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H.U. Keller, Yu.V. Skorov (Max-Planck-Institut für Sonnensystemforschung), G.N. Markelov (Atos Origin Engineering 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" (coherent and spotted) for a non-spherical nucleus at different heliocentric distances. Gas flows from nucleus area containing various morphological formations (such as flat-bottom craters and mesas) with reasonable topographical features are treated.
The corresponding boundary conditions at the nucleus surface are determined from a self-consistent thermal model of a cometary nucleus developed by 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 gas density, temperature and velocity are calculated by parallel computer implementation of the kinetic model. The qualitative comparison with the observational data obtained for comet Wild 2 by the Stardust space probe is done.
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 local 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 general nucleus shape as well as nucleus morphology play the major role in interpretation of innermost coma along with physical properties of nucleus.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.