For the first time ever, scientists have grown plants in lunar soil returned from the Apollo missions. But given the degree of stress seen in these plants, it’s unlikely we’ll be farming on the Moon anytime soon.
New research in Communications Biology is the first to show that plants, specifically thale cress (Arabidopsis thaliana), will grow in lunar regolith.
“Think about that for a minute and the implications are astounding,” the three scientists behind the study, all from the University of Florida, wrote to me in a group email. “Terrestrial life can potentially live on the Moon, and for astronauts spending any time on the Moon, plants can be used for life support in ways that have only been speculated about.”
No doubt, this represents a truly astounding and unexpected result. As the scientists explained, lunar regolith is nothing like the soils found on Earth, the former being sharp, abrasive, and with no organic elements whatsoever. What’s more, lunar regolith involves certain chemical states, like those having to do with iron, that aren’t present in terrestrial soils. They’re also packed with tiny shards of volcanic glass. And of course, the Moon, with its paltry atmosphere, is continuously bombarded with radiation.
Yes, the plants grew, but that’s not to say they did fantastically well. The thale cress specimens grown in the lunar regolith showed signs of stress, including slow growth, low volume, and discoloration. The team, which included horticulturist Robert Ferl from the UF Institute of Food and Agricultural Sciences, says more research will be needed should we ever hope to grow plants on the Moon using locally sourced soils. Horticulturist Anna-Lisa Paul and geologist Stephen Elardo, both from UF, are co-authors of the study.
That we would want to grow plants on the Moon is understandable. Plants produce oxygen and starch while absorbing carbon dioxide and recycling water. They “complete the sustained life support cycle here on Earth and will likely do the same when we move off the Earth,” the researchers explained.
For the study, they used samples brought back from the Apollo 11, 12, and 17 missions. It was not easy for them to get ahold of these precious materials. The team made three formal requests for the samples over the past 11 years, with NASA finally obliging and loaning them 12 grams for the experiment. That’s just a few teaspoons. Working with simulated lunar soil, the scientists spent years trying to figure out the minimum amount needed to run this experiment. A lunar simulant known as JSC-1A, which the team later used as a control substrate for the experiment, was key to this process.
“Once we knew the minimum we could work with, one gram per plant, we knew how much to ask for,” the team told me. “In order to make the study statistically robust, we needed four plants per lunar sample. That formed the basis of our request to NASA for samples. ”
Importantly, not all of the Apollo samples were equal. The Apollo 11 samples were taken directly from the surface and are considered “mature soils,” as they’ve been exposed and churned by cosmic winds. By comparison, the samples from Apollo 12 and 17 were dug from deeper layers. In addition to the JSC-1A lunar simulant, the researchers attempted to grow plants in volcanic ash from Earth, which also served as a control substrate.
The scientists used thale cress — a small flowering plant native to Eurasia and Africa — because its “genome has been sequenced and well mapped with respect to the function of most of its genes,” the scientists said. This allowed them to spot the specific genes used by the plant to physiologically adapt to growth in the lunar regolith. And because thale cress is so tiny, they were able to grow the plants in a single gram of material, placed inside thimble-sized wells normally used to culture cells.
Incredibly, the thale cress grew in all soil conditions tested, albeit more slowly in the lunar regolith. It also took longer for the Moon plants to grow larger leaves, and their root systems were stunted compared to the controls. These were taken as signs of stress, as were the reddish-black pigments observed on the plants.
The scientists also observed the rates at which the plants expressed genes related to stress, such as responses to metals and reactive oxygen-containing compounds. The plants in the Apollo 11 substrate produced 465 of these genes, while the Apollo 12 plants produced 265 and the Apollo 17 plant 113. This finding suggests regolith sourced at the surface is less ideal as a growth substrate compared to soils found deeper below. The scientists say prolonged exposure to cosmic rays and solar wind, and also the presence of small iron particles, likely induced the stress observed in the experiments.
I asked the team about possible mitigation strategies to treat the lunar regolith such that it can properly sustain plant life.
“Ahhh, a very important question,” they responded. “Our study suggests that some mitigations might be needed for really good growth. Some of that mitigation may occur by repeatedly growing plants in the same sample, letting the biology condition the soil. Other more active mitigations, like cycling water through the regolith, could work as well. ”
A key goal of NASA’s upcoming Artemis program is to build a sustainable presence on the Moon. The new paper, with its remarkable findings, sets us in the right direction toward making this happen.