JOVIAN SYSTEM DATA ANALYSIS PROGRAM PROPOSAL SUMMARY

The proposed work will utilize the many primary Galileo Orbiter flybys of the Galilean satellites (Io, Europa, Ganymede and Callisto) to extract information on the charge states of energetic magnetospheric ions interacting with the satellites, and on limits for internal magnetic field sources, particularly for Io and Ganymede. Hot plasma ions of oxygen,sodium, and sulfur at keV to MeV energies are thought to arise from neutral winds of these elements blowing out from the Io torus into the outer jovian magnetosphere, where they are partially ionized into low charge states by ambient radiation (UV, plasma electrons, charge exchange with other ions), picked up and accelerated to 100 keV energies by the corotating planetary magnetic field, and transported with further acceleration up to 100 MeV energies by various magnetospheric processes into the inner magnetosphere of Jupiter. Composite measurements of ion energy spectra and anisotropies are compiled from Galileo Energetic Particle Detector (EPD) and Heavy Ion Counter (HIC) data to define the hot plasma environments near the orbit of each satellite and during close encounter flybys. Numerical codes for tracking of charged particle motions in the planetary and satellite magnetic fields are used to reconstruct the directional distributions of ions incident on the spacecraft. On initial approach to a satellite the depletions of the lowest charge state and more energetic ions, which have relatively large gyroradii of the order of the satellite radius or larger, are detected first, and higher charge state interactions are observed closer to the satellite. Modeling the positional and directional variations in ion flux during the flyby for each ion type (e.g., oxygen and sulfur) yields constraints on the distributions of ion charge states and also on limits for internal magnetic fields for Io and Ganymede, for which some controversy still remains on whether an internal field source exists or whether plasma effects near the satellites are responsible for the observed magnetic field variations. Even local magnetic fields induced in subsurface conducting layers (e.g., a salty ocean for Europa and now Callisto) by the jovian planetary field may produce detectable effects in lower energy hot plasma ions and electrons. The modeling of the ion interactions also yields more accurate information than previously available on global patterns of ion impacts on the surface of each satellite, which are used to model effects of the ionizing radiation on the outer ice layers. Irradiation effects include changes in molecular chemistry as the incident ions lose energy, implantation of iogenic sulfur ions, and erosion of the surfaces by ion sputtering. Such effects can visibly alter the ice chemistry and reflectance properties on relatively short time scales in the jovian magnetospheric radiation environment. This may, for example, be relevant to the Galileo discovery of mineral salts on the trailing hemisphere (side opposite to orbital motion around Jupiter) of Europa, since the salts may have originally been minor constituents of volatile ices ejected from surbsurface layers (e.g., oceans). The proposed work is relevant to various NASA programs including mission support for the Galileo and continuing analyses of data from earlier explorations (Pioneer, Voyager, Ulysses) of the Jupiter magnetosphere and its interactions with the satellites. Findings on charge states may resolve open questions about the origins of the highest energy trapped ions and how such ions are accelerated. Efforts to provide unique new constraints on internal magnetic fields of the satellites are of considerable interest to NASA's planetary science programs in relation to understanding the internal dynamics and evolution of planets and their satellites. An Education and Public Outreach activity entitled "Interaction of Magnetospheric Particles Applied to Classroom Teaching (IMPACT)" is proposed to introduce high school physics students to basic theory and experiments for effects of magnetic fields as applied to hands-on activities with magnets and more easily visualized phenomena (e.g., polar aurorae, visual albedo asymmetries induced by corotating particle impacts on satellites, etc.) investigated by Galileo and earth-based observations of the jovian system. IMPACT will involve summer teacher interns in work on development of curricula and hands-on activities for different levels up through advanced physics at the high school and introductory undergraduate level. A Java-based Internet tool will be developed to assist in validation of research calculations for ion motions in magnetic fields and for potential usage in on-site and remote classroom situations.