Launched in 1989, Project Galileo is NASA's most ambitious interplanetary mission to date. The Galileo spacecraft is scheduled to crash into Jupiter's turbulent atmosphere in September 2003, nearly nine years after it entered orbit around the mighty planet. During this time, Galileo made a number of startling discoveries and transmitted more than 6,000 images of Jupiter and its many moons.This book explores Jupiter's moons: Io, which simmers with more than 100 active cauldrons and spews lava fountains some 5,000 feet high; Europa, encrusted with salt-stained ice that may hide a once-living subterranean sea; Ganymede, the only moon in our solar system known to generate its own magnetic field; and Callisto, which may harbor a buried ocean and is one of the oldest and possibly unchanged places in our solar system; as well as Jupiter's so-called inner moons and thirty-two additional minor moons. It shows that the Jovian system is like none we know.