Astrobiology students cultivated leafy greens, sweet potatoes, and even hops in simulated Martian dirt.
NASA and private entrepreneurs are pushing to land people on Mars within the next generation. To survive on Mars, colonists will need a lot of gear, not least of which is food. Since lugging food adds a lot of weight to spacecraft — and packaged food only retains its nutrients for so long, anyway — any would-be Martians will need to grow food on site in order to survive.
But conditions on the Red Planet are different than on Earth. The surface receives less than half the amount of sunlight that Earth does, and dust in the atmosphere can attenuate it even more. Due to the absence of an ozone layer, more ultraviolet radiation reaches the ground. As to the Martian surface itself, the dirt (technically “regolith”) is more iron-rich, particularly in iron oxides.
To see how terrestrial plants might fare in Martian soil, students at Villanova University last semester conducted the Red Thumbs Mars Garden Project. They obtained simulated Martian soil, made from volcanic basalts similar to those on Mars, and mixed it with other compounds to make it about 90% similar to Martian regolith.
The students focused on nutritious plants, including lettuce, kale, garlic, and potatoes, as well as hops (the business students were looking for inventive ways to make Martian greenhouse products marketable, professor Edward Guinan quipped during his talk January 12th at the American Astronomical Society meeting in Washington, D.C.). They then planted the seedlings in different concentrations of Martian soil in a campus greenhouse rigged for light levels on the Red Planet and let things unfold.
Despite hiccups in the pilot study (lack of greenhouse temperature control, students forgetting to water plants), several of the experimental foodstuffs grew fine in the Martian simulated dirt. Mixed greens such as lettuce and kale did well, but potatoes — the mainstay of protagonist Mark Watney in The Martian — did not. The clay-like Martian simulant was so thick that it crushed the growing taters, giving them no room to expand.
Overall, plants did much better when the students added filler such as coffee grounds to the Martian simulant, Guinan says. The filler fluffed the dirt up enough that water could percolate through and reach the roots.
One major difference between the Villanova project and real Martian soil is perchlorate (CClO4). Perchlorates abound in the uppermost layer of Martian regolith, potentially lowering the freezing temperature of water enough to explain some fleeting signs of liquid water activity on Mars.
But perchlorate is toxic to humans, causing thyroid problems and even death. Humans on the Red Planet might breathe it in from dust that infiltrated habitats, and growing food with it would be dangerous. “Matt Damon would have died,” Guinan said, referring to the Hollywood version of the novel. “It was never mentioned in the movie, you know — you don’t want to talk about things like that.”
Farmers on Mars will need to remove any perchlorate from the Martian soil before using it. One way is to rinse the soil, since perchlorate dissolves in water. Another, more enticing way is to use perchlorate-eating bacteria, which produce oxygen as a metabolic byproduct. That might protect the colonists from serious health problems while also bolstering their breathable air supply.
For those interested in doing similar projects with their students, Guinan recommends lettuce. “It grows fast, and you can eat it,” he says. “I ate the lettuce. I’m still here.”