The Apollo astronauts faced a lot of challenges in their time on the moon, but having enough to eat was not among them. The longest any of the crews spent on the surface was the three days logged by Apollo 17 in 1972, and even in the astronauts’ tiny lunar module, there was enough room for the shrink-wrapped, pre-packaged provisions they’d need for such a brief camping trip. The next time around, though, things will be different.
As part of NASA’s Artemis program, which aims to return American astronauts to the moon after a half-century hiatus, crews won’t be coming just to visit, but to stay, establishing a long-term presence in permanent lunar bases. That means not carrying all of the crews’ food along, but growing at least some of it on-site—using the moon’s regolith, or soil, itself as a growth medium inside lunar greenhouses.
The question, though, is whether the dry, sharp, glassy, soil, bathed for epochs by cosmic radiation and solar wind, can support plant growth anything like the rich, loamy soil of Earth. The answer, according to a new study published in Communications Biology, is maybe. For the first time, researchers attempted to grow plants in lunar soil brought back by the Apollo crews. And it turns out that success depends on where exactly on the moon you do your planting.
The concept of extraterrestrial farming was widely popularized in Andy Weir’s book The Martian, in which a marooned astronaut grows potatoes in Martian soil, using human waste as a fertilizer—but Weir is by no means the first person to come up with the idea of tilling alien soil.
“This concept of growing crops and other plants in soil or regolith from the moon or from Mars has been around longer than I’ve been alive, so it’s hardly a new concept,” he tells TIME. Maybe not, but until now, the idea had never been attempted.
The new research, carried out by a team of two horticulturists and one geologist from the University of Florida, was a long time in the making. The scientists applied to NASA three times over the past 11 years for small samples of soil brought back by some or all of the six Apollo landing missions. They were refused twice. It was not until the third time, about 18 months ago, that the space agency finally agreed.
“With NASA prepping themselves to go back to the moon for longer excursions, it became much more relevant that we understand how resources that are in situ on the moon can be used to further exploration,” said horticulturist and lead author of the paper Anna-Lisa Paul, at a May 11 press conference announcing the release of the results.
Still, the space agency did not turn over much of its soil. All told, NASA agreed to lend the researchers just a collective 12 gm (0.42 oz) of soil, gathered by the crews of Apollos 11, 12, and 17. The six Apollo landing missions brought back a total of just 382 kg (842 lb.) of lunar rocks and soil—which sounds like a lot but actually makes the material exceedingly rare. “These samples are precious natural treasures,” said Paul.
Their small sample made for a decidedly modest crop. The researchers did their planting in plastic plates with thimble-sized wells that are more commonly used to grow cell cultures. Each well got a gram of soil—or about a teaspoon—with four wells apiece for each of the three Apollo missions. A final four wells were filled with a simulated lunar soil made mostly of fine, earthly volcanic ash, to be used as a control. The plant the researchers chose was the thale cress (Arabidopsis thaliana), selected both because of its hardiness and because its genome has been fully sequenced.
“We know an awful lot about this plant from every nucleotide in its genome to what genes are expressed in different nutrient conditions,” said horticulturist and co-author Rob Ferl at the press event. “So there’s a huge database.” That basic knowledge would make it possible to determine exactly what was allowing the plant to thrive—or preventing it from doing so—within the medium of the lunar soil.
Once the seeds were sown, the plants were irrigated and placed in clear, ventilated terrarium boxes under growth lights. Within 48 to 60 hours, all of the seeds in all of the mini-pots began to germinate—but with very different results depending upon the soil used.
Far and away, the best results were obtained in the terrestrial volcanic soil, with the plants sprouting quickly and growing broad, healthy leaves. The seeds grown in the lunar soil were a very different matter. While all of them did sprout and all of the root systems grew to fill their tiny wells, on the whole, the plants were smaller and grew more slowly than the control plants. Many of the leaves also exhibited black and red discoloration indicative of metabolic stress and overall ill-health.
In general, it was the Apollo 11 plants that grew the most poorly, followed by Apollo 12 and finally Apollo 17, which, relatively speaking, produced a bumper crop of Arabidopsis thaliana. The reason, the researchers concluded, has to do with the age of the soil. The older—or more mature—lunar regolith is, the longer it’s been exposed to cosmic energy and solar wind, and the greater the micrometeorite bombardment is that produces the glassy shards in the soil.
Apollo 11’s Sea of Tranquility site is older geologically speaking than Apollo 12’s Ocean of Storms soil, which experienced more-recent lava flows than Tranquility. And both are more mature than Apollo 17’s Taurus-Littrow site, a mountainous region whose surface was shaped by meteorite and asteroid bombardment more recently in geological time.
“What we found was that the regoliths that were more mature were indeed more toxic to the plants, or at least they presented a more toxic response,” said Paul.
Genetic studies of the plants proved that point further. Over 1,000 genes in the Arabidopsis thaliana can be activated to help the plant respond to stress. In the Apollo 11 samples, 465 such genes responded to the challenges posed by the alien soil. For Apollos 12 and 17, the numbers were 235 and 113 respectively. In other words, the thale cress’s DNA had to fight harder to adapt to the foreign soil gathered during the Apollo 11 mission. That’s bad news for future farming in the Sea of Tranquility, the Ocean of Storms, and even Taurus-Littrow, but potentially good news for future lunar crews overall.
“What we could simply do in the absence of other constraining factors, is land and establish a habitat on a lunar surface that is significantly younger than the Apollo 11, 12, and 17 sites,” said geologist and co-author Stephen Elardo. Sites covered by immature lava flows would be especially promising, says Elardo. “If you look at lava flow areas here on Earth—look at Hawaii for example, look at Iceland—those areas are quite green.”
So does this mean a future in which astronauts can indeed live off the lunar land? Weir, for one, thinks so. “If you’re talking about a further future where you have actual lunar colonists, then I would say yes, because shipping food there is prohibitively expensive,” he says.
Lunar agriculture of course, must await lunar landings, and with the Artemis program nowhere near ready to meet its original goal of having boots back on the moon by 2024, the most that NASA can promise is that the missions will fly sometime in this decade. Whenever that promise is fulfilled, the new study does bring the future explorers one small step closer to being able not just to visit the moon, but to call it home.
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