other reservoirs to thicken the atmosphere and trap more heat. In a 2018 study in Nature Astronomy, Bruce Jakosky and Christopher Edwards examined how much of that material could realistically be mobilized. They concluded that the accessible supply wasn't sufficient to accomplish the proposed transformation using present technology. The inventory matters, however enthusiastic we get about the idea.
NASA's explanation of that research makes one detail particularly striking: releasing the carbon dioxide in the polar caps would only roughly double the existing atmospheric pressure, still leaving it far below Earth's. Doubling sounds enormous until you notice where you're starting. I'd be delighted if somebody doubled my garden harvest, but doubling an atmosphere that's nowhere near suitable for us doesn't get us an outdoor farmers market.
There Are New Ideas, and They Still Have Limits
That study wasn't a declaration that every future warming method would be impossible. A 2024 paper in Science Advances modeled a different approach involving specially designed particles that could alter how Mars absorbs and loses heat. Under the researchers' assumptions, sustained release of those particles could produce substantial warming. This was a modeling result, with major uncertainties about things like how long the particles would remain airborne, rather than an experiment performed on Mars.
The researchers also explicitly distinguish warming from making the surface fully habitable. Their proposal doesn't supply a breathable atmosphere, and there's still the rather large matter of manufacturing, delivering and managing the material. I find the idea fascinating partly because it shows how much inventive thinking is happening, but a promising calculation and a planet people can live on have an awful lot of engineering between them.
It also makes me wonder how we'd judge success along the way. A temperature target might be met while the conditions needed for agriculture or life support remain out of reach. If a project changes the environment and then runs out of money, the people inheriting it would have to deal with the actual conditions, regardless of how lovely the original presentation looked. That's a future scenario worth considering before there are residents depending on the outcome.
We Already Tried Putting an Ecosystem Under Glass
Biosphere 2 is where my mind goes when somebody makes an enclosed garden sound self-sufficient simply because it contains plants. The facility in Arizona hosted its first two-year closure experiment from 1991 to 1993, with eight people living inside. The facility's historical account describes both impressive engineering and serious difficulty maintaining a balanced ecosystem. It also notes successful crop production, including strong rice yields, which makes the familiar version where absolutely everything failed a pretty unfair summary.
One particularly revealing problem involved oxygen. A 1994 paper by Jeffrey Severinghaus and colleagues reported that the oxygen concentration dropped from about 21 percent to 14 percent during the first 16 months. Their evidence pointed to microbes consuming oxygen as they broke down abundant organic material in the soil. Meanwhile, carbon dioxide from that respiration reacted with the building's concrete to form calcium carbonate.
That means the building itself was participating in the chemistry. The concrete wasn't simply holding up the experiment while the plants and people did the interesting stuff; it was helping change what remained in the air. I love that detail, although I suspect I would've appreciated it considerably less if I were living inside and trying to work out where the oxygen had gone.
Biosphere 2 wasn't an attempt to change another planet, and it didn't demonstrate that enclosed habitats can never work. It did provide an unusually memorable example of why putting familiar ingredients together doesn't guarantee a familiar result. My takeaway is that the soil, the walls and all the less photogenic parts deserve as much attention as the attractive green plants. The tomatoes can look wonderful while something important elsewhere in the system needs fixing.
The Microbes Would Be Doing a Lot of the Work
There is serious research into using biological processes for life support. ESA's MELiSSA program studies ways to recover useful resources from waste through connected biological and chemical processes, involving organisms such as bacteria, algae and plants. The aim is to recycle things a crew needs, including water and oxygen, and reduce dependence on supplies from Earth. That involves understanding and managing the different processes, rather than expecting a miniature forest to sort everything out on its own.
I realize that algae vessels and waste processing don't have quite the same promotional appeal as a sparkling city beneath a dome. They're the part I'm increasingly interested in, though. A future settlement would need people who are very good at noticing when the unglamorous machinery starts behaving differently, and who have the supplies and authority to do something about it.
A closed habitat would also make maintenance a much more personal subject. Down here, I can admire a plant without asking whether it's part of the system keeping everybody alive; in a future outpost, the equipment around that plant could be essential infrastructure. I'd want a tour that included the spare parts cupboard. A greenhouse full of gorgeous leaves would be exciting, but so would evidence that somebody had planned for a pump having a spectacularly inconvenient day.
We Have Made Oxygen on Mars, Which Is Pretty Wonderful
There has already been a real demonstration of making oxygen from the Martian atmosphere. NASA's MOXIE experiment, carried by the Perseverance rover, used an electrochemical process to extract it from carbon dioxide. Across 16 runs, the instrument produced a total of 122 grams of oxygen, with its final run in August 2023. It tested technology that could help future crews produce oxygen for breathing or rocket propellant.
I think that's extraordinary. It also makes the scale of the challenge easier to appreciate, because producing oxygen in an instrument is a different achievement from changing the air across an entire world. A settlement would need dependable production, storage and distribution, along with the other systems that make an enclosed environment safe. I'd celebrate the successful demonstration and keep asking what happens when the larger system needs repairing.
The People Inside Would Need a Life, Too
NASA studies isolation and confinement as real hazards of long missions. Sleep loss, workload and prolonged separation can affect health and performance, which is why researchers study ways to support crews. That doesn't tell us every future resident would be miserable, or that we already know what an entire community on Mars would feel like. It tells us that crew well-being belongs in the design from the beginning.
Then there's the distance. NASA's Mars communications overview explains that a signal can take roughly three to 22 minutes to travel between the planets, depending on where they are in their orbits. A conversation would have a delay before somebody on Earth even received the question, followed by another delay for the answer to get back. That's a long wait when you've asked for help, and a fairly formidable obstacle to the kind of rambling phone conversation where everybody interrupts everybody else.
I keep coming back to the ordinary details of living somewhere. Where would you go when you needed time alone, how much control would you have over your day, and could you decide you'd had enough and wanted to leave? Those questions seem easy to overlook when the conversation is all rockets and arrival dates. I'd want future residents to have a say in the answers well before anybody called the place home.
A World That May Already Have a Story
We still don't have confirmed life on Mars. NASA's Mars science objectives include investigating whether life exists there now and searching for evidence of life in its past. Evidence that an environment could have supported life is different from evidence that life actually developed there. That uncertainty is one of the most compelling reasons to keep exploring carefully.
Earth organisms arriving on another world are a forward contamination concern. Part of planetary protection is preserving our ability to investigate extraterrestrial environments without confusing material we've introduced with what was already there. Finding something biologically interesting and then having to ask whether we brought it along would be an incredibly frustrating outcome. We have a remarkable scientific opportunity, and I'd hate to muddle the evidence before we understand it.
A deliberately altered world could raise even bigger questions. If Mars has its own life, changing the conditions it depends on might harm it, although we can't predict the response of organisms we haven't discovered. If Mars has no life at all, its rocks and chemistry still preserve a history worth studying. I don't think a place has to grow something we recognize before it deserves careful attention.
This is where the word colonization starts to bother me. It can make a destination sound as though its main purpose is waiting for somebody to arrive and put it to use. I can be excited about exploration while still wanting us to ask what we might lose, and whether some places should be left alone. That's an ethical position, rather than a scientific discovery about what a planet wants.
Who Would Get to Make the Decisions?
Space already has a legal framework. The United Nations' overview of the Outer Space Treaty describes principles including the prohibition on national appropriation of celestial bodies, state responsibility for national space activities, and avoiding harmful contamination. So the popular idea that arriving first automatically makes an entire planet yours doesn't describe those principles. They also don't give us a complete, practical answer to every question a future settlement or terraforming proposal would raise.
I'd want to know who could approve a change affecting a whole planet, what evidence they would have to provide, and how other countries and future residents would participate. If a company stopped operating, who would keep essential systems running? Who would pay for equipment that couldn't simply be abandoned? Those are questions I'd want resolved while the project was still an idea, rather than after somebody else's survival depended on the answer.
There's also a difference between an experiment you can stop and a change you can reverse. Switching off a machine doesn't necessarily return everything around it to its previous condition. For any proposed planetary intervention, I'd want the testing to address what would remain afterward and how we'd notice effects we hadn't intended. An emergency stop button would be reassuring, but I'd want to know what it actually stopped.
I'd Still Love to See That Greenhouse
None of this has made me less interested in space. I still want to know what's beneath the dust, what the rocks can tell us, and whether living things ever got started somewhere beyond Earth. I also think a small, carefully studied habitat could teach us fascinating things about keeping people and plants alive, without requiring us to promise that an entire planet will become comfortable.
The part I struggle with is treating another world as somewhere we can move to when this one becomes inconvenient. Earth already supports the enormous variety of life we depend on, even when we do an impressively poor job of looking after it. Space research and caring for Earth can happen together. I just don't want a beautiful picture of a future Mars to make the planet beneath our feet seem disposable.
For now, my own connection to all of this is considerably less ambitious. I have an older version of this telescope that I absolutely adore, and I'm perfectly happy admiring the sky without having to arrange an oxygen supply first. I've also written about using the NeoRhythm wearable here on Earth; that personal interest doesn't establish it as treatment for the health risks of spaceflight. Neither piece of equipment is going to turn me into a Mars settler, although I do occassionally get carried away thinking about the gardening possibilities.
I hope we keep asking enormous questions and building clever things to investigate them. I'd also love for our excitement to include the people maintaining the equipment, the scientists protecting the evidence, and whoever eventually has to explain that the lettuce is doing beautifully but the rest of the system needs attention. There's plenty of wonder in learning how to be a careful visitor. We don't have to promise ourselves a second Earth before the first glimpse through that greenhouse window can be extraordinary.
Related Reads You Might Enjoy
Sources
Jakosky and Edwards. Inventory of CO2 available for terraforming Mars. Nature Astronomy, 2018.
Ansari and colleagues. Feasibility of keeping Mars warm with nanoparticles. Science Advances, 2024.
Severinghaus and colleagues. Oxygen loss in Biosphere 2. Eos, 1994.
NASA Office of Safety and Mission Assurance. Planetary protection.
