Io in the Infrared - Science Opportunities with the JIMO Mission

The Jupiter Icy Moons Orbiter (JIMO) presents an opportunity to greatly improve our understanding of the most dynamic body in the solar system. Io is the best place to study tidal heating of the Galilean moons, provides unique insights into Earth history and is a unique laboratory for basic planetary physics. Many important questions about Io remain after Galileo that cannot be addressed from Earth or Earth orbit, but could be answered by limited observing time from JIMO with the appropriate instrumentation. Here we outline objectives in the infrared. We discuss two major science issues that can be addressed with infrared observations from JIMO: Io's heat flow and surface chemistry. This would build on the results from the Galileo NIMS and PPR experi-ments. Tidal Heating: A major puzzle is that recent estimates (using ground-based and Galileo observations) are higher than predicted by steady-state tidal heating rates. It is necessary to understand why this is so on Io to properly understand tidal heating on Europa. We need high spatial resolution measurements of the spatial distribution of Io's thermal radiation and accurate measurements of its bolometric Io's surface chemistry: Io's surface chemistry is still largely unknown except for SO{_2}, which is ubiquitous on the surface. The composition of Io's very high temperature magma is unknown. Since surface areas not covered by SO{_2} are fairly small (a few km{^2}), infra-red spectroscopic observations at spatial resolutions around 1 km, which would be unique to JIMO, are needed. Two major limitations of the existing long wavelength coverage on Io are limited spatial coverage at high spatial resolution - particularly at high spectral resolution and limited coverage of the Jupiter facing hemisphere. The former prevents obtaining unmixed spectra of unique surface features (such as fresh flows) - and the latter has makes it difficult to interpret global behavior of Io. To understand Io, one needs to map Io at spatial resolutions better than one kilometer over the spectral range 0.8 to about 40 microns, and to obtain a reasonable spatial coverage at spectral resolutions high enough to measure isotopic fractionation. The spectral range includes iron bands (0.8-1.3 microns, mineral and volatiles bands (1-15 microns) and thermal measurements (0.8 to 40 microns). Most these needs could be met with limited observing time from JIMO, an-swering many of the important remaining questions about Io.