The potential for life on other planets has vexed scientists for ions. For astrobiologist Kevin Hand, it's an obsession that began when he was a sci-fi-crazed kid and is likely to consume him well into middle age.

To think of a life with such a singular purpose is both "exhilarating and depressing,'' says Hand, 41, a National Geographic emerging explorer.

"The pendulum swings both ways,'' he says. "The overwhelming amount of personal time is superseded by the long view of humanity, exploration, and discovery. What fascinates me is that we will do the exploration that revolutionizes our understanding of whether or not life on Earth is a biological singularity or if in fact we live in a biological universe. Ultimately, the