Kevin Hand, NASA Jet Propulsion Laboratory
In the next few decades, increasingly capable robotic spacecraft will reveal if other worlds in our solar system harbor life. Similarly, new space telescopes will yield information about the chemical composition of planets orbiting distant stars. Understanding what makes a planet habitable, and what chemical and geological signatures are produced by its inhabitants, is critical if we are to move the science of biology beyond Earth. In this session we address our understanding of habitability as constrained by our knowledge of life on Earth, and as challenged by our rapidly expanding knowledge of environments found on other worlds. The broad requirements for life on Earth include liquid water, a suite of biogenic elements (C, H, N, O, P, S), and a source of energy. The production and stability of surface and subsurface liquid water environments is examined in the context of Mars, Europa, Titan, and Enceladus. The availability of chemical and radiation energy on these worlds is also considered, with particular attention given to the minimal energy requirements measured for life on Earth. Finally, we address the task of detecting life on these other worlds both from orbit and with surface landers.