Plants will grow in lunar regolith, but they don’t like it

Enlarge / Plants grown in lunar soil (right) aren’t as happy as those grown in soil meant to simulate it (left).

Tyler Jones, UF/IFAS

Like anyone who has read or watched The extent or The Martian knows, growing plants in space has big advantages. Plants can help maintain a healthy atmosphere because they recycle water and add variety to diets. Although they can be grown hydroponically, the process requires a significant amount of water, which may not be enough. So for missions that will land on a body like the Moon or Mars, growing plants in the local soil might be a better fit.

But the local soils of these bodies are unlike those we find on Earth, which contain a complicated mix of minerals, organic compounds and microbial life. Can plants adapt to these differences? A group of researchers from the University of Florida – Anna-Lisa Paul, Stephen Elardo and Robert Ferl – set out to find out, and they used an incredibly rare material: lunar soil returned from the Apollo missions.

In the mix

Lunar soil exists in a form called regolith, which is essentially loose, dusty material created by the constant bombardment of lunar rocks by micrometeorites. When the first samples were returned to the time of Apollo, studies of this regolith’s interactions with living things focused on the fear of pathogens that could pose a danger to life on Earth. As a result, plants and seeds were briefly exposed to lunar soil and then tested to see if this exposure impaired their growth. There was no attempt to grow anything in the ground.

NASA has since developed a material made on Earth, called JSC-1A, intended to simulate lunar soil. But there are significant differences between it and the lunar soil. These include chemical differences, with the lunar regolith containing higher amounts of titanium and some trace elements than JSC-1A. Earth’s oxidizing environment also creates differences in the chemical state of some of the metals present, including that of iron, a key component of many enzymes, such as those involved in photosynthesis.

Finally, there are physical differences between the material and the soil. The rapid melting and cooling caused by micrometeorite impacts on the regolith creates small balls of glassy material. JSC-1A uses volcanic glasses to approximate this process, but there are still physical differences.

So the researchers decided to try to work with the real thing, using JSC-1A as a control. And with the help of Johnson Space Center staff, they obtained three different lunar samples returned from Apollo 11, Apollo 12, and Apollo 17. The samples all came from regions of volcanic origin but differed in age, material from Apollo 11 having the longest surface exposure and Apollo 17 the shortest.

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