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This is an Arabidopsis plant cultivated in lunar soil (yes, soil sourced from the moon!) after about two weeks of growth. Image courtesy of Tyler Jones, UF/IFAS.It's now confirmed—moon soil (lunar regolith) can indeed support plant growth. Interestingly, plants grown in younger lunar soil experience less stress compared to those cultivated in older soil.
The groundbreaking findings, published on May 12 in the journal Communications Biology, are vital in exploring how future moon settlers might grow their own food and generate oxygen through lunar agriculture. These experiments represent the first attempts to cultivate plants in actual lunar regolith rather than in simulant soil.
"It's great news that plants can grow in lunar soil," said Robert Ferl, a space biologist at the University of Florida and co-author of the study, during a press briefing on May 11. The challenges faced by the plants demonstrate that there is much to learn about lunar biology and the chemical interactions of moon soil. However, the key takeaway is that until this experiment, no one was sure if plants, particularly their roots, could thrive in the sharp, hostile environment of lunar regolith."
Lunar Soil Presents Stressful Conditions
The team planted thale cress (Arabidopsis thaliana) seeds in small amounts of lunar regolith collected from the Apollo 11, 12, and 17 landing sites, as well as in lunar soil simulant. Arabidopsis, a plant closely related to mustards, cauliflower, broccoli, kale, and turnips, has been cultivated in various soils and environments, including space.
"It’s edible, though not particularly flavorful," said Anna-Lisa Paul, the lead author and plant biologist. "By studying Arabidopsis, we gain valuable insights that can be applied to crop plants."
Additionally, Arabidopsis plants are small and complete their growth cycle in about a month, making them ideal for growing in just a teaspoon of lunar regolith.
The researchers discovered that all three lunar soils were able to support plant growth, albeit with some challenges. When compared to control plants grown in lunar simulant soil, those cultivated in actual lunar regolith had smaller root systems, slower growth, less developed leaf canopies, and displayed stress indicators such as darker green or purple-colored leaves.
By the 16th day, visible differences were evident between plants cultivated in lunar simulant (left) and those grown in lunar soil (right). Image by Tyler Jones, UF/IFAS.Variations Across Lunar Sites
While all plants grown in lunar soil showed signs of stress, the degree of stress varied. The plants in Apollo 11 regolith experienced the most stress, whereas those in Apollo 17 regolith were the least affected.
Although Apollo 11, Apollo 12, and Apollo 17 all landed in the basaltic mare regions of the moon, there were notable differences between the sites. The regolith at the Apollo 11 site is considered the most mature of the three, having been exposed to the lunar surface the longest. This exposure has caused the soil to weather from the effects of solar wind, cosmic rays, and micrometeorite impacts. These processes have altered the regolith’s chemistry, granularity, and glass content. While all three sites have undergone similar processes, Apollo 17 has experienced the least maturation.
After 20 days of plant growth, the research team conducted gene analysis and found that plants grown in lunar regolith exhibited stress responses related to salt, metals, and reactive oxygen species. These results suggested that much of the plants' difficulties stemmed from the chemical differences between lunar regolith and lunar soil simulant, such as the oxidation state of iron.
Lunar iron tends to exist in an ionized metallic form, while simulants and Earth soils generally contain iron oxides that are easier for plants to access. Ionized iron results from interactions with the solar wind, which explains why the most mature soil, that from Apollo 11, resulted in the most stressed plants.
"Simulants are extremely useful for engineering purposes, such as determining whether a rover will get stuck in the soil," said co-author Stephen Elardo, a planetary geochemist at the University of Florida. "But when it comes to the chemistry that plants interact with, they are not a perfect match. The devil is in the details, and ultimately, it's the details that matter for the plants."
Robert Ferl, a space biologist and co-author of the study, is pictured here weighing out small amounts of lunar soil samples collected during the Apollo missions.Select Your Resources Carefully
The findings confirm that lunar regolith is capable of sustaining plant growth, a crucial component for any long-term lunar base. Plants will play vital roles in water recycling, removing carbon dioxide, and producing oxygen, food, and essential nutrients.
"This experiment is well-structured and carefully designed to test plant growth on genuine lunar regolith samples returned from Apollo missions 11, 12, and 17," said Edward Guinan, an astronomer from Villanova University, Pennsylvania, who has previously worked with moon and Mars soil simulants. "As the researchers note, the plants are stressed and do not thrive. They show characteristics similar to plants grown in salty or metal-laden soils. It may be worthwhile to experiment with other terrestrial plants that can tolerate poor or salty soils. Guinan was not involved in this study."
This research also highlights that while plants can be cultivated using lunar resources, the origin of these resources will significantly influence their growth success.
No matter where future lunar explorers decide to establish their habitat, "we have the power to select the source of materials for use in creating growth habitats," Paul explained. "The key factor is not where the habitat itself is located, but where the materials are extracted from."
Kimberly M. S. Cartier is an experienced senior science reporter at Eos.org. Holding a Ph.D. in extrasolar planets, she reports on space science, climate change, and issues related to STEM diversity, justice, and education.
This article is shared with permission from Eos, under a Creative Commons license. You can access the original article here.
