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W. D. Smythe, R. Lopes-Gautier, L. W. Kamp (JPL/CALTECH), L. A. Soderblom (USGS), A. G. Davies, R. W. Carlson (JPL/CALTECH), Galileo NIMS Team
The NIMS instrument on Galileo has detected numerous hotspots during the Galileo prime mission and the Galileo Europa mission. Most of the hotspots detected by NIMS exhibit single color-temperatures in the range of 350 to 1000 K, temperatures that are above the NIMS minimum detectable temperature of about 180K for filled pixels. Combined data from NIMS, SSI, and ground-based observations have shown that at least 29 hot spots are persistent over periods of one year or more. Persistent hotspots and active plumes are concentrated towards latitudes lower than 30 degrees. Determination of the heat flow from hotspots, and the relative contribution of persistent hotspots, permits assessment of whether persistent hotspots represent a significant fraction of the total heat flow, and are therefore relevant to understanding heat transport below the surface. Though NIMS cannot measure all of Io's heat flow (over half of which occurs at temperatures below 180K), the pattern of power output measured at all hotspots (which contribute about one third of the total heat flow) should represent the distribution of total heat flow at the surface.
The power output of hotspots varies temporally and spatially. Power output maps from NIMS data allows us to assess whether the greatest power output measured in the NIMS wavelength range correlates spatially with the location of persistent hotspots and plumes. Observations of Io in darkness taken by NIMS were used to make the thermal output maps. These thermal maps accentuate hot spots that are difficult to detect by other means. The results so far cover the longitude range 40W to 260W. In this range the hotspots that have the highest thermal output are Amirani/Maui, Altjirra, and Pele/Pillan. The highest thermal output occurs at latitudes lower than 60, which is consistent with the deposition of tidal energy above the mantle.