A century from now, people on Mars might stroll through forests filled with juniper trees, kudzu vines, and heath shrubs. Maybe.
Ecologist Paul Smith of the University of Bristol suggests that long-term residents of Mars, whether they’re settlers or astronauts at research outposts, could build small nature preserves, shielded from the harsh Martian environment by clear domes or layers of Martian crust. But they’re not going to look quite like any forest on Earth.
He published his proposal in the Journal of Astrobiology.
What’s new — Smith proposes that once humans have established a solid presence on Mars, they’re likely to want a small piece of home, partly to provide some fresh food and produce oxygen, but also to enable people to do the Martian version of going outside to touch some grass. He suggests about 20 hectares of forest park, carefully contained under protective pressurized domes or sheltered in lava tubes lit by mirrors and fiber optics.
These hypothetical nature preserves won’t be able to replicate any of Earth’s forests, however; even with help from 22nd-century engineers, the Martian environment will be a bizarre place to try and plant a forest. The best option, says Smith, will be to throw in as many species as possible and let evolution select the combination that works best. And the result may include some combinations that would never happen naturally on Earth.
“They will be recognizable, and they will have a similarity to ecosystems that we find on Earth, but they will not be exactly the same,” Smith tells Inverse.
How it works — On Earth, nature preserves usually require not much more than legislation and signs, but on Mars, they’ll need shielding against ultraviolet light and cosmic rays, pressurized air, artificial heating, a lot of added water, and some way to get toxic chemicals like perchlorates out of the regolith. One option might be a clear dome, pressurized on the inside and engineered to block harmful wavelengths of UV light while admitting the ones plants need for photosynthesis. Another might be a lava tube, putting several meters of Martian rock and regolith between the park and incoming cosmic rays; sunlight could be delivered by a system of mirrors (remember that one scene in The Mummy?) or fiber optics.
An elecromagnetic shield could block cosmic rays, exactly the way Earth’s magnetic field repels most of them away from our planet. On the other hand, patches of the Martian crust still have their own small, local magnetic fields. If future missions build their nature preserves in the right spot, the planet itself could protect them. Maintaining air pressure might be much easier at the bottom of a deep crater — like the Hellas Basin, where the nature air pressure is about 12.4 millibars higher than outside.
Either way, airlocks would let visitors stroll in and out, leaving behind the arid, dusty Martian desert for a lush green forest.
“Mars’ forests would not resemble or function exactly like Earth’s forests but could still deliver wonder,” writes Smith in his paper.
Digging into the details — There’s no way to predict which species would thrive in one of Smith’s giant Martian terrariums, or in what combination. After all, ecologists don’t yet fully understand the complex network of relationships between plants, animals, fungi, and microbes that make our familiar Earth forests work. The best option, then, is to send a selection of plants, fungi, and insects that do well in dry, cold, or high-altitude environments here on Earth, and let evolution take its course.
“We do understand that ecosystems will spontaneously self-assemble if you deliver enough species to a particular site,” Smith tells Inverse, and they will assemble in ways that we will not necessarily foresee.”
The process will probably start with microbes. Cyanobacteria could fix nutrients in the regolith in a form plants can use, and they also produce oxygen and make the soil better at holding water. Other bacteria can even break down the deadly perchlorates.
According to Smith, the upper layers of the forest are likely to include a lot of hardy high-altitude and high-latitude conifers like juniper, along with pine and birch. Beneath that canopy, shrubs like heath — many species of which grow in South Africa — might play a role, along with herbs like cicely, which is native to southern Europe and has a sweet, anise-like scent. But one surprising inclusion is kudzu, a vine native to southern Asia — and an unstoppable, all-consuming invasive menace in the southeastern United States.
“It's a survivor. It's a great survivor,” says Smith. “It's also a very useful plant.” Among more tangible uses, like making rope, kudzu also fixes nitrogen in the soil — something other plants will find very helpful — and exhales oxygen in a form called ozone. If kudzu breathes enough ozone into the Martian atmosphere, or at least the contained atmosphere of a domed nature preserve, that could help protect the forest against incoming radiation.
Invasiveness, after all, is a matter of context.
Fungi and insects will also have important roles to play, but there’s one thing you won’t find in Smith’s hypothetical Martian forest: wildlife. Here on Earth, animals like deer, rabbits, and mountain lions can come and go as they please from nature preserves. Under a protective plexiglass dome on Mars, however, resident wildlife would be trapped in a park too small for them to range as they would in the wild. And, of course, there’s the ever-present risk of the dome losing pressure, and Smith says it would be unethical to trap larger animals in that situation.
Why it matters — A forest is a tremendously useful no matter what planet you’re on. Forests can provide food, building material, and even raw ingredients for medicines. They also turn carbon dioxide into oxygen, which is something people living in an enclosed habitat might find especially helpful. But Smith emphasizes the mental health benefits of a nature preserve, especially one with big, charismatic vegetation like a forest, for humans stationed far from home on an alien world.
“There's a fair bit of information in the published literature which says that astronauts get a lot of benefits from even interacting with the plants that they have on the [International] Space Station, for instance,” he says. And a forest “gives people a sense of escape, as a vegetation that you can enter.”
Astrobiologist Jim Kasting of Pennsylvania State University, whose work focuses on searching for habitable planets, is skeptical, however. “It would also cost an arm and a leg to assemble this thing on Mars,” he tells Inverse. “I think the psychological benefit you get out of having all these trees and Earth-like biome on Mars does not justify the cost.”
What’s next — Early Mars colonies will probably bring plants with them, the author says. And at some stage, they’ll probably establish greenhouses to grow food and help with other tasks like water purification and oxygen.
Astrobiologist Chris McKay tells Inverse the idea is “probably the most complete study of what comes after a first human base on Mars, which might have a small greenhouse for food production, and before attempts to fully terraform Mars.”
“It is a long way from terraforming the planet,” McKay adds.
But how long will it take to get there? That mostly depends on how long it takes humans to gain a foothold on Mars, and on how long it takes to develop technological answers to the problems of how to shield a 20-hectare patch of Martian surface from cosmic rays while also letting in sunlight and keeping the whole thing warm, watered, and pressurized.
“Figures for terraforming Mars talk about centuries up to hundreds of thousands of years,” says Smith. “These contained environments are something we can achieve very much sooner.” He estimates that “if we have a smooth ride,” the idea of contained nature preserves on Mars could be viable in roughly a century.
Meanwhile, the first people on Mars will inevitably bring other organisms with them: their own microbiomes, if nothing else, but probably also at least a few plants for science experiments. And that, says Smith, is important.
“We will not travel alone because we did not evolve in isolation,” writes Smith.