In order to understand the physical and chemical processes which produce the tenuous planetary and planetary satellite (upper) atmospheres through interactions with their particle, field, and radiation environs, it is necessary to analyze remotely observed and spacecraft data with physically meaningful models. With this in mind, we have undertaken a coupled program of theoretical modeling and complementary data analysis regarding the global distributions of neutral and ionized gases in, and escape from, tenuous planetary atmospheres of Io and Europa. The theoretical models developed will have further applications to other tenuous atmospheres such as that of Pluto and Titan or the upper atmospheres of the terrestrial planets. Combi, Michael R. and Beebe, Reta (Technical Monitor) Goddard Space Flight Center ...