Denise Faustman, immunologist Harvard Medical School and Massachusetts General Hospital
I believe one of the greatest challenges of our era is to produce space stations and cities in outer space that can sustain quality life for long periods of time. The biological issues of weightlessness and how gravity maintains a role in cell division, resistance to infection and absorption of nutrients are poorly studied, and the obstacles in the field extend far beyond building rocket-powered craft to propel us to the heavens. The question of how life can co-mingle with gravity is a largely unexplored challenge that should be part of the important questions posed in our century. On a more humble level, the biology and control of cancer and the reason cancer exists in mammals might be lofty enough for experts. We still have not solved this perhaps more tangible problem as well!