In Andy Weir's novel-turned-Matt-Damon-movie The Martian, the protagonist endures the harsh terrain of Mars by using his own shit to grow potatoes. The idea isn't that outlandish -- over the last few years, a NASA-backed project has been attempting to simulate Martian potato farming by growing taters in the Peruvian desert. While early results were promising, new research suggests that survival of any life on Mars -- much less potato-growing humans -- might be more difficult than we thought. I blame Matt Damon.