LABORATORY INVESTIGATION OF THE EVOLUTION OF COMETARY ANALOGS - RESULTS AND INTERPRETATION

The thermal and structural evolution of multicomponent ice/mineral sam ples due to surface radiative heating has been investigated experiment ally. The components of the samples were water ice, carbon dioxide ice , and dunite. Starting with originally homogeneous mixtures, we observ ed the sublimation of different volatiles under low pressure and low t emperature conditions. This process resulted in the formation of strat ified samples, containing clearly divided regimes with different chemi cal composition and cohesivity. A new computer model, developed along the lines of our previous work, is applied to provide a quantitative d escription of the observed temperature evolution and stratification wi thin the samples. These processes may play a key role in the formation of surface layers of cometary nuclei. Within the ROSETTA mission, sev eral already accepted experiments aim at a direct (in situ) investigat ion of just these near-surface layers on the nucleus of Comet P/Wirtan en. Therefore, both the rather generally applicable thermal model and the particular results of our laboratory experiments may provide usefu l support for the design of these experiments. (C) 1997 Academic Press .