The space race of the 21st century keeps pushing the boundaries of researchers and engineers, aiming to bring humanity closer to commercial space travel and colonization of other planets. Besides developing and optimizing aircraft technology and other machinery necessary for venturing into the final frontier, researchers are also exploring the strategies for producing food in outer space to reduce the need for supplies from Earth. And is there a better place to start than the Moon?
The six Apollo missions that took place from 1969 to 1972 brought 842 pounds of lunar regolith back to Earth for further study. Since then, the regolith was used sparingly, most of it being carefully stored for important future research. Only half a century after the Apollo missions, commercial space travel and colonization of other planets had left the realm of imagination to become a tangible goal. And so, NASA decided to reopen the storage, take some moon dust and start testing. In collaboration with researchers from the University of Florida, they performed experiments to determine if plants can grow in lunar soil. The results were nothing short of fascinating.
Going beyond the realms of Earth and staying there for a while necessitates reliable sources of water, oxygen, and food. Plants can take care of the latter two – if we find a way to grow them in space. Scientists have been exploring the solution to this problem for decades, attempting to prepare humanity for the impeding Mars colonization. However, all of the previous studies investigated hydroponics as the primary growing system. Hydroponics seemed to be a more reliable system, as it is easier to replicate the conditions on Earth. And more importantly, uncontaminated space rock samples are not very abundant here on Earth, making experiments with adequate solid substrates out of reach. That was, until this year.
For the first time in human history, researchers from NASA and the University of Florida tested the viability of lunar regolith as a plant substrate. They tested three types of lunar regolith, brought during Apollo 11, Apollo 12, and Apollo 17 missions. The types of regolith differed in their maturity and chemical content. The more mature ones were longer exposed to cosmic rays and have higher iron content. The control of the test was a lunar simulant made of basaltic ash. To mimic the conceivable conditions of cultivation on the Moon, they grew the plants in terrarium boxes under grow lights.
The researchers allotted 900 mg of lunar regolith for each type of regolith. The regolith was ground into small particles (<1 mm), and a nutrient solution was added before the seeds of thale cress were sown. Thale cress (Arabidopsis thaliana) was the plant of choice for the experiment, being the standard model organism in plant biology. The seeds were placed directly in the treated regolith to make full contact with the volume and left to germinate. Assessment of the sprouted plants included measuring their morphological and physiological properties and gene activation.
A few days after the sowing, the researchers could see the sprouts emerging – all of them. To their even greater surprise, the sprouts in all samples looked the same until day 6. After that, the sprouts grown in the lunar regolith started showing stunted growth and slower development compared to the control. Many plants also developed intense pigmentation, which indicates exposure to stress. Gene expression tests confirmed activation of a wide variety of stress-related genes, primarily ones related to salt, metal, and reactive oxygen species exposure.
All plants grown in lunar regolith were visibly stunted compared to the ones grown in lunar simulant control. However, differences were also visible between the three types of regolith. Regolith samples from the Apollo 11 mission were the least accommodating for plant growth, with plants in the samples showing very severe symptoms of stress. The samples from Apollo 12 were a bit more lively, while the Apollo 17 samples fared the best. Some of the seedlings grown in the Apollo 17 regolith were almost as successful as the plants in the control group. This indicates that regolith maturity plays an important role, with more mature regoliths being less favorable.
The results of the study led the researchers to an incredible conclusion – plants can indeed grow in the lunar regolith. Although it has far less favorable qualities compared to almost any soil here on Earth, lunar regolith does hold the potential to become a viable substrate for growing plants on lunar bases in the future. Scientists now have a better idea about the possible directions of development in this area and will continue to investigate how to transform the regolith into a viable plant substrate.
These studies will not only help establish lunar bases but also teach us how to transform barren, infertile soils on Earth into arable land. Such knowledge can greatly contribute to securing food production, currently threatened by climate change and pollution. There is a great number of limitations to overcome until lunar gardens become a reality, but with the ever-growing knowledge and curiosity of humankind, those great feats are becoming more palpable.
- Scientists Grow Plants in Lunar Soil – NASA.
- Paul, AL, Elardo, S. M. & Ferl, R. (2022). Plants grown in Apollo lunar regolith present stress-associated transcriptomes that inform prospects for lunar exploration. Nature.