The discussions ranged from the practical (how can directed evolution make microbes more tolerant of Martian conditions?) to the pragmatic (what things that astronauts most need can be produced by microbes?) to the seemingly preposterous (how to send a billion “solar sails” into orbit around Mars, to reflect terawatts of warming sunshine onto the surface).
The purpose of the workshop, titled “Green Mars”, was to develop an “up-to-date perspective on the feasibility of terraforming Mars”. Such terraforming, which would consist of re-engineering the frigid, all-but-airless, radiation-baked and seemingly lifeless planet in order to make it habitable, has been discussed in scientific journals since the early 1970s.
But despite the idea making it onto the cover of Nature, a prestigious journal, in 1991, it has hardly entered the mainstream. For the most part it has remained the preserve of an academic fringe fascinated by thought experiments and the producers and consumers of science fiction, realms which often overlap.
This is now changing. The series of launchers developed by SpaceX—partially reusable today, quite possibly entirely so within a year or two—are rapidly reducing the cost of getting to orbit. The potential for sending payloads and people to Mars is therefore becoming plausible in a way that it never has before.
Mars is not an accidental beneficiary of a general technological trend. It is to a large extent the original cause. Elon Musk, SpaceX’s boss, has been talking for decades about settling the planet one farther out from the Sun. It is this that has led him to push back the frontiers of rocketry. Specific pronouncements Mr Musk makes about the timing and ambition of his plans for putting people on Mars are best treated with a scepticism born of long experience. But he has done a huge amount to make the idea more plausible than ever.
Look at those cavemen go
Others are following in SpaceX’s slipstream. They do not all share Mr Musk’s obsession with Mars; but they are all interested in expanding the human realm beyond Earth. America’s government is interested in using the newly cost-effective commercial hardware offered by SpaceX and its would-be rival, Blue Origin, to further its plans to return astronauts to the Moon in the next few years. China wants to use its own increasingly impressive capabilities to the same end. A number of private companies believe that the sort of agile development which made today’s launch systems possible means there could be a promising business in building private space stations to accommodate researchers, government-funded astronauts and private citizens.
Jed McCaleb, a software billionaire responsible for various blockchain innovations, owns one of those companies, VAST. He hopes to see it launch its first space station, Haven-1, in 2026, and imagines a profitable future thereafter. But that is not the only reason he is doing it. “I believe that people need to get out into the solar system,” he says. “If you’re just limited to Earth, the world becomes, like, very zero sum. We need a place to push out into.”
Orbital habitats are a beginning. But if this sort of frontier mindset has a natural home in the solar system, it is Mars. It is with that in mind that, through a non-profit organisation called the Astera Institute, Mr McCaleb has become the leading funder of research into terraforming Mars, and was thus the sponsor of the Berkeley meeting. A source of funds and the prospect that people will actually be going to Mars before too long probably explains the new interest in terraforming on their own. But there is a broader intellectual context, too: the creation of what Robin Wordsworth, a researcher at Harvard University, calls “applied astrobiology”.
No small affair
Astrobiology was invented in the 1990s to provide a unified context for scientific thought about life beyond Earth, whether in the distant past of Mars, or under the icecaps of Jupiter’s and Saturn’s frozen moons, or on the “exoplanets” that had just been discovered around other stars. Because looking for life is an all-or-nothing approach—which had up until that point routinely ended up in the “nothing” camp—astrobiology framed itself instead as a study of the circumstances and contexts in which life might be found, how it might come about and the habitability which might sustain it.
This was a smart scientific move, and also a politically astute one. Astrobiology gave NASA a way to pull together seemingly disparate research interests and align them with a topic that fascinated the public. The space agency’s first orbiting telescope devoted to the study of exoplanets, Kepler, was designed to concentrate on those in the “habitable zones” of stars like the Sun—the region around a star that is neither too close nor too far away for water to remain liquid on its surface. The destinations chosen for NASA’s remarkable Mars rovers, Curiosity and Perseverance, were places which looked as if they might have been habitable in the planet’s distant past, again because of the evidence of ancient water in those places.
Dr Wordsworth’s idea of applied astrobiology, developed at a workshop at Harvard in 2024, takes the idea of focusing on habitability a step further. Astrobiology becomes the context not just for the study of life beyond Earth, but for the study of life from Earth moving beyond its planetary confines: a science not just of studying habitability, but of creating it.
As in the 1990s, the idea has the practical advantage of bringing together areas of study that were previously separate. Space science and human spaceflight have often, in the past, been pitted against each other. As the Harvard workshop’s summary put it, “There are significant benefits to an approach that treats [searching for extraterrestrial life and supporting human life in space] as different aspects of the same essential inquiry.” One benefit is broadening the repertoire of astrobiology. Emphasising the need to make things habitable refashions it into an experimental science.
What might such experiments look like? Showing that it is possible to grow food, or fibres for clothing, in the constraints of a space station or a Moon base would be examples. And as various participants at the Green Mars workshop pointed out, such work would also have the advantage of being economically fulfilling. Keeping a person fed, watered and clothed in orbit currently requires sending up a couple of tonnes of consumables a year, at a cost of around $2m a tonne. With a routine off-Earth population of just ten—seven people on the International Space Station and three on its smaller Chinese counterpart—this is not ruinous, nor is it all that profligate to throw their waste overboard for incineration by re-entry. But in a future world with Moon bases, private space stations and possible missions to Mars the costs begin to mount.
This has spurred a practical interest in growing plants and microbes in space. Mr McCaleb says there are two companies developing systems for doing biological research to be flown on Habitat-1. Erika Alden DeBenedictis, a biologist who runs Pioneer Labs, a biotech company spun off from the Astera Institute, says that the company may well collaborate with such hardware makers as it works on biological systems which can help keep space habitats habitable.
It’s the freakiest show
A longer-term goal is systems that do not just maintain habitability, but embody it. Dr DeBenedictis talks of creating an engineered environment which would not just support life, but which would create the materials needed for its life-supporting capacity to be expanded.
An Earthly example would be the spread of life onto a new, sterile lava flow. Pioneer species of microbes first break down the inorganic surface—what scientists call regolith. Hardy lichen and plants then follow. As life begins to take hold, the processes which turn regolith into soil accelerate. Things produced by life—organic carbon compounds, biologically available forms of nitrogen and the like—make more life possible.
Dr Wordsworth has looked at the possibility of trying something like this out on Mars using “solid-state greenhousing”. The idea is to spread out a layer of material, such as an aerogel, that is transparent to visible sunlight but opaque to both the ultraviolet (which is very intense at the Martian surface) and the thermal infrared parts of the spectrum. The light that came through would warm the regolith below; the insulating properties of the material would stop that warmth dissipating into the thin air. Such layers already occur naturally (though not biologically) in some regions of Mars.
Add such a surface layer to regolith with ice and carbon dioxide frozen into it and you could conceivably get a near-surface habitable zone in which carefully chosen photosynthetic microbes could make a living. If they, or creatures in an ecosystem that was based on them, could also make more materials the greenhouse was made of, you might possibly have a basis for the sort of self-enlarging environment Dr DeBenedictis is imagining.
It is at this sort of point—if not before—that some non-applied astrobiologists, and members of the public, will start to feel concerned. Since humans first ventured into space worries about “planetary protection” have led to procedures meant to stop any life there might be out there from causing problems on Earth and also to stop life from Earth contaminating the environment of living things elsewhere.
There is no evidence of life on Mars at the moment. Nevertheless missions to the planet are diligently scrubbed and sterilised so as to minimise the number of Earthly microbes they take with them, just in case they might do some harm. And the parts of the planet most likely to have some microbial life have been put out of bounds for any missions at all.
The planetary-protection rules formulated by COSPAR, an international scientific body to which national space programmes pay heed, take this approach. At the moment, any bit of Mars which looks unusually habitable is liable to be rated a “special region” for planetary-protection purposes. And sending missions to special regions is not allowed.
A recent report from America’s National Academies on what human astronauts could do to advance astrobiology research on Mars (executive summary: lots) summed up the problem clearly. “[N]ot visiting Special Regions would…minimise or eliminate the chance of finding extant Martian life.” Martian astrobiology thus finds itself in a double bind; the more likely a place looks to support life, the less possible it is to study it.
You do not need to treat the very idea of international authorities with unbridled scorn, as Mr Musk does, to think that this approach needs revisiting. The idea that explorers should operate under such constraints until there is a “definitive answer” to the question of life on Mars today is “totally unrealistic”, says Dr DeBenedictis. Beyond the logical difficulties inherent in proving something’s absence, she points out, there is also the practical issue that, on Earth, finding life in extreme environments is a matter of experiment as much as observation. Scientists take samples from, say, a bit of permafrost, and put them into conditions that might be to life’s liking in order to see if anything responds. Similar approaches will be needed elsewhere. “Terraforming Mars could be reconstrued as the greatest search-for-life experiment you could imagine,” suggests Dr DeBenedictis. “You just heat up the mud ball and see if it turns green, right?”
Experiments with solid-state greenhousing might work to these ends. Edwin Kite, a geoscientist at the University of Chicago who is running a group at the Astera Institute, has a grander warming on offer. Where previous ideas about terraforming Mars focused on adding greenhouse gases to the atmosphere, Dr Kite is exploring the possibility of using solid particles that are far more effective at delivering warming than those greenhouse gases could ever be.
One option would be tiny iron filings optimised to reflect infrared wavelengths; another would be nanoparticles of carbon a single atom thick with similar properties. Models suggest this technology could have truly remarkable power. The average surface temperature of Mars might in principle be raised by 30°C (54°F) or so over the course of a few decades by a system which pumped optimised aerosols into the atmosphere at a rate of just one cubic metre a minute. That level of warming could be enough to thaw out a significant amount of Mars’s frozen water.
Dr Kite is very aware that when models show such dramatic effects it is because lots of things which could go wrong do not. In the models, the particles released at the surface are lifted up high into the atmosphere, stay separate rather than clumping together, spread more or less evenly around the planet and float around for a fair bit of time. None of those conditions may actually hold, and it is to investigate some of them that he wants to fly a “precursor” mission—a lander which releases a few kilos of particles from the Martian surface and tracks their progress.
Such a mission would provide data with more immediate relevance than its implications for the prospects of a deliberate global climate change. Near the surface of Mars the contrast in temperature between the surface (which warms in the sun) and the air above it (which doesn’t) can create intense turbulence: “By some measures…the turbulence is more vigorous than anywhere on Earth,” says Dr Kite.
There is a similar “dual use” aspect to the precursor missions which Dr DeBenedictis says that Pioneer might propose: bioreactors on the surface of Mars that could be loaded with Martian atmosphere and regolith to see how various sorts of microbes fare under such conditions. The main purpose would be to start producing the sort of data which will be needed if astronauts on Mars are to come close to living off the land. But another result would be a new sense of how inhospitable the regolith actually is, and thus what level of effort is really necessary to protect Mars from the scum of the Earth.
Wonder if we’ll ever know
The idea of trying to grow things on Mars just to see if you can is not new. In the late 1990s Chris McKay, a NASA scientist who was an astrobiologist before the term had been invented, suggested a “Mars Biology Demonstrator”: its purpose would be to grow a plant on the planet and send pictures of its progress back home. The idea did not find favour with NASA. But a young South African tech millionaire found it fascinating, and looked into doing it off his own bat. Mr Musk went on to discover that the cost of launching such a mission would be prohibitive, and so decided that he would create a space-launch business instead. At some point the idea of a simple flower on Mars was lost, superseded by the idea of a new branch of humanity.
As yet SpaceX has not concentrated on the biological aspects of putting humans on Mars. Dr DeBenedictis points out that much of the company’s success is based on ruthless prioritisation of the next crucial problem to solve. Paul Wooster, who heads SpaceX’s plans for Mars, says that with large spaceships and smallish crews, early missions will be able to take consumables along with them. It is also the case that building cool new rockets is both closer to the hearts of aerospace engineers and more obviously commercial than the applied biology of Martian agronomy and waste reclamation.
But the technology to put humans on Mars will also allow all sorts of new scientific endeavours there. Astrobiological experiments that apply to the understanding of past and potential future life on Mars will undoubtedly be among them. They will not in themselves lead to self-sufficient colonies, let alone terraforming. But they will expand human understanding of life in a cosmic context. And that will be a reward in itself.
Correction (January 5th 2026): An earlier version of this story referred to Vast’s “Haven-1” space station as “Habitat-1”. We regret the error.
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