Billions of years ago, our nearest planetary neighbor, Venus, may have harbored lakes, oceans, and lifegiving habitats similar to those on the early Earth. Today, Venus spins slowly in a backward direction. It's a planet knocked upside down and turned inside out. Its burnedout surface is a global fossil of volcanic destruction, shrouded in a dense, toxic atmosphere. Scientists have come to see Venus as the alien planet “next door,” a laboratory for testing ideas about how planets evolve and the challenges they face in nurturing life. They are now unveiling daring new strategies to reach down to its hostile surface. From floating bases stationed high in Venus’ atmosphere, they hope to send down new generation probes to search for clues from a time when the planet was alive. How did Venus descend into this hellish state? And how did its sister planet, Earth, manage to survive?