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C. B. Phillips (SETI Institute), A. S. McEwen, L. P. Keszthelyi, P. E. Geissler (LPL), D. P. Simonelli (Cornell), M. Milazzo (LPL), Galileo Imaging Team
Lava flows and plumes are the two main types of volcanic activity that resurface Io. We have used the Galileo Io dataset to document these changes at a number of Io’s active volcanic centers, using an iterative coregistration and ratioing technique. 3.5 years of global-scale observations have allowed us to observe the interconnections between plume activity, hotspot activity, and new surface deposits at a number of volcanic centers on Io. Activity has been detected at previously unknown locations, and we have established timescales for the formation and alteration of various color units, such as red plume deposits and green coatings on caldera floors. Red material has faded on a timescale of less than a year, and a green coating has formed on a caldera over a time period of about 3 months.
We have used three independent techniques to estimate Io's resurfacing rate: surface changes, the lack of impact craters, and global heat release. 1) Change detection maps, which illustrate the percentage of the surface newly covered by either plume deposits or lava flows, show that areal resurfacing is dominated by plume deposits, but volume resurfacing is dominated by lava flows. Estimates of the global average resurfacing rate from these change maps range from 0.4 to 14 cm/year, assuming a flow thickness of 1 to 10 meters. 2) The minimum average resurfacing rate required to explain the lack of impact craters on Io's surface is about 0.02 cm/year. 3) The maximum average resurfacing rate by high-magnesium (komatiitic) lavas, if they dominate the observed Io heat flux, is about 0.7 cm/year. Basaltic lavas would produce a rate of 1.3 cm/year, and sulfur flows 12.5 cm/year. Thus, the net resurfacing rate on Io must be >0.02 cm/year, and could be as high as a few cm/year, depending on the mix of lava flow types.
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