May 13 2022

Scientists Grow Plants in Lunar Soil

After years of requesting tiny samples of lunar soil, plant scientists at the University of Florida were finally granted 12 grams to work with (out of the 382 kg brought back during the Apollo missions). They had proposed a simple experiment – could seeds germinate and plants grow in lunar soil? It turns out the answer is yes, sort of.

The researchers used Arabidopsis, or rockcress, which is a genus that contains the first plant to have its entire genome sequenced and is therefore a favorite of plant biologists.  They added nutrient rich water to one gram pots of lunar soil and planted Arabidopsis seeds in them. As controls they planted the same seeds with the same nutrients in regular soil, and simulated lunar and Martian soil, plus Earth soil but from extreme environments. All of the seeds sprouted. For about the first six days the plants all seemed to be doing equally well, but then it became clear that the plants growing in lunar soil were smaller, more varied in size, and were showing signs of stress.

The experiment was therefore a partial success – the plants grew surprisingly well but did not thrive in the lunar soil. Because they used Arabidopsis, they were able to also track gene expression in the plants. The plants growing in lunar soil had increased expression of genes related to stress, reinforcing the conclusion that there is something about the lunar soil that is not friendly to the plants, causing them to react as if they were growing in an extreme environment.

Interestingly, the researchers had two different type of lunar soil from different locations. One type is referred to as “mature” lunar soil, which was exposed directly to the solar wind. They also had not mature lunar soil, in which the plants fared a little better.

This is just step one in the process, and raises many questions the researchers hope to answer with further studies. What is it, exactly, about the lunar soil that is stressing out the plants? There are many differences in mineral composition and structure of lunar soil, and plants are simply evolutionarily adapted to Earth soil. Are there any analogies with extreme environments on Earth. How can the increased stress be mitigated? Perhaps tweaking the nutritional additives are necessary, or perhaps the lunar soil needs to be processed in some way, or some component needs to be removed. On the plant side researchers can also search for ways to enhance the plant’s ability to adapt to the lunar soil. They could find plant varieties that fare better. Given enough time and resources they could cultivate plants that are better adapted to lunar soil, or even genetically engineer them.

The obvious application of this research is to be able to farm plants on the moon, and eventually Mars (once we get our hands on some Martian soil). Plants are extremely useful to settling space and other worlds. They produce food and oxygen while removing carbon dioxide from the air. They can be engineered to produce useful chemical and drugs. Being able to locally source things like food and drugs is critical to having a sustainable settlement away from Earth. Plants are also psychological beneficial to the people who would be living there.

The moon is also of particular interest because it will likely serve as the gateway to the rest of the solar system and beyond. Getting out of Earth’s gravity well is challenging and uses a lot of energy. About 90% of the chemical rocket fuel necessary to go anywhere in the solar system is used just getting into Earth orbit. This depends a little on how fast you want to get to your destination, but assuming a similar final velocity, the 90% figure holds, at least as a good approximation. Having a spacefaring infrastructure therefore depends on getting away from the tyranny of Earth’s gravity and the rocket equation. This makes the moon, with its much weaker gravity while still being relatively close to the Earth, an ideal platform.

We may, therefore, design our space infrastructure so that as much of the stuff necessary to travel and live in space is sourced from the moon. This avoids having to lift a lot of stuff, other than people, off the Earth itself. If we can produce water, oxygen, fuel, and food on the moon, then it becomes a stepping stone to any other destination. Plants will likely play a critical role in any such scheme, as they can produce food, fuel, and oxygen. Water will perhaps be the most critical resource in space, which is why NASA has invested so much effort to identify where and how much water is trapped in the lunar soil, and why we may build our first lunar stations at the poles where permanent shadows have preserved possibly large water supplies.

A less obvious use of this lunar plant research is developing plants that are better adapted to extreme conditions on Earth. This may become increasingly important as climate change creates hotter and dryer environments.

The Artemis mission plans to return people to the moon in 2025.  This will allow us to replenish our supply of lunar regolith, giving a huge boost to such research. Likely one of the main goals of any future lunar base will be to further this research on the moon itself, which has different gravity and light conditions (if natural light is used) than on Earth. It’s probably not going to be easy, but the results of this current experiment are encouraging. At least we know plants can grow in lunar soil – they don’t immediately die or fail to germinate because of some toxic component. This opens the door to farming the moon, increasing its prospects as a gateway to the solar system.

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