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H.U. Keller, Yu.V. Skorov (Max-Planck-Institut für Aeronomie), G.N. Markelov (Atos Origin Engeneering Services B.V.)
A Direct Simulation Monte Carlo (DSMC) method is used to model low density axisymmetric gas flows in the innermost coma region. We consider various types of "activity" (and spotted) both for a spherical and non-spherical nucleus at different heliocentric distances. The corresponding boundary conditions at the nucleus surface are determined from a self-consistent thermal model of a cometary nucleus developed by the authors (Davidsson and Skorov, Icarus, 2002). New model features are the absorption of the irradiation within the uppermost layers of the pores, kinetic treatment of gas transport into porous ice, the return gas fluxes from the coma, and temperature dependent condensation and sublimation coefficients. Fields of density, different types of temperature and velocity are calculated by parallel computer implementation of the kinetic model. The comparison with the results of fluid dynamics simulation is done where it is possible. We show that the innermost coma is sensitive to the nucleus shape as well as to the variations of local gas production rates. At the same time, small topography features produce only small coma "disturbances". In general spatial structures of the innermost coma (both gas and dust) are a result of interactions of gas flows sublimated from different surface regions. We conclude that the nucleus shape plays the major role in interpretation of innermost coma along with physical properties of nucleus.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.