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. We've learned a lot in those years, and planetary scientist David Grinspoon is well prepared to explore this field with a new generation of readers. In Lonely Planets, Grinspoon 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?

In accessible, lively prose, and using the topic of extraterrestrial life as a mirror with which to view human beliefs, evolution, history, and aspirations, Grinspoon takes readers on a three-part journey.

History is an overview of our expanding awareness of other planets, from the observations of seventeenth-century natural philosophers to modern-day space exploration. It traces the history of our ideas on alien life to the earliest days of astronomy, and shows how these beliefs have changed with humanity's evolving self-image.

Science tells the story of cosmic evolution and the evolution of life on Earth. Here, Grinspoon disputes the recent "Rare Earth hypothesis, " which argues that Earth is unique for sprouting advanced life-forms, maintaining instead that life is likely to be well adapted to a wide variety of planets. He questions conventional assumptions of what is required for a planet to come to life, scrutinizing current ideas and evidence for life on Mars, Venus, and the moons of Jupiter, and challenging readers to think about other life-forms that may exist on other worlds.

Belief discusses the limits of our abilities to conceptualize or communicate with intelligent aliens living on planets circling distant stars. Grinspoon speculates on what intelligent life might become, eventually, on Earth and elsewhere, and the implications, both scientific and philosophical, of these far-future evolutionary possibilities.

Written with authority and edge, and rich in personal, often amusing anecdotes, Lonely Planets explores the shifting boundary between planetary science and naturalphilosophy and reveals how the search for extraterrestrial life unites our spiritual and scientific quests for connection with the cosmos.