Electron bombardment of Europa

Energetic electrons trapped in Jupiter's magnetic field are a principal sou rce of energy for driving chemistry on the surface of Europa. Here we show that energetic (10 keV-10 MeV) electrons precipitate primarily on the trail ing hemisphere, and we give the spatial distribution of the dose-rate depos ited in Europa's surface. Based on this we propose that energetic electrons are a primary agent in determining the hemispherical differences in Europa 's albedo, which have been attributed to differences in the incident ion fl ux. We compare the spatial distribution in the dose-rate deposited by the e nergetic electrons to the spatial distribution in the hydrate (likely froze n, hydrated sulfuric acid) determined by Galileo's near-infrared mapping sp ectrometer. This comparison supports the idea that radiolysis by the energe tic electrons contributes significantly to producing the hydrate.