JOVIAN SYSTEM DATA ANALYSIS PROGRAM PROPOSAL SUMMARY

The overall objective of this project is to advance our understanding of the 3-D nature of the Iogenic plasma source created near the satellite at the time of the December 7, 1995 Galileo flyby of Io and to elucidate its relationship to the downstream Galileo plasma and magnetic field measurements and to the basic structure of the plasma torus. The Iogenic plasma source (pickup ions created by net mass-loading and charge exchange) is produced as Io's local and extended atmospheres undergo electron impact ionization and charge exchange reactions in the magnetosphere as well as photoionization. These pickup ions supply the plasma torus (the densest part of the magnetosphere) with an input of new ions, net mass, and energy. Observational data acquired by the Galileo Plasma Analyzer (PLS), Plasma Wave Subsystem (PWS), and Magnetometer (MAG) instruments along the downstream trajectory of the Galileo spacecraft during its Io flyby provide an invaluable collective data set for studying the spatial behavior and structures of the plasma and magnetic field near Io produced by the interaction of Io and the corotating plasma torus. Understanding the nature of the Iogenic plasma source is one of the key elements in these studies. To explore the plasma and magnetic field measurements near Io, we will combine (1) state-of-the-art neutral cloud models for atomic and molecular species (H, O, S, SO, SO2) including a Galileo plasma torus description to calculate the Iogenic plasma source and (2) an advanced magnetohydrodynamic model to simulate the plasma torus interaction with Io. We expect (1) to determine the relative strength and 3-D distributions for the net mass-loading and charge exchange rates and densities for different pickup ions and their abundances relative to the thermalized background ions and (2) to investigate the role of these pickup ions in Galileo measured spatial profiles for the plasma densities, flow velocity, temperatures, and magnetic field reductions near Io, in measured anisotropic ion velocity distributions, and in measured magnetic field time signatures for ion-cyclotron and mirror mode waves. To explore the basic structure of the Galileo flyby plasma torus ultimately produced by the Iogenic plasma source, both a 3-D empirical plasma torus model and a 2-D plasma torus transport model will be utilized. We expect to determine a Galileo plasma torus description upstream of Io, locate the plasma ribbon (densest part of the plasma torus) in the upstream Galileo plasma torus, and explore and compare the plasma ribbon in the plasma torus as a function of local time for both the Galileo and Voyager flyby times. The proposed research is expected to enhance significantly the scientific return for the Galileo prime mission. The primary goal of the Educational/Public Outreach proposal, in collaboration with the Museum of Science in Boston, is to develop a program for the fall or spring season show at the Charles Hayden Planetarium with a theme of "Planetary Atmospheres" or "Satellites of the Solar System".