Apollo 15: Irwin Scoops up Soil

Astronaut James B. Irwin scoops up lunar soil during Apollo 15, 2nd August 1971.
Image: NASA

When Neil Armstrong made his giant leap for humankind in 45 years ago, he got covered in Moon dust. Throughout the Apollo missions, dust was an issue. Fine but rough, it caused problems with the space suits, and created mini dust storms in the cabin once the landers launched back into space.

On Earth, mineral soils are formed from the underlying rock by weathering, which is a collection of natural processes that gradually break down the rock. Weathering can be mechanical (through atmospheric conditions such as heat, water, ice and pressure) or chemical (when the surface rock reacts with water, oxygen or chemicals produced by plants). The rock particles then combine with organic matter to form what we know as soil.

On the Moon, that doesn’t happen. Lunar dust is formed from lunar rock (regolith) when small meteorites hit the Moon’s surface and pulverize the rock. Some of the rock melts and then cools, coating the dust with a glassy shell. There’s no organic matter for the dust to combine with. UV rays by day, and solar winds by night, create charged particles and give lunar dust ‘static cling’. Oh, and tiny specks of iron make it magnetic. So it’s not your run-of-the-mill Earth soil.

But would anything grow in it? The short answer is no – the minerals it contains are locked up in a form that plants can’t access. Whilst it might be possible to use Moon rock as a ‘substrate’ for hydroponic growing (essentially there merely to hold the plants up), all of their nutrients would have to be supplied with a fertilizer.

But that’s not the final word on the subject. NASA did some plant experiments with Moon rock at the time of the Apollo missions (mainly as part of their quarantine procedures to make sure they hadn’t imported health risks with their souvenirs). They didn’t attempt to grow plants in lunar soil, but they exposed plants to it. Not only did they find no negative effects, the experiments seemed to show that the plants benefited from the Moon dirt – results that have not been replicated. Since then the Moon samples have been considered a precious commodity and have not been made available for destructive research such as grinding them up to grow plants. So researchers have to use ‘simulants’ – Earth rocks that are similar in type to those found on the Moon.

Early in the new millennium, a team of researchers led by Natasha Kozyrovska and Iryna Zaetz from the National Academy of Sciences in Kiev, conducted a series of experiments with French marigolds (Tagetes patula) in one such simulant – anorthosite. They published their results in 2006.

Unsurprisingly, seeds sown in plain old crushed anorthosite didn’t grow into plants. But they were the control group. A second set of seeds was inoculated with a microbiome (bacteria and fungi known to promote healthy growth), whilst the crushed rock was also seeded with bacteria – and in this more complex ecosystem the seeds were able to germinate and grow into flowering plants. The microorganisms present were helping the plants to extract nutrients from the rock, and the authors suggested that this might be a way of starting to grow plants on the Moon.

Reading through the paper, I got the impression that what the authors were proposing was a kind of space permaculture. Lunar regolith is sterile, which not only means that plants can’t rely on microorganisms to release nutrients, but also means that any soil made from them would be a blank canvas for microbes accidentally brought from Earth. Rather than fungi and bacteria that promote healthy growth, you could end up with an imbalance – an environment that is harmful to plant growth. The idea of inoculating the seeds and the regolith was to promote a healthy soil environment that could protect plants against pests and diseases.

French marigold

The selection of French marigolds was not random. The scientists wanted to grow ‘pioneer’ plants that would not to be too fussy to grow in the nutrient-deprived lunar soil. These ‘first generation’ plants would then be composted to create organic matter and real soil, but the goal was also for them to be multipurpose. They were looking for plants to recycle waste products and produce oxygen, which had potential nutritional and medicinal benefits, and that flowered and so could improve the psychological well-being of the astronauts. Providing all these benefits, whilst kick-starting a sustainable ecosystem that makes use of local resources, is a tall order – but apparently French marigolds fit the bill!

The paper mentions another problem with growing plants on the Moon – the Sun is up for about two weeks, and then down again for the same period of time. If you don’t want to go to the expense of supplementary lighting, it reasons, the only solution is to chill your plants so that they are dormant until the Sun comes out again. In the meantime, I guess those long nights are perfect for forcing vegetables and sprouting seeds! Or perhaps mushroom cultivation….


And so it’s time, once again, for you to choose the next leg of our space blog adventure! Would you like to know more about growing fungi in space, how scientists choose which crop plants will be grown in space, or the Moon trees (grown from seeds taken into orbit around the Moon during Apollo 14)? Cast your vote below, or if you have a suggestion for a different topic, leave a note in the comments 🙂

Update:
And you’ve chosen…

how to choose space veggies

References

NASA’s Dirty Secret: Moon dust

Kozyrovska, N. O., Lutvynenko, T. L., Korniichuk, O. S., Kovalchuk, M. V., Voznyuk, T. M., Kononuchenko, O., … & Kordyum, V. A. (2006). Growing pioneer plants for a lunar base. Advances in Space Research, 37(1), 93-99.

Gardening on the Moon