The sublimation coefficient of water ice: influence on the temperature and outgassing of Comet 67P/C-G.

In most published works dealing with evolution of cometary nuclei, the sublimation rate of ices is calculated with simple Hertz-Knudsen equation. This formulation, derived from the kinetic theory of gases, ignores microphysical processes which determine the sublimation rate. To correctly account for these processes the modified Herz-Knudsen equation must include temperature dependent sublimation coefficient. Including this temperature dependence we find, that the temperature below dust mantle is most sensitive to the value of the sublimation coefficient when the mantle is coarse grained,while the sublimationrate is most affected when the mantle is fine grained. Most importantly, we also find that derivation of the temperature below the dust mantle from the measured water production rate ignoring temperature dependence of the sublimation coefficient can lead to an underestimate of the sub-dust temperature by more than 10 K.