As many of us witnessed in director Ridley Scott's sci-fi drama "The Martian," the soil of Mars is devoid of the organic nutrients otherwise vital to support plant life. To get around this, the character of Mark Watney, played by Matt Damon, uses his own feces to supplement the otherwise dead soil and grow potatoes. But does this science match up with how the first Mars farmers might actually introduce agriculture to the red planet?
In addition to experimenting with crops grown in space, NASA is beginning to trial "Martian Gardens" to figure out the kinds of vegetables that might tolerate soil sourced from the red planet.
"Soil, by definition, contains organics; it has held plant life, insects, worms. Mars doesn't really have soil," Ralph Fritsche, the senior project manager for food production at Kennedy Space Center, said in a news release.
In an effort to simulate the crushed volcanic rock on Mars, researchers gathered 100 pounds of similar soil from Hawaii. Starting with lettuce, they monitored growth under three variables: one in simulant, one in simulant with added nutrients and one in potting soil. Surprisingly, about half the lettuce grown under Mars' soil conditions managed to survive — but with weaker roots and a longer growth period. The vegetable, for those curious, tasted exactly the same, the researchers reported.
The team plans to experiment with a variety of nutritious vegetables such as radishes, Swiss chard, kale, Chinese cabbage, snow peas, dwarf peppers and tomatoes.
In a separate experiment, scientists at Kennedy Advanced Life Support Research are working on the Prototype Lunar/Mars Greenhouse Project, which aims to figure out how to grow vegetables for astronauts on Mars, the moon or anywhere else in outer space where produce cannot be supplied from Earth.
"We're working with a team of scientists, engineers and small businesses at the University of Arizona to develop a closed-loop system. The approach uses plants to scrub carbon dioxide, while providing food and oxygen," Dr. Ray Wheeler, lead scientist in Kennedy Advanced Life Support Research, told Phys.org.
The prototype itself is an inflatable, deployable system that researchers call a bioregenerative life support system. As crops are grown, the system recycles, water, recycles waste, and revitalizes the air. The system is hydroponic, so no soil is needed. Water that is either brought along on missions or gathered in situ — on the moon or at Mars for example — is enriched with nutrient salts, and flows continuously through plant root systems. Air in the system is recycled too. Astronauts exhale carbon dioxide, which plants absorb. Through photosynthesis, the plants produce oxygen for the astronauts.
Back to 'The Martian' for a sec
Could Matt Damon's character really have given life to Mars' soil using only his feces? Yes and no. One thing neither the movie nor the book it's based on ever mentions is that Mars' soil contains perchlorates, a kind of salt that's hazardous to humans.
"Anybody who is saying they want to go live on the surface of Mars better think about the interaction of perchlorate with the human body," Peter Smith, principal investigator for NASA's Phoenix mission to Mars, said in 2013 to Space.com. "At one-half percent, that's a huge amount. Very small amounts are considered toxic. So you'd better have a plan to deal with the poisons on the surface."
As "The Martian" author Andy Weir later discovered, it's apparently a fairly easy problem to overcome.
"You can literally just rinse them out of the soil," he told Modern Farmer. "Wash the soil, soak it in water and the water would wash the perchlorates away."
The other problem with using feces to supplement organic nutrients is that it also contains human pathogens. While our own pathogens won't harm us, a mix of feces from other crew members might quickly lead to a problem. Thankfully, Weir had a solution for that one in his book.
"The crew's waste was all completely desiccated, freeze-dried, and then dumped out on the surface of Mars and bagged," Weir added to MF. "Any pathogens in there would have been dead."
Let's just hope NASA figures out a more palatable method to grow the first vegetables on Mars.
Editor's note: This story has been updated with new information since it was originally published in October 2016.