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J. R. Spencer, J. A. Stansberry (Lowell Obs.), L. K. Tamppari (J.P.L.)
Europa's low crater density suggests that geological activity has continued to the present epoch (Chapman et al. 1997), leading to the possibility that current resurfacing events might be detectable by thermal infrared techniques. Thermal techniques are particularly attractive because excess thermal radiation from a resurfacing event may be detectable for many decades (VanCleve 1998). One very tentative identification of a 5-\mum brightening of Europa has already been reported in the literature (Tittemore and Sinton 1989).
We are looking for endogenic thermal anomalies on Europa via two techniques. Firstly, we are looking for hotspots in nighttime 17-50\mum maps of Europa made by the Galileo PPR instrument. None have been seen so far, with a preliminary upper limit of 14 km for the diameter of any hot spot warmer than 200 K in the areas mapped. Secondly, we are beginning a monitoring campaign at the NASA Infrared Telescope, Mauna Kea, looking for 3.8-4.8\mum thermal emission from Europa during Jupiter eclipse. We expect to be sensitive to any hot spot larger than 26 km in diameter that is warmer than 250 K. The groundbased technique is less sensitive than the Galileo technique, but the potential long timebase of observations will increase our chances of finding brief, bright, events.
References: Chapman et al. 1997, BAAS 29, 984. VanCleve 1998, Icarus, submitted. Tittemore and Sinton 1989, Icarus 77, 82-89.