An open access publication of the American Academy of Arts & Sciences
Summer 2012

The Search for Habitable Worlds: Planetary Exploration in the 21st Century

James F. Bell III

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.

James F. Bell III is a Professor in the School of Earth and Space Exploration at Arizona State University in Tempe and President of The Planetary Society. He has been involved in many of NASA's recent robotic solar system exploration missions, including as lead scientist for the Pancam color stereo cameras on the Mars rovers Spirit and Opportunity and as a member of the science camera team on the Curiosity rover. He has published the space photography books Postcards from Mars, Mars 3-D, and Moon 3-D. He received the 2011 Carl Sagan Medal from the American Astronomical Society.

Modern astronomy and planetary science stand on the verge of making some of the most profound discoveries ever achieved in the exploration of the cosmos. Historian and author Stephen Pyne has called this era the “third great Age of Exploration.” In the first age, Renaissance explorers such as Magellan, Columbus, and Vespucci discovered a so-called New World here on our own planet, mapping new continents and circumnavigating the globe in the sailing ships of the fifteenth and sixteenth centuries. In the second great Age of Exploration, seventeenth- to nineteenth-century Enlightenment explorers such as Cook, Lewis and Clark, and Powell pushed our exploration deep into those frontiers, discovering and documenting the details of new lands and peoples. At the same time, the scientific giants of the Enlightenment–Galileo, Brahe, Kepler, Copernicus, and Newton–helped us learn how we could eventually explore realms beyond our earthly home. The Scientific Revolution of the nineteenth to twentieth century propelled rocketry pioneers such as God .  .  .

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