It's been nearly four decades since Carl Sagan first addressed the general public from a scientist's perspective, confronting the possibility of extraterrestrial life. David Grinspoon, a planetary scientist who has helped to shape modern planetary exploration, brings the subject to a new generation of readers with his reflections on the most recent developments in astrobiology, including NASA's search for life on Mars. In Lonely Planets, he investigates the big questions: How widespread are life and intelligence in the cosmos? Is life on Earth an accident or in some sense the "purpose" of this universe? And how can we, working from the Earth-centric definition of "life," even begin to think about the varieties of life-forms on other planets?Using the topic of extraterrestrial life as a mirror with which to view human beliefs, evolution, history, and aspirations, Grinspoon provides an authoritative scientific narrative of cosmic evolution, along with provocative ruminations on how we fit into the story of the universe. An accessible, lively blend of science, history, philosophy, and personal narrative, Lonely Planets reveals how the search for extraterrestrial life unites our spiritual and scientific quests for connection with the cosmos.