NASA's robot spacecraft Galileo began its long voyage to Jupiter more than six years and 2.3 billion miles ago. About 24 hours from now it will reach its destination. On arrival (December 7th, 1995), Galileo should become the first spacecraft to orbit around a gas giant planet and the first to drop a probe into a giant planet's dense atmosphere. In the above Hubble Space Telescope image, the predicted probe entry location is indicated by the arrow. If all goes well, the atmospheric probe will relay information about temperature, pressure, and composition for about an hour as it descends through Jupiter's clouds, while the orbiter will spend at least two years exploring the Jovian system. Along with advancing our knowledge of Jupiter and its environs, Galileo data is expected to reveal some of the secrets of the formation and evolution of the Solar System.