Thermal conductivity and radiation processing of Mimas and Tethys leading hemisphere anomalies

Analysis of Cassini spectroscopy and photometry data revealed an anomalous region present on the leading edge of the Saturnian icy moons Mimas and Tethys. A lens shaped feature centered on the equator of the leading hemisphere of both Mimas and Tethys was seen clearly as a low IR/UV ratio compared to the surrounding surface [Schenk et al., 2011]. Additionally, a region of roughly the morphology exhibited an increased thermal conductivity [Howett et al., 2012]. The anomalous region closely matches the expected deposition profile of high energy >1 MeV) electrons traveling opposite to the thermal plasma [Paranicas et al., 2012]. It is thought that these electrons can explain the optical feature through increased scattering at UV wavelengths due to a higher concentration of light scattering defects in the icy regolith grains, as well as explain the increased thermal conductivity by increasing the effective contact area between adjacent ice grains through sintering. These hypotheses were tested by applying published heat flow models for porous regoliths to estimate relative grain properties necessary to explain the thermal conductivity differences, comparing the defect creation rate vs. optical depth, and applying numerical simulations to determine sintering effects in the porous water-ice regolith. The time-scale for the cementation to increase sufficiently is then compared with estimates of the regolith gardening rate to determine whether a steady state is maintained.