Scientists grow plants in lunar soil – and find bad news

The good news for proponents of space colonization is that scientists have shown you can grow plants in Moon dirt. But the bad news for anyone envisioning a lushly verdant lunar astronaut salad bar is that plants grown in lunar regolith don’t grow very well and are generally stressed out by the experience.

In a new study published Thursday in the journal Communications Biology, researchers at the University of Florida grew plants in lunar regolith from Nasa’s Apollo missions for the first time, comparing their growth to that of plants seeded in terrestrial volcanic ash.

The lackluster performance of the plants grown in the Apollo samples presents a challenge for proponents of in “situ resources utilization,” the term for astronauts creating their water, oxygen, fuel, or in this case, food, from resources found on an extraplanetary body rather than pack them from home.

The researchers seeded Arabidopsis thaliana, a small flowering plant more commonly known as thale cress, either in samples of lunar regolith brought back to Earth by the Apollo 11, 12, and 17 missions, or in a volcanic ash-based control soil designed to mimic lunar regolith. The plants seeded into the Moon samples grew slower, smaller, and showed more signs of stress such as pigmentation and the expression of stress-related genes, than those grown in the volcanic ash.

And while the plants grown in volcanic ash developed more or less uniformly, the plants grown in the Apollo 11 samples fared worse than the plants in the Apollo 12 and 17 samples, suggesting variability in the samples. The Apollo 11 sample, for instance, was exposed to solar and cosmic radiation the longest, and the researchers theorize the effects of that long-term energetic bombardment could have left the lunar regolith particularly reactive to biology.

The study is the first to attempt growing plants in lunar regolith as the primary growth medium, and the results contrast with those of experiments conducted in the 1970s.

During the Apollo program, researchers crumbled lunar regolith, giving plants growing in terrestrial soil a veneer of Moon dust, and found the plants actually thrived compared to controls. The experiments were mainly focused on ensuring no unknown pathogens or toxins lurked in the Moon samples astronauts brought back, and researchers believed the additional nutrients were responsible for the plants’ growth.

Seeds taken to the Moon by Apollo astronauts and returned to Earth were then planted, with many successfully growing into mature “Moon trees,” but the experiment addressed the viability of seeds taken to space, not seeds in soil from space.

More recently, in 2019, an experiment on China’s Chang’e 4 lunar lander successfully germinated seeds on the Moon for the first time, but did so in a sealed container using Earthly soil

The current study’s takeaway is that growing crops on the Moon will not be as easy as simply putting up a pressurized greenhouse and planting seeds. As with other experiments with in situ resource utilization, more research is needed.

Space agencies like Nasa and the European Space Agency are currently researching many different technologies for utilizing resources found in space so that astronauts do not have to pack everything they need with them from Earth. Esa scientists are studying how to extract oxygen from molten lunar regolith, for instance, while an experimental device on Nasa’s Perseverance Mars rover is extracting oxygen from the Red Planet’s thin atmosphere.

Nasa plans to return to the Moon in 2025 as part of the space agency’s Artemis program, which aims to use the Moon as a practice zone before a mission to Mars in the early 2040s. Astronauts spending weeks or months on the Moon will have ample opportunity to experiment with in situ resource utilization, including ways of modifying lunar regolith to be more friendly to plants.

And it could take a lot of experimentation, according to the present study’s authors.

“Further characterization and optimization would be required before regolith can be considered a routine in situ resource, particularly in locations where the regolith is highly mature,” they wrote in the paper.