JOVIAN SYSTEM DATA ANALYSIS PROGRAM PROPOSAL SUMMARY

We plan to use the Galileo PPR (Photopolarimeter-Radiometer) radiometric data on Io, together with improved thermal modeling, to develop improved constraints on the total volcanic heat flow from Io. Io's total endogenic heat flow is a critical constraint on geophysical models, particularly as current best estimates of heat flow are a factor of 2 or more higher than the greatest power achievable by tidal heating in steady-state, and there are problems with alternate, non-steady-state, models. The PPR instrument has obtained many global maps of Io's thermal emission in the 17-50 micron region, over a wide range of local times (including the first global measurements of Io's nighttime thermal emission), and provides longitude and time coverage complementary to Voyager's. We plan to use these unique data to better understand Io's total thermal radiation, particularly the passive component which must be understood in order to separate out the endogenic component. We will also use improved thermophysical models of the thermal emission from hot spots and the passive surface, constrained by both Galileo, Voyager IRIS, and groundbased observations, and improved bolometric albedo maps of Io provided by our collaborators from Galileo data, to refine our understanding of Io's passive thermal radiation and thus obtain an improved heat flow estimate. The improved knowledge of passive surface temperatures will also be useful for understanding volatile behavior on Io.