Space has long been considered the final frontier. Yesterday, on 30th March 2020, Bob Behnken and Doug Hurley blasted off into space, marking this the first time in nine years that astronauts have been launched from American soil. As I’m writing, the two are in the middle of their 19 hour journey to the International Space Station (ISS). SpaceX and NASA are the partnership behind this mission, and hope that it will launch and new era of spaceflight. In fact, SpaceX is aiming beyond this, and was built on the goal of colonising Mars.
It could take up to ten months to travel there and once they arrive, one of the first, crucial steps will be establishing a farming structure with a good yield. Plants are an obvious choice, as they are easily stored, low maintenance and highly nutritious, but how does space affect the growth of plants, and can they be grown in Martian soil? In honour of this historic moment, we’re going to discuss the possibilities of growing and harvesting plants in space and on Mars.
Gravitropism in space
If you lay a seed on its side, you may notice that the emerging seedling sends its shoot up and its root down. Even in the pitch black, where light can’t guide growth. This is caused gravitropism (or geotropism). Plants are able to sense the pull of gravity and respond by growing in line with the gravitational pull. Shoots show negative gravitropism and so grow upwards against it, and root show positive gravitropism and grow down and with it. Even well established plants, such as the one in the left picture above, respond to gravitropism. If something occurs that causes the plant to fall over, it will continue to grow according to gravitational pull.
So what about in space or on Mars, where there’s little or no gravity? In the absence of gravity, roots growing in the dark grow in every direction. The seedling becomes highly reliant on light for guidance. A lack of gravity causes other problems for a plant, such as water tending to form bubbles. Containing soil, seeds, water and gases in an enclosed, functioning system is the only way to simulate normal growing conditions. The Vegetable Production System (or Veggie, for short) was developed to solve this issue and two Veggie units are aboard the ISS.
Each Veggie unit contains six “pillows” which contain a fertilised, growth medium that distributes water, nutrients and air around the roots. In 2015, the first lettuce was grown and eaten in space. Scott Kelly, Kjell Lindgren and Kimiya Yui enjoyed red romaine lettuce after a 33 day experiment to grow the plant in Veggie. They toasted their lettuce leaves before enjoying the fruits (or leaves) of their labour.
So far three types of lettuce, Chinese cabbage, mizuna mustard, red Russian kale and zinnia flowers have been successfully grown aboard the ISS. While this isn’t currently enough to sustain a crew for a 10 month journey to Mars, it’s enough to provide wellbeing to the crew aboard the ISS.
The current environment on Mars is undesirable at best. Its average surface temperature is -63°C, it receives half the sunlight of Earth, water is only available in a frozen state at the polar caps, and gravity on Mars is 62% lower than here on Earth. Given these things, it’s guaranteed that nothing can grow on the surface of Mars without considerable help (although, in 2016, Alien investigators claimed to see trees in pictures taken by NASA, but this was quickly debunked).
Terraforming, as its name suggests (“terra-” meaning “Earth”, and “-forming” meaning “shaping”), is the process of altering an environment to make it habitable to life from Earth. If you’d like a detailed video on how terraforming Mars could be achieved, I’ll leave this great video from Second Thought.
So what progress have we made towards growing plants in Martian soil or under Martian conditions? While all of the key macro and micronutrients required to grow plants have been detected in Martian soil, it hasn’t been in the correct quantities, or distributed across the entire surface, so fertilisers would have to be used. NASA is currently performing experiments with simulated Martian soil to see how plants could possibly be grown in it.
Accessing liquid water on Mars is another issue to be address. Calcium perchlorate exists in high quantities across the surface of Mars. This compound is toxic to plants and can decrease the amount of chlorophyll in plant leaves, which is important for photosynthesis, while also stunting plant growth and limiting root function. However, the compound could also prove crucial in accessing both water and oxygen. Calcium perchlorate absorbs water from the atmosphere and then releases it along with oxygen. If the compound can be effectively managed, it could become a key piece in the terraforming puzzle.
We’re a long way from colonising an uninhabitable planet, but yesterday’s expedition was a milestone on the journey towards regular spaceflight and, who knows, it might not be as long as you’d think before we see plants growing on the surface of Mars.