Life in the Cosmos Revisited

The quest for life beyond Earth has become a major driving force in current astronomical research and space exploration. Whether this involves looking for fossil or extant evidence of microbial life on Mars or potential life on outer Solar System water bodies, biosignatures from exoplanets, or SETI, the underlying questions are the same: "Is life common or rare in the Universe?" and perhaps even more compelling: "Are we alone?" Since, for the first time in human history, we may actually get answers to these questions, this article reviews some of the key issues and considerations involved.