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K.J. Kossacki (MPI for Aeronomie, Inst. of Geophysics of Warsaw University), W.J. Markiewicz (MPI for Aeronomie), Y. Skorov (MPI for Aeronomie, Keldysh Inst. of Appl. Mathematics,), N.I. Koemle (Space Research Inst. of Austrian Academy of Sci.)
In simulations of evolution of cometary nuclei it is commonly assumed that the coefficients of sublimation and condensation of the volatiles are both equal to one. However, the laboratory investigation of water ice samples under cometary-like conditions (Kossacki et al., 1997) suggests, that the sublimation flux calculated with the Hertz-Knudsen formula and the above assumption is nearly an order of magnitude too high. A similar conclusion can be drawn from the results of various experiments on growth from vapour phase and sublimation of ice crystals (Lamb and Scott, 1972; Beckmann and Lacmann, 1982; Sei and Gonda, 1989). These results imply that the sublimation coefficient can be as low as 0.1. The above coefficients depend on various parameters such as temperature, concentration of surface impurities as well as deviation of the vapour pressure from that of the phase equilibrium. In this work we discuss the temperature dependence of both of these coefficients. We also propose an empirical formula to fit the temperature dependence. This new formulation is also used to analyse the implications for the thermal conductivity of a porous cometary-like ice.
The author(s) of this abstract have provided an email address for comments about the abstract: kjkossac@linmpi.mpg.de