Introduction: A Multidisciplinary Approach to Habitability

Developments during the early years of space exploration provided particular impetus toward articulating the concept of habitable planets beyond Earth. One of these developments was the collective results of the life-detection experiments conducted by the Viking missions, which demonstrated that an improved understanding of environmental context was crucial to the search for evidence of life on Mars. Another development was the expansion of the search for extraterrestrial intelligence and Frank Drake’s articulation in 1961 of his famous Drake Equation (Drake and Sobel 1992), which identifies the parameters that collectively estimate the probability of detecting intelligent life elsewhere. A meeting entitled “Life in the Universe” was held in 1979 at NASA Ames Research Center (Billingham 1981). In addition to articulating topics in astronomy and biology, the participants disseminated key factors that sustain habitable planetary environments. They addressed, among other factors, stellar and orbital influences, planetary accretion and early development, atmospheres, climate, and the origins and evolution of continents and oceans. An additional strong impetus