The giant planets and their satellites, systems individually of interest to astronomers, geophysicists, and geologists, become even more fascinating when studied collectively. Data from spacecraft missions, in particular, observations by the two Voyager spacecraft, have augmented significantly the evidence on which studies in comparative planetology rely.
Much can be learned from such studies, and examples of productive investigations abound. Tidal stress imposed on satellites locked into resonant orbits is now recognized as an important mechanism for internal heating of satellites. The relative importance of solar and internal heating and gravitational and centrifugal forces as influences on atmospheric circulation is being established by analysis of systems representing a substantial range of critical parameters. The surfaces of Galilean satellites can be read as records of early solar system evolution, and the imprinted evidence is being painstakingly deciphered. Some of these efforts help us to understand our own planet, its weather, and its surface, better. Others just tell us more about where we fit in a broader picture. All are interesting.