For the most part, the students chose practical, nutritious plants like soy beans and kale in addition to potatoes. Some added herbs like basil and mint so that astronauts could enjoy more flavorful food on thesolar system’s fourth world.
And one group chose hops.
“Because they’re students,” Dr. Guinan said. “Martian beer.” (He vetoed marijuana.)
For the experiments, the students had a small patch of a greenhouse, with a mesh screen reducing the sunlight to mimic Mars’ greater distance from the sun.
What did “fabulous” in pure Martian soil was mesclun, a mix of small salad greens, even without fertilizer, Dr. Guinan said.
When vermiculite, a mineral often mixed in with heavy and sticky Earth soils, was added to the Martian stuff, almost all of the plants thrived. Because astronauts would likely not be hauling vermiculite from Earth but might have cardboard boxes, Dr. Guinan also tried mixing cutup cardboard into the Martian soil. That worked too.
One group of students hypothesized that coffee grinds could similarly be used as a filler to loosen up the soil. They figured the astronauts would be drinking coffee anyway, and coffee would also be a natural fertilizer. “Also, it may help acidify Martian soil,” said Elizabeth Johnson, a Villanova senior who took the class. Mars soil is alkaline, with a pH of 8 to 9, she said, compared to 6 to 7 on Earth.
“We think the coffee has a lot of potential,” Ms. Johnson said.
Her team’s carrots, spinach and scallions sprouted quickly in the mix of coffee grounds and Martian soil, initially growing faster than even plants in a control planter full of Earth potting mix.
Dr. Guinan is not the first to try growing plants in Martian soil. Five years ago, Wieger Wamelink, a scientist at Wageningen University and Research in the Netherlands had the same idea, a way to combine his work — ecology research — with his interest in science fiction.
The first round of experiments grew 14 types of plants including rye, tomatoes and carrots in Martian soil, simulated lunar soil and Earth soil. Almost all of the plants germinated, Dr. Wamelink and his colleagues reported.
Like Dr. Guinan, Dr. Wamelink found that mixing organic material into Martian soil greatly improved plant growth. They verified that crops grown in Martian soil were equally nutritious and safe to eat. In 2016, the researchers hosted meals cooked from their research crops for more than 50 people who had supported the work with crowdfunding donations.
Last year, they showed earthworms could live, even reproduce, in Martian soil.
Future experiments might grow bamboo, which could also be useful on Mars. “Not because we want panda bears over there,” Dr. Wamelink said. The shoots are edible, and “It’s also a good building material,” he said.
One aspect that Dr. Guinan and Dr. Wamelink have not tackled yet is the presence on Mars of perchlorates, a poisonous chemical that causes thyroid problems in people. (For safety, the simulated Mars soil leaves that out.)
It might be possible to rinse out the perchlorates, which are soluble in water. Bacteria that eat perchlorates might also be used to cleanse the soil.
This semester, two Villanova astronomy students will perform follow-up experiments. That includes attempting to grow barley, the other essential ingredient for future Martian beer.