at Ganymede's polar cap, the latter being comparable to radiogenic energy input. Rates of change in optical reflectance and molecular composition on Europa, and on Ganymede's polar cap, are strongly driven by energy from irradiation, even in relatively young regions. Irradiation of nonice materials can produce SO 2 and CO 2 , detected on Callisto and Europa, and simple to complex hydrocarbons. Iogenic neutral atoms and meteoroids deliver negligible energy ∼10 4-5 keV (cm 2 -s) −1 but impacts of the latter are important for burial or removal of irradiation products. Downward transport of radiation produced oxidants and hydrocarbons could deliver significant chemical energy into the satellite interiors for astrobiological evolution in putative sub-surface oceans.

Anodes of elemental carbon may be discharged in a galvanic cell using a molten carbonate electrolyte, a nickel-foam anode-current collector, and a porous nickel air cathode to achieve power densities of 40-100 mW/cm 2 . We report cell and anode polarization, surface area, primary particle size and a crystallization index for nine particulate carbon samples derived from fuel oil, methane, coal, charred biological material and petroleum coke. At 800 °C, current densities of 50-125 mA/cm 2 were measured at a representative cell voltage of 0.8 V. Power densities for cells with two carbon-anode materials were found to be nearly the same on scales of 2.8-and 60 cm 2 active area. Constant current operation of a small cell was accompanied by constant voltage during multiple tests of 10-30 hour duration. Cell voltage fell off after the carbon inventory was consumed. Three different cathode structures are compared, indicating that an LLNL fabricated porous nickel electrode with <10 µm pores provides improved rates compared with nickel foam with 100-300 µm pores.Petroleum coke containing substantial sulfur and ash discharges at a slightly lower rate than purified petroleum coke. The sulfur leads to degradation of the anode current collector over time. A conceptual model for electrochemical reactivity of carbon is presented which indicates the importance of (1) bulk lattice disorder, which continually provides surface reactive sites during anodic dissolution and (2) electrical conductivity, which lowers the ohmic component of anode polarization.

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Europa's orbit in the radiation environment of Jupiter is reviewed as is the influence of the neutral gas torus on the surface weathering of that moon. Data and fits to charged particle intensities in the 1-keV to the tens-of-MeV energy range are provided near Europa. Leading/trailing hemisphere differences are highlighted. Effects of charged particles on the surface of Europa, such as sputtering and chemistry, are reviewed.