Growing plants on the moon is no longer an option

• Researchers have cultivated a fast-growing plant in lunar soil samples brought back by astronauts in the 1970s, according to our partner The Conversation.

• The experiment demonstrated that plants could be grown in lunar habitats but the location of the habitat should be guided by the maturity of the soil.

• This analysis was conducted by Monica Grady, professor of planetary and space sciences.

What do you need to grow your garden?

Good sunshine and light showers, bees and butterflies to pollinate, but also good soil, rich in essential minerals.

Imagine having no rich soil, no showers, no bees, no butterflies, and the sun is either too strong and too direct, or completely absent, leading to freezing temperatures.

Could plants grow in such an environment?

If so why ?

This is a question that colonists of the Moon (and Mars) will have to answer if (or when) human exploration of nearby planets continues.

A recently published study is beginning to provide answers.

The researchers behind this study grew the fast-growing plant

in samples of lunar 'regolith' (that's the name of the Moon's soil), brought back from three different locations on the Moon by astronauts. Apollo missions in the 1970s.

​A dry and barren lunar soil

This isn't the first time we've tried to grow plants in lunar regolith, but it's the first time we've demonstrated why they don't thrive.

Indeed, lunar regolith is very different from terrestrial soils: it does not contain the organic matter characteristic of terrestrial soil (worms, bacteria, decomposing plant matter), and it is very dry.

However, it is composed of the same minerals as the earth's soils.

So, assuming that the lack of water, light and air is compensated by growing the plants inside a lunar habitat (a greenhouse for example), the regolith could have the potential to grow plants.

This study shows that this is indeed the case.

The seeds of

germinated at the same rate in the regolith brought back by Apollo as in the earth's soil.

But while the plants in the earth's soil developed roots and leaves, the seedlings of the Apollo samples were stunted and their roots did not grow well.

The primary goal of the study was to examine plants at the genetic level and specifically identify the environmental (stress) factors that elicit the most important genetic responses.

Scientists found that most of the stress responses in Apollo plants came from salts, metals, and highly reactive oxygen in lunar samples – the latter two not being common in Earth's soil.

Plants grown in the Apollo samples were affected to varying degrees: those in the Apollo 11 samples were the slowest to develop.

The chemical and mineralogical compositions of the three lunar soils were quite similar to each other and also to the composition of the terrestrial sample.

The researchers therefore suspected that the nutrients were not the only force at play.

In fact, the "Earth's soil", called JSC-1A, was not an ordinary soil, but a mixture of minerals prepared specifically to simulate the lunar surface.

It therefore contained no organic matter.

The starting material for JSC-1A was basalt (just like in the lunar regolith), to which the scientists added natural volcanic glass, to play a role analogous to that of "glassy aggregates", these small mineral fragments mixed with molten glass that are abundant in lunar regolith.

Scientists believe that these aggregates are a potential reason for the lack of seedling growth in lunar soil compared to Earth soil, and also explain the different growth patterns between the three lunar samples.

Aggregates are common on the surface of the Moon.

Ironically, they are formed by a process called 'moon gardening', or 'spatial weathering': the way the regolith changes due to the bombardment of the Moon's surface by cosmic rays, solar wind and tiny meteorites.

Since there is no atmosphere to slow down the tiny meteorites that hit the surface, they smash together at high speed, causing melting and then quenching (i.e. rapid cooling) at the site of impact.

Gradually, small aggregates of minerals form, held together by glass.

They also contain tiny particles of metallic iron (“nano-phase” iron) formed by the spatial weathering process.

It is this iron that makes the biggest difference between the glassy aggregates of the Apollo samples and the natural volcanic glass of the Earth sample.

It is also the most likely cause of metal-associated stress, which has been identified in shoot genetic profiles.

Thus, the presence of aggregates in lunar substrates caused the difficulty of Apollo seedlings compared to seedlings grown in JSC-1A, especially those of Apollo 11. Indeed, the abundance of aggregates in a lunar regolith sample depends on the duration of exposure of the material on the surface of the lunar soil, what is called its "maturity".

The most mature soils have been exposed on the surface for a long time, in places where the regolith has not been disturbed by recent impacts;

while immature soils are found around recent impact craters and on the steeper slopes of craters, where materials originally lying below the surface become exposed.

The three samples from the Apollo missions had different maturities, with the material from Apollo 11 being the most mature.

It contained the most nanophase iron, and

shoots grown in these samples had the highest metal-associated stress markers in their genetic profile.

The importance of young soil

The study concludes that the more mature regolith was a less effective substrate for the growth of seedlings than the less mature soil.

This finding is important because it demonstrates that plants could be grown in lunar habitats using regolith as a resource, but the location of the habitat should be guided by soil maturity.

And a final thought: it seemed to me that these conclusions could also apply to certain poor regions of our world.

I don't want to repeat the old argument "Why spend all this money on space research when it could be better spent on schools and hospitals?"

– that would be the subject of a whole other article.

Our "MOON" file

But are there technological developments resulting from this research that could be applicable on Earth?

Could what we have learned about stress-related genetic modifications be used to develop crops that are more resistant to drought?

Or plants that could tolerate higher levels of metals?

If growing plants on the Moon could help gardens become greener on Earth, that would be a great achievement.

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This analysis was written by Monica Grady, Professor of Planetary and Space Science at the Open University (UK).

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Declaration of interests

• Planet

• Podcast

• The Conversation

• Moon

• Space

• Nasa

• Agriculture

• plants