THE INFLUENCE OF GRAIN SINTERING ON THE THERMOCONDUCTIVITY OF POROUS ICE

The aim of this work is to improve the method of calculating the therm oconductivity of porous ices and porous icy/rocky mixtures. The main i nterest are planetological applications, mostly for the physics of com ets as well as icy satellites. However, the results could-in modified form-also be applied to the Earth's glaciers. The present work is an e xtension of an existing model of thermoconductivity of porous ice give n by Steiner and Komle (Planet. Space Sci. 39, 507, 1991), which takes into account energy transport by gas and by contact points between gr ains, but with the simplifying assumption that the structure of the ma terial remains unchanged during thermal evolution. Now the sintering o f ice grains, which leads to a continuous growth of the grain-to-grain contact area (Hertz factor) is incorporated into the thermal evolutio n model. Example calculations illustrating the effect of grain sinteri ng on thermal evolution in different temperature ranges are performed, using initial and boundary conditions suitable to the geometry used i n the 'comet simulation' experiments described in Komle et al. (Planet . Space Sci. 39, 515, 1991; Planet. Space Sci. 40, 1311, 1992). It was found that the grain sintering process, which was commonly neglected in previous studies of the thermoconductivity of ice, may lead to sign ificant changes of the matrix conductivity on time scales of hours to days. Therefore it should also play an important role in the thermal h istory of comet nuclei and thus affect the gas and dust emission activ ity of comets.