Last month's announcement that NASA had discovered very strong evidence of flowing water on Mars renewed excitement over the possibility of humans living on Mars, as we prepare to send astronauts there within the next few decades. But if humans are going to survive on Mars, even temporarily, we need more than salty, cold water—we need food. 

That's why, for almost eight years, researchers based out of the University of Arizona have been working on a design for a martian greenhouse that would allow astronauts to grow food and, just as importantly, produce oxygen. 

"We operate it like a greenhouse, but it's not just a food production device. It's a fresh water generator, and the plants also keep us alive because plants make oxygen and we give the plants carbon dioxide," explained Gene Giacomelli, a horticultural engineer and co-principal investigator for the project, part of UA's Controlled Environment Agriculture Center. "It's a small, bio-regenerative life-support system and that's what NASA has, for many years, tasked us to develop."