**31st Annual Meeting of the DPS, October 1999**

*Session 30. Comet Nuclei II*

Contributed Oral Parallel Session, Tuesday, October 12, 1999, 2:00-3:30pm, Sala Pietro d'Abano
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## [30.08] Sublimation Coefficient of Water Ice

*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

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