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S. Dout\'e (IGPP UCLA), R. Lopes-Gautier, R. Carlson (JPL), B. Schmitt (CNRS LPG), L. Soderblom (USGS Flagstaff), Galileo NIMS Team
We analyse a collection of hyperspectral images of Io acquired by the Near Infrared Mapping Spectrometer (NIMS) of Galileo during the orbits G2 to E16. This analysis principally leads to the geographical distribution and physical characterization of SO2 frost deposits over \approx 2/3 of Io's surface. These deposits are excellent tracers of volcanic emission, atmospheric transportation, condensation, metamorphism, irradiation and sublimation, \ldots occuring throughout the SO2 cycle. We mainly study images with the highest spectral resolution (0.024 \micron) and spatial resolution (100 km to 350 km). First, we propose a very simple local surface representation of Io with patches of solid SO2 and other sulfur-bearing compounds. Second, we assess the mean photometric behavior of the SO2 frost using a sequence of spectra at two different locations over a large range of phase angles. Third, a more systematic inversion of the hyperspectral images is achieved based on the previous simple representation together with an original system of spectro-image modeling [1]. As a result, we produce two global mosaics that map SO2 frost coverage and mean grain size. SO2 rich or poor regions on one hand and fine or coarse grain regions on the other are defined and described. Then we correlate the two mosaics to distinguish four different SO2 physical units. For each, we establish a connection to different SO2 cycle phenomena. In particular, the link with the hot-spot distribution and activity type [2][3] is thoroughly investigated. In summary we obtain some clues about Io's volcanic activity, thermal flux and atmosphere.
[1] Douté, S. and Schmitt B. 1998. \emph{J. Geophys. Res.} \textbf{103}, pp. 31,367-31,390. [2] McEwen, A. S., and 14 colleagues 1998. \emph{Icarus} \textbf{135}, pp. 181-219. [3] Lopes-Gautier, R. M. C., and 12 colleagues 1999. Active volcanism on Io : Global distribution and variations in activity. \emph{Icarus}, in press.
The author(s) of this abstract have provided an email address for comments about the abstract: sdoute@igpp.ucla.edu