Microphysical modeling of comets and planetesimals

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Motivated by our recent results from laboratory experiments on the formation of macroscopic highporosity dust aggregates with physical properties matching those observed in comets and by new close-up observations of cometary nuclei, this proposal intends to derive at a detailed description of the physical processes in the near-surface layers of a cometary nucleus and the transition region between nucleus and coma. In this project, we will perform so far unfeasible laboratory experiments on the gas permeability and thermal properties of cometary analogs as well as on the dynamical interactions of loosely-bound dust grains with rarefied-gas flows. These experimental results will then be used to calibrate our new thermophysical model of the cometary surface and the transition region between nucleus and coma, which will consist of an improved morphological description of the outer layers of the cometary nucleus, an improved treatment of mass and energy transfer in the nucleus and in the coma, and a model of the dust acceleration in the vicinity of the cometary surface. As a side-effect, we will also arrive at a better description of the dust-dust interaction in protoplanetary disks, which involves very similar physical properties as those present in comets. By combining the expertise of an experimental (IGEP) and a theoretical/observational (MPS) group, our model will encompass the complete picture that we currently have of the physical processes close to a cometary nucleus and of protoplanetary precursors of comets, the planetesimals/cometesimals.