The first humans to live on Mars might not identify as astronauts, but farmers. To establish a sustainable settlement on Earth's solar system neighbor, space travelers will have to learn how to grow food on Mars -- a job that could turn out to be one of the most vital, challenging and labor-intensive tasks at hand, experts say. "One of the things that every gardener on the planet will know is producing food is hard -- it is a non-trivial thing," Penelope Boston, director of the Cave and Karst Studies program at New Mexico Institute of Mining and Technology, said...