The search for habitable worlds: Planetary exploration in the 21st century

The search for and detailed characterization of habitable environments on other worlds-places where liquid water, heat/energy sources, and biologically important organic molecules exist or could have once existed-is a major twenty-first-century goal for space exploration by NASA and other space agencies, motivated by intense public interest and highly ranked science objectives identified in recent National Academy decadal surveys. Through telescopic observations, terrestrial laboratory and field studies, and a "flyby, orbit, land, rove, and return" strategy for robotic exploration, particular emphasis will be placed on specific worlds already identified as potentially habitable: Mars, Jupiter's ocean moon Europa, and Saturn's icy and organic-bearing moons Titan and Enceladus. However, the potential abounds for surprising discoveries at many of our solar system's other planetary, satellite, and asteroidal destinations, as well as within newly discovered planetary systems around other stars.