Adaptive Optics Mapping of Io's Volcanism in the Thermal IR (3.8 μm)

Abstract Two opposite hemispheres of Io were observed on October 20 and 21, 1996, through an L′ broadband filter, using the high-resolution capability of the Adaptive Optics (AO) system implemented on the ESO 3.6-m telescope at La Silla, Chile. These observations, performed at thermal wavelengths when Io is in daylight, have been carefully processed to improve the sharpness of the initial, diffraction-limited, images. The myopic deconvolution process used ( idac ) achieved an angular resolution estimated to be 0.15 arcsec, corresponding to a spatial resolution of ∼570 km on Io's disc at the time of the observations. The final images show a number of bright features which have been compared with the Galileo/NIMS data, the only data set with a comparable resolution available for the anti-Jovian side of the satellite as well as its Jupiter-facing side. Our maps of the hot spot distribution are quite consistent with the Galileo data. The Jupiter-facing side is dominated by emission from Loki, which accounts for ∼25% of the total hot spot emission from that side (and 45% of that we were able to resolve and identify), although Loki was in a phase of decreasing activity (but not yet quiescent), as derived from ground-based monitoring observations. A few more hot sources are detected, including Pele–Pillan. The other hemisphere is characterized by a large number of moderately bright hot spots which are distributed around Bosphorus Regio. These preliminary observations fully demonstrate the capabilities of an AO system coupled with a thermal camera to monitor the volcanic activity of Io, in terms of morphology as well as thermal output. These monitoring capabilities will become especially important when the Galileo mission ends.

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