EVOLUTION OF A POROUS H2O-CO2-ICE SAMPLE IN RESPONSE TO IRRADIATION

The thermal history and the chemical differentiation of a porous H2O-C O2-ice SaMPle is studied for four different examples. In the first two cases, the possible effect of a nonvolatile mantle covering the ice i s investigated. In examples 3 and 4 the influence of the average grain size and the Hertz factor, which determine the effective thermal cond uctivity of the ice, on the sample evolution are investigated. Our com putations show that both the amount of heating and the compositional e volution critically depend on the assumed ice material parameters and the presence of a mantle. The results are compared with other theoreti cal work and relevant experiments, and we found good agreement between experimental results and our theoretical predictions. Finally, some i mplications for comet nuclei and future spacecraft missions to comets are discussed.