Three-dimensional magnetohydrodynamic model of the interaction between the solar wind and cometary atmospheres

A magnetohydrodynamic (MHD) model of the interaction between the solar wind and an expanding gas flow issuing from a comet nucleus is presented. The processes of photoionization of the neutral component of the comet matter and the resonance charge exchange between charged and neutral particles are taken into account, together with the interplanetary magnetic field effect. The adequacy of the single-fluid MHD approximation in describing the plasma flow with different temperatures of the components is shown. The model is numerically realized on the basis of the higher-order Godunov method using an approximate solution of the arbitrary MHD discontinuity breakdown problem. The results of a numerical investigation of the plasma and magnetic field parameters in the vicinity of a comet are presented for the conditions corresponding to the flyby of several spacecraft near comet Halley in March 1986 and the expected fly-round of comet Churyumov-Gerasimenko by the Rosetta spacecraft in 2015.