Elon Musk might have his sights set on settling Mars, but recent experiments that utilized extraterrestrial soil suggest human settlements could have a far easier time on the moon.
Scientists have come up with many ideas for growing food in outer space. One concerns growing plants directly in water (called hydroponics), for instance, and another is growing them using misted nutrients from the air (called aeroponics). But both of these options are expensive, so some scientists are also exploring a more traditional method of feeding future astronauts — growing crops directly in lunar and Martian soil.
Soil samples from the moon taken during the Apollo missions have been contaminated with moisture, and collecting new samples would be too costly, so for the moon experiments, the scientists made do with artificial soil reconstructed by Exolith Lab and based on samples taken during the Apollo 16 mission in 1972. Reconstructed Mars samples (humans are still yet to return any true Mars samples from the Red Planet) were based on data collected by the Curiosity Rover, which is currently roaming the Martian landscape. (Soil, in this case, is used loosely because lunar “soil,” or more accurately “regolith,” as well as Martian regolith differs considerably from what we traditionally call “soil” on Earth).
“The interesting thing is that the lunar crops grew better than the Martian ones,” said Laura Lee, a graduate research assistant at Northern Arizona University who presented the research poster at the 2024 American Geophysical Union, speaking to Space.com. “We had thought that it would be the other way around.”
The ground on Mars is full of nitrogen, a vital component for planet life, raising hopes that it might be more hospitable than it appears — but Martian soil is also dense and clay-like, the researchers realized, restricting the amount of oxygen available to plant roots.
The science team tried growing the crops with Milorganite, a brand of fertilizer made of heat-treated microbes that digest wastewater, which was thought to be a good candidate for producing crops in space settlements. Waste disposal would be a problem for any off-world settlement, and researchers have long wondered if the wastewater from astronauts could be used to fertilize crops and sustain farming without importing fertilizer from the Earth — solving two potential problems at the same time.
But although the study has not yet been published, preliminary results suggest that recycling waste from humans on the moon and Mars might not be a straightforward solution. Martian corn grown with wastewater-digesting bacteria had a survival rate of 33.3%, whereas corn grown in pure nitrogen fertilizer — which is more regularly used for crops on Earth — had a survival rate of 58.8%, suggesting that fertilizer might need to be imported to make up for low yields if we go the human-wastewater-fertilization route.
The researchers are now testing broccoli, squash, beans and alfalfa with different mixes of regolith and fertilizer in both soil types to see if these plants respond better than the corn did. Alfalfa responded positively to both lunar and Martian soil — and there’s some evidence it could also be used as a future fertilizer of outer-space crops. The scientists have yet to test potatoes, which notably fed the protagonist of science fiction novel and movie “The Martian,” which won critical acclaim for its realistic depiction of an astronaut forced to survive by growing his own food on a Martian space base.
Before Mars could become self-sufficient, however, massive amounts of imported food would be needed in the interim, according to the authors of a 2019 paper published in the New Journal discussing the development of a Martian settlement. And, even if successful, crops on the Red Planet would have to be grown alongside closed-off human settlements without an atmosphere, similar to how plants are grown on the International Space Station.
Martian greenhouses would have to account for low temperatures, high radiation, and a complete lack of decomposed organic matter that enables plant growth on Earth. Martian soil is also full of perchlorates, a toxic chemical that would need to be removed.
The AGU research drives home the challenges of sustaining agriculture on Mars even when compared to the moon, the latter of which is a much shorter distance for food transportation. The 2019 study found it would take roughly 100 years for Mars to become self-sufficient, whereas NASA studies suggest that a lunar settlement could reach that point in decades.
But life on the moon comes with plenty of problems, too. The moon has no atmosphere, which leaves it vulnerable to the impact of smaller asteroids that would burn up before reaching the surface of most planets. Because of its weaker gravity, the dust kicked up by the asteroid impacts doesn’t settle, floating around and threatening to clog up any machinery that might be needed to help plants grow. The crops would also have to be well-shielded from solar radiation, which is less of a problem on Mars.
The moon’s lack of atmosphere makes it unlikely that humans could ever live on its surface without spacesuits and protective bunker-like buildings, but Mars might be different. The Astera Institute and Pioneer Labs ran a workshop at AGU on the feasibility of terraforming Mars, investigating how warming the planet’s surface could enable human habitats in less than a century.
Creating Martian global warming
The plan involves sending photosynthetic bacteria to Mars and artificially warming up the planet in the hopes of creating an oxygen-rich atmosphere to enable plant growth. The scientists discussed pioneer species — like moss, mold and lichens — which could be introduced to Mars and set the stage for terraforming the planet.
“Global warming has proven that humans are capable of altering planetary climates and has prompted the development of climate engineering technologies that are nearing deployment on Earth,” said the authors in the Mars Terraforming Workshop Proceedings. It’s unclear how Mars would look after such a transformation — it could lose its iconic blue sunsets, for example.
In 1971, astronomer Carl Sagan suggested melting Mars’ ice-covered lakes at the polar regions to warm the planet, which could provide nutrients and water to plants during seasonal ice melt as the planet slowly warms. Still, scientists disagree over whether melting the ice would release trapped carbon dioxide, which could add to atmospheric pressure.
Because Martian regolith doesn’t clump like soil, there’s also a risk that the melting ice could drain and form water aquifers, which would not sustain much above-ground plant life desirable for humans.
Warming Mars could cost approximately $1 billion per year, which the researchers estimated could effectively heat up the red planet by one degree Celsius annually — with the aim of reaching around 30°C to enable comfortable plant growth. Yet, the scientists said the plan is cheaper than any existing alternatives.
The document assessed other ideas for terraforming Mars such as using sun reflectors to heat the planet or warming it with nuclear warheads, an idea that would require “exploding the equivalent of the entire U.S. arsenal every two minutes to sustain a warm Mars,” which the missive called “not necessary.”
The extent to which life exists or used to exist on Mars, as suggested by limited evidence of fossilized bacteria, would serve as a guide on how humans should influence the Martian biosphere, the scientists said. Put simply, thawing the ice on Mars could reactivate life that once existed there.
“The question of whether Mars hosts extant life remains one of the most intriguing yet unresolved questions in astrobiology,” said the scientists. But we may never find the answer, they concluded, as “it is impossible to prove that something does not exist.”
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