Could we grow potatoes on Mars?
Exploring habitability, on our own world and beyond, is a research priority for the University of Warwick. Ares Osborn from Warwick’s astrophysics group, explores one aspect of this topic - growing food on Mars.
The 2015 blockbuster “The Martian” (based on a 2011 novel of the same name by Andy Weir) tells the story of astronaut Mark Watney’s struggle to survive on Mars and the rescue efforts to bring him home after he was left behind when his team’s mission was aborted. Part of this story is devoted to Watney’s efforts to keep himself alive by growing potatoes on Mars. But would this really be possible?
There are a lot of complications when sending food to Mars: payload space, shelf-life and degradation, refrigeration, nutritional quality and calorie content, and dietary preferences, amongst others. It is safe to say that if we are to settle as a colony on Mars semi-permanently or permanently, at some point in the distant future, we are going to have to learn how to farm on the planet and grow what we need to sustain ourselves during our stay.
Could the Mars soil support potato growing explored in The Martian?
In The Martian, Watney creates a large cylindrical space contained by clear plastic sheets, into which he dumps 126 square meters of Martian soil. To fertilise the potatoes, Watney turns to the only organic material present on Mars: human waste. This has been stored outside of the base, in foil packages, and he rehydrates all the waste with water to create a slurry.
Is this realistic? Experiments here on Earth have found successful germination of plants in both Moon and Mars soil simulants. Mars soil simulants have been found to hold water better than Earth soil and produce better growth of plant species. All essential minerals for plant growth have been found in amounts large enough to support plant life, apart from reactive nitrogen. This would usually be present on Earth in organic matter, but of course this is not present on Mars. So, this requires fertilisation, and the only organic matter available to Mark Watney is, of course, human waste.
But with human waste comes human pathogens – you wouldn’t want to eat vegetables grown that way here on Earth. Fortunately, in The Martian’s scenario the waste is desiccated and freeze-dried, and then exposed to the sub-zero temperatures of Mars, killing off any pathogens that may be present. So Watney could safely fertilise his potatoes with the nitrates and other elements present in the crew’s waste that are in low supply in the Martian soil.
Martian soil itself does, however, contain another hazard to human health – a group of chemical compounds called perchlorates. These were first found by the NASA Phoenix Lander in arctic Martian soil, and again found by Curiosity in Gale Crater. While the half a percent of perchlorate discovered does not seem like much, it would be toxic to humans. Perchlorates had not been discovered when The Martian was originally written, and were not included in the film, but the author, Andy Weir, has addressed this in an interview since then. “You can literally just rinse them out of the soil. Wash the soil, soak it in water, and the water would wash the perchlorates away,” he states. This would be important to do, as plants grown in untreated soil would accumulate perchlorates, and in eating the plants you would also ingest the toxins.
What other problems might Martian potatoes face?
Potatoes are sun-lovers, so for best growth they should be planted in an area with full-sun. This is a problem when on Mars. The red planet is further away from the Sun than the Earth, and the maximum brightness of the Sun on Mars is about 44% less than that on Earth – this is comparable to the sunlight in northern Canada in midwinter. Devon Island is a location on Earth that has similar solar insolation to Mars’ equator, making it a prime spot for plant research in Mars-analogous light. The Arthur Clarke Mars Greenhouse has been constructed here in order to research extreme-environment science and operations relevant to the challenges posed by Mars, and will, in the future, teach us about the limits of plant tolerance.
While Watney’s growing space in The Martian isn’t a greenhouse, there are lights set up around the perimeter of the crops. We can assume that these are grow lights, as Watney was conducting botany experiments on Mars even before he was stranded. So perhaps the sun-loving potatoes are getting enough light after all – but will they have enough gravity?
Mars has only one third of Earth’s gravity, so what happens to plants grown under gravity less than that of Earth? Plant roots know to grow ‘down’ due to a hormone called auxin. Tests on the International Space Station show auxin still has a vertical distribution in plants grown under microgravity, showing normal growth is still possible. Random positioning machines can be used to simulate partial gravity, testing germinating seeds at Moon and Mars gravity levels in comparison to an Earth gravity control. While the growth of plants under Moon gravity suffers, plants at Mars gravity can be similar to the Earth control, suggesting that Mars’ lower gravity is not an issue. Some studies have shown low gravity to cause stress to plant cells however, so the end result is not clear in the long run.
The end to Watney's journey and the start of ours?
In The Martian, potatoes are successfully harvested after 48 sols (a Martian solar day – 24 hours 39 minutes long), but the success of the venture does not last: Watney’s potato-growing is put to an abrupt end as the front of his habitat blows off, exposing his entire crop to the Martian air. The same intense cold that rendered his fertiliser safe now proves his downfall, the potatoes freeze over in an instant and the soil is sterilized.
The Martian is a work of science fiction. At present, a crewed mission to Mars remains a distant prospect rather than a reality. If we do get there, any attempt to grow crops on Mars will likely be a closely monitored and intensively resourced team effort, rather than a work of desperate improvisation. But like a lot of good science fiction, this story highlights some of the challenges humanity may one day encounter and the ways in which they might be overcome. It helps to inform our understanding of both the new threats and the new possibilities the future may present.
18 August 2020
The Astronomy and Astrophysics group at Warwick is interested in a huge range of scales across the Universe: planetary systems, how they form, live and die; stars, stellar binaries and and the exotic physical processes that they allow us to explore; as well as the transient events which mark the end of stellar lifetimes and the galaxies stars inhabit across the Universe. The group started in September 2003 and is both an observational and theoretical group. The group makes use of a wide range of ground-based telescopes, such as ESO's Very Large Telescope (VLT) in Chile and the Isaac Newton Group of telescopes (ING) in the Canary Islands, or the Atacama Large Millimetre Array (ALMA), as well as space telescopes such as NASA's Chandra and ESA's XMM-Newton X-ray observatories and the Hubble Space Telescope. The Warwick astro group partners in the four large spectroscopic surveys (DESI, SDSS-V, WEAVE, and 4MOST) that will start operations throughout 2020-2021.
IMAGE CREDIT: NASA, @MARSCURIOSITY.
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