Any long-term human presence on Mars is going to require renewable food sources, and that likely involves plants. But how do we know that they'll flourish in the Red Planet's higher radiation and lower gravity? NASA may find out in the next several years. One of the proposed modules on its next Martian rover is the Mars Plant Experiment (MPX), a tiny greenhouse that would study plant growth. The experiment would use Earth air and water to keep a batch of flowering plants alive for 15 days and see how they're affected by otherworldly conditions.