In the movie The Martian, astronaut Mark Watney (played by Matt Damon) survives by being stranded on the Red Planet growing potatoes in Martian soil fertilized with feces.
Future Mars astronauts could cultivate land-based crops to avoid relying solely on refueling missions and cultivating a greater amount and variety of food than with hydroponics alone (SN: 11/4/11). But new laboratory experiments suggest that growing food on the Red Planet will be much more complicated than simply planting crops with poop (SN: 22/09/15).
The researchers planted lettuce and the Arabidopsis thaliana weed in three types of fake Mars dirt. Two were made with materials extracted in Hawaii or the Mojave Desert that look like dirt on Mars. To mimic the composition of the Martian surface even more closely, the third was made from scratch using volcanic rocks, clays, salts, and other chemical ingredients that NASA’s Curiosity rover saw on the Red Planet (SN: 1/31/19). While both lettuce and A. thaliana have survived on Mars-like natural soils, neither could grow in synthetic dirt, researchers reported on Jan. 15 next to Icarus.
“It’s no wonder at all that as you go (dirt) it’s getting more accurate, closer to Mars, making it harder and harder for plants to grow in it,” says planetary scientist Kevin Cannon of the Colorado School of Mines in Golden, Colo., Which helped make the synthetic earth of Mars but did not participate in the new study.
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The soil on Earth is full of microbes and other organic matter that helps plants grow, but the dirt on Mars is basically crushed rock. The new result “tells you that if you want to grow plants on Mars using the soil, you’re going to have to work hard to turn that material into something that plants can grow,” Cannon says.
Biochemist Andrew Palmer and colleagues at the Florida Institute of Technology in Melbourne planted lettuce and A. thaliana seeds in imitation of Mars land under controlled lighting and temperature indoors, as did astronauts on Mars. The plants were grown at 22 ° C and about 70 percent humidity.
The seeds of both species germinated and grew in soil extracted from Hawaii or the Mojave Desert, as long as the plants are fertilized with a cocktail of nitrogen, potassium, calcium, and other nutrients. No seed of either species could germinate in synthetic dirt, so “we would grow plants in hydroponic conditions and then transfer” to artificial dirt, Palmer says. But even when they received fertilizer, those seedlings died within a week after transplanting.
Palmer's team suspected that the problem with Mars' synthetic dirt was its high pH, which was about 9.5. The two natural soils had pH levels around 7. When the researchers treated the synthetic dirt with sulfuric acid to lower the pH to 7.2, the transplanted seedlings survived one more week but eventually died.
The team also found another problem: the original recipe for synthetic dirt did not include calcium perchlorate, a toxic salt that recent observations suggest accounts for about 2 percent of the Martian surface. When Palmer's team added it to concentrations similar to those seen on Mars, neither lettuce nor A. thaliana grew at all on Earth.
“Perchlorate is a major problem” for Martian agriculture, says Edward Guinan, an astrobiologist at Villanova University in Pennsylvania who did not participate in the work. But calcium perchlorate may not have to be an obstacle. “There are bacteria on Earth that enjoy perchlorates as food,” Guinan says. As microbes eat salt, they give off oxygen. If these bacteria were taken from Earth to Mars for perchlorate lunches on Martian earth, Guinan imagines that organisms could not only get rid of a toxic component of the earth, but perhaps also help produce respirable oxygen for astronauts.
What’s more, the exact treatment needed to make Martian dirt cultivable can vary, depending on where the astronauts make their property. “It probably depends on where you land, what the geology and chemistry of the soil will be,” Guinan says.
To explore how that variety may affect future farming practices, geochemist Laura Fackrell of the University of Georgia in Athens and her colleagues mixed five new types of fake dirt from Mars. The recipes for these fake Martian materials, also reported in the January 15 Icarus, are based on observations of the Mars surface from the rovers Curiosity, Spirit and Opportunity, as well as NASA's Mars Global Surveyor and Mars Reconnaissance Orbiter spacecraft.
Each new artificial dirt on Mars represents a mixture of materials that could be found or manufactured on the Red Planet. One is designed to represent the average composition on Mars, similar to the synthetic material created by Cannon’s team. The other four varieties have slightly different makeups, such as dirt especially rich in carbonates or sulfates. Fackrell says this collection “expands the palette of what we have available” as test benches for agricultural experiments.
He is now using his stock to conduct preliminary plant growth experiments. So far, a legume called moth bean, which has a nutritional content similar to soybeans but is more drought-resistant, has grown better. “But they’re not necessarily super healthy,” Fackrell says. Future experiments could explore how nutritious cocktails help plants survive in the various false Martian terrains. But that's clear, says Fackrell, "It's not as easy as it sounds in The Martian."