An artist’s conception of a portable Martian greenhouse currently being developed at NASA.
An artist’s conception of a portable Martian greenhouse currently being developed at NASA. The space agency’s vegetable-growing experiments inspired an astrobiologist and his undergraduate students to grow their own “Martian” vegetables. Credit: NASA

What do kale, carrots, lettuce, sweet potatoes, onions, dandelions, and hops have in common? They could all potentially be grown in Martian soil by future colonists, according to a recent project by a class of astrobiology students and their professor. In a new addition to the class, the students tried growing a variety of vegetables in simulated Martian soil to discover which edible species may be prospects for future colonists.

“The project combined my research—astrobiology and Mars—and my hobby of growing things,” said Edward Guinan, a professor of astronomy and astrophysics at Villanova University in Villanova, Pa. Guinan developed the Red Thumbs Mars Garden Project for his annual undergraduate-level astrobiology class and supervised the experiments, which concluded last month. The students, Guinan said, were very enthusiastic about growing their own Martian vegetables.

Kale, sweet potatoes, certain lettuces, and hops grew very easily, tasting no different than their terrestrial counterparts.

The undergraduate researchers attempted to raise more than a dozen vegetables and herbs in a Mars-like soil with Mars-level light conditions. They found that kale, sweet potatoes, certain lettuces, and, surprisingly, hops grew very easily, tasting no different than their terrestrial counterparts. Other foods, including regular russet potatoes—the famous staple of the stranded astronaut in the 2015 film The Martian—required special soil or light treatments.

Guinan plans to repeat these experiments with future astrobiology classes and incorporate more rigorous scientific testing of the results. He presented the results this morning at the 231st meeting of the American Astronomical Society in National Harbor, Md.

Soil of a Different Color

The Red Thumbs Mars Garden Project was a new addition to his regular astrobiology course, Guinan explained. He was inspired by NASA’s Vegetable Production System (Veggie) on the International Space Station and wanted to bring those types of experiments to his students.

Guinan (right) and two of his students (left) are tending some of their plants grown in a brick-red Martian soil simulant seen in the frontmost plant (a pea plant). Some of their plants grew well in a Mars-like environment, whereas others required different light or temperature conditions that weren’t possible with the class’s single greenhouse setup. Credit: Villanova University

Guinan and his class grew the plants in a greenhouse in a commercially available Mars soil simulant similar to one developed by NASA and the Jet Propulsion Laboratory in Pasadena, Calif. The soil is mostly an iron-rich basalt with some additional reagents to better approximate the composition of Mars’s regolith as measured by NASA’s Curiosity rover and other instruments.

“The major differences are that Mars soil has about double the iron as Earth soil, mainly iron oxides, and Earth soil is more organic,” Guinan said.

The soil used in the trial is approximately 93% similar to Martian regolith, with the main differences being the absence of some poisonous perchlorates present on Mars and the class’s addition of inorganic fertilizers to aid plant development. Mars’s soil lacks the living organisms in Earth’s soil that help plant life flourish, Guinan said, so Mars farmers would need to augment the soil with biologically rich materials like compost waste.

The students grew the plants in pots under Mars-like light conditions—about 44% the light level on Earth. They then compared their plants to the same plant varieties grown in pots in regular potting soil.

Although the light intensity was Mars-like, the atmosphere was Earth-like: Plants on Mars would need to be grown in a greenhouse with an Earth-like atmosphere, Guinan said, because they would struggle to survive in Mars’s thin, cold, and dusty atmosphere. The need for indoor cultivation actually offers a benefit, he said, because the plants’ respiration could become part of the atmospheric recycling of a colony.

Martian greenhouses would need to maintain a constant 50%–60% humidity to avoid soil dryness.

Even with the right, nonpoisonous composition, the students ran into some issues with the soil. Mars’s regolith, a very fine, claylike powder, dried out very quickly if not constantly watered. Soil dryness was solved by regular watering, although Guinan estimated that Martian greenhouses would need to maintain a constant 50%–60% humidity to avoid soil dryness.

The soil also packs too tightly to let roots or subsurface vegetables grow, they found. The class solved the soil density problem by aerating it with some shredded cardboard or vermiculites to give the roots and veggies room to grow. Cardboard was more ideal, Guinan explained, because it might already be part of shipping material people would take to Mars and colonists wouldn’t need to import unneeded supplies.

A Variety of Martian Produce

With soil aeration and moisture levels accounted for, Guinan’s students found that each of the plants they tested grew moderately well. However, sweet potatoes, carrots, onions, kale, dandelions, basil, garlic, and hops were particularly robust crops under Martian conditions. The greenhouse was too hot for peas and spinach, Guinan explained, or they probably would have survived, too.

Some of the vegetables, herbs, and salad greens grown in a Martian soil simulant by Villanova undergraduate students. In this corner of the greenhouse, hops flourish in the frontmost tray, kale and lettuces fill the left tray, and dandelion bins occupy planters in the center rear of the image. Credit: Villanova University

“Of course, the students also picked potatoes because of The Martian,” Guinan said, “but the soil was too dense at first and the potatoes would not grow in it—they were squeezed. Once we added about one-third of some filler into the soil to give the potatoes room to breathe, they grew very well.”

Some business majors in the class opted to grow hops, a beer-brewing ingredient, and toyed with ways to market “Mars Beer,” Guinan explained. He noted, however, that some enterprising brewers beat them to the punch with their own hops and sorghum grown in simulated Martian soil prior to the Villanova tests.

Although none of the produce raised in Mars simulant soil tasted noticeably different from the experimental control crops, Guinan expressed concern that some of the typically iron rich leafy vegetables, like kale and spinach, might take up excessive iron from the Martian soil. Too much iron in food, he explained, can cause indigestion or even food poisoning. Guinan plans to have future classes test the iron content of the Mars-grown salad greens to see if the soil’s iron enrichment is reflected in the leaves. If so, that would be another potential concern for future Mars farmers.

“The farther and longer humans go away from Earth, the greater the need to be able to grow plants for food, atmosphere recycling, and psychological benefits,”

Although NASA may be growing veggies in space, Guinan said that his class’s experiments add variety. “Once we treated the Martian soil correctly, pretty much everything grew well,” he said.

“The farther and longer humans go away from Earth, the greater the need to be able to grow plants for food, atmosphere recycling, and psychological benefits,” said Gioia Massa, a payload scientist for Veggie at NASA’s Kennedy Space Center in Cape Canaveral, Fla. “I think that plant systems will become important components of any long-duration exploration scenario,” Massa added.

Future Harvests

This first set of Villanova vegetable tests was just the start, according to Guinan. In his opinion, the students chose their vegetables on the basis of what they liked to eat, rather than what would be the most nutritious or valuable for potential Mars colonists. When he repeats this project with future classes of astrobiology students, he said, he plans to have the students test vegetables, herbs, and possibly fruit that would be more likely to be selected by colonists.

Now that the Red Thumb Project is a proven success, Guinan has received a more dedicated greenhouse space to use for his class’s next vegetable patch. The new space, he explained, will give his class more control over the temperature, humidity, and light conditions for the plants and let them refine their experiments.

“This time, we’ll be growing from January through the summer, so we’ll have more time to evaluate what’s growing” and to also test slower-growing plants, Guinan said.

He also recommends this sort of project to other astrobiology teachers looking for a way to spruce up their courses. “It’s easy to set up, it worked well, and the students loved it.”

—Kimberly M. S. Cartier (@AstroKimCartier), News Writing and Production Intern


Cartier, K. M. S. (2018), Tests indicate which edible plants could thrive on Mars, Eos, 99, Published on 12 January 2018.

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