Fully 3-dimensional calculations of dust mantle formation for a model of Comet 67P/Churyumov-Gerasimenko

A fully 3-dimensional implicit numerical model for comet nucleus evolution is presented, emphasizing dust mantle formation. A spherical configuration is considered with an initial composition of amorphous H2O ice and dust, taking into account a discrete dust-grain size distribution. The model is applied to Comet 67P/Churyumov-Gerasimenko, adopting its orbital elements, rotation period and rotation axis inclination. We find that the dust mantle thickness varies over the surface from 1 cm to about 10 cm (thus lower and higher than the diurnal skin-depth, respectively). The size distribution of ejected grains varies along the orbit and is steeper than the initial one adopted for the nucleus. The crystallization front advances inward in spurts, and its depth varies between 1 and several meters. We test the effect of the thermal conductivity on the surface temperature distribution and depths of the dust mantle and crystallization front.