At the heart of a provocative narrative that stretches from Renaissance Italy to the moons of Jupiter is the father of modern science: Galileo Galilei. To the inhabitants of the Jovian moons, Galileo is a revered figure whose actions will influence the subsequent history of the human race. From the summit of their distant future, a charismatic renegade named Ganymede travels to the past to bring Galileo forward in an attempt to alter history and ensure the ascendancy of science over religion. And if that means Galileo must be burned at the stake, so be it. From Galileo's heresy trial to the politics of far-future Jupiter, Kim Stanley Robinson illuminates the parallels between a distant past and an even more remote future--in the process celebrating the human spirit and calling into question the convenient truths of our own moment in time.