The following is an extract from our monthly Launchpad newsletter, in which resident space expert Leah Crane journeys through the solar system and beyond. You can sign up for Launchpad for free here.
Perhaps the least pleasant thing about places other than Earth is that they don’t have trees (as far as we know). But scientists around the world are working on ways to grow plants in space and on other worlds, so someday that might change.
There are many reasons aside from aesthetics to try growing things in space. The obvious one is to provide food to explorers, especially those on future long-duration trips beyond Earth, spent either in spacecraft or on other worlds such as the moon or Mars.
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Another benefit for astronauts is psychological – numerous studies have shown that gardening, and even generally having plants around, can make people feel happier and calmer. As astronaut Christina Koch recently told me: “There were definitely days where I would go over to our tiny greenhouse, which is about the size of a couple of shoe boxes, and just smell the plants. Just to smell something that was organic, that actually did a lot for me.” You can imagine how looking into the vastness of space or the bleak landscape of Mars might be dispiriting, and seeing the greenery that we might take for granted on Earth could be comforting.
Plants also produce oxygen, and they can help make soil more fertile as generations of them grow and die. This could create a sort of feedback process that would make growing plants easier and easier over time.
But it’s going to start out difficult. For one thing, anywhere in space that we could send human explorers in the near future – meaning a space station, the moon or Mars – is cold and full of dangerous radiation. You can’t just go outside and plant a garden. “There are a few reasons you couldn’t just chuck plants on the moon – they wouldn’t survive the lunar temperature or the radiation,” says Jessica Atkin at Texas A&M University. “You’d have to grow them inside the habitat with the same protections as the astronauts.” That goes not just for the moon but for pretty much any other location in space, too.
On a spacecraft, that should be no problem – the whole thing is already shielded to protect astronauts. The main issue is the lack of gravity. Roots display a property called geotropism or gravitropism, meaning they grow in the direction of gravity’s pull. When they’re in microgravity, such as on the ISS, they grow in every direction and tend to strangle one another. Microgravity also makes it difficult to water plants, as the water does not trickle into the soil in the same way. Researchers on the ISS and around the world are working on potential solutions to those two problems, including developing special lighting rigs to direct growth and wrapping sponges around the plants’ roots.
On another world, there will still be gravity, so gravitropism shouldn’t be too big a problem. The issue there is soil. Moon dust and Mars dirt are both full of toxic compounds and lacking in essential nutrients. That’s where Atkin’s work comes in. She and her team have successfully grown chickpeas in lunar soil by adding a combination of worms to provide nutrients and fungus to remove toxins. The plants survived and flowered, a promising result.
But building an off-world greenhouse is more challenging. It would probably mean constructing an entire ecosystem almost from scratch, with all sorts of other organisms and special equipment to make anything grow. “You need all of these other things for plants to thrive,” says Atkin. “I think a lot of the time people don’t see what’s going on underneath the ground and what a productive little world is down there contributing to our plants.”
Astronauts will probably bring most of their food with them for the foreseeable future, and maybe they’ll be able to supplement their diets with a few small vegetables or fruits. “It’s not going to be a salad bar anytime soon,” says Atkin. But maybe someday!
