By the time it has descended below the water clouds, the increasing pressure will exceed the strength of some Probe components. Engineers expect the Probe to have completed its mission, exhausted its battery power, and been crushed by the atmospheric pressure before the 20-bar level is reached. Lifeless, it will then sink on into the thick, hot lower atmosphere of Jupiter. [Illustration: During its two years in orbit, the Galileo Orbiter will carry out many investigations of the planet, the Galilean satellites, and the Jovian magnetosphere. Repeated close flybys of the satellites are used to modify and shape the orbit to provide additional flybys at an optimum viewing geometry. Initially, the orbit is a long loop that extends in the general direction of the sunset side of Jupiter. The orbit is then contracted, and the encounters with the satellites rotate it behind the planet for a long excursion into the magnetotail late in the tour.] Beyond Galileo After Galileo, the future cannot be predicted. Perhaps there will no longer be a program of planetary exploration. But if humanity still has the vision to seek a future in the stars, there will surely be other Jupiter missions. Perhaps the next mission will concentrate on Jupiter itself. Probes could be built to withstand pressures as high as several hundred bars, feeling their way deep into the murky depths of the planet. Or a hot-air balloon could be deployed from a probe to carry instruments for long-term studies of the atmosphere. A number of proposals have also been made for additional satellite missions, including orbiters or landers for Ganymede and Callisto. Or perhaps it will be desirable to land a vehicle on one of the satellites and collect a sample and return it to Earth for laboratory analysis. Whatever the future holds, it is clear that the Pioneer and Voyager missions blazed the path to Jupiter and beyond. The little Pioneers proved that it could be done, and the Voyagers expanded their vision, exploring and discovering new worlds more remarkable and exciting than anyone could have imagined. APPENDIX A PICTORIAL MAPS OF THE GALILEAN SATELLITES These maps were prepared for the Voyager Imaging Team by the U.S. Geological Survey in cooperation with the Jet Propulsion Laboratory, California Institute of Technology and the National Aeronautics and Space Administration. Copies are available from Branch of Distribution, U.S. Geological Survey, 1200 South Eads Street, Arlington, VA 22202, and Branch of Distribution, U.S. Geological Survey, Box 25286, Federal Center, Denver, CO 80225. Preliminary Pictorial Map of Callisto Atlas of Callisto 1:25,000,000 Topographic Series Jc 25M 2RMN, 1979 I-1239