But let’s back up: soil from Mars?
Of course, no one has yet brought back anything from the red planet, but spacecraft like NASA’s Phoenix Mars lander have analyzed Martian soil in great detail. Based on those measurements, scientists have come up with a reasonably good reproduction on Earth — crushed basalt from an ancient volcano in the Mojave Desert. It’s available for purchase, and Dr. Guinan bought 100 pounds.
Martian soil is very dense and dries out quickly — perhaps better for making bricks than growing plants, which have trouble pushing their roots through. That includes potatoes, the savior food for the fictional Mark Watney in “The Martian,” the book by Andy Weir and later a movie starring Matt Damon about a NASA astronaut stranded on Mars.
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.