Global plasma-parameter simulation of Comet 67P/Churyumov-Gerasimenko approaching the Sun

Abstract

We simulate the evolution of the plasma environment of comet 67P/Churyumov-Gerasimenko (CG), which is the target comet of the European Space Agency's (ESA) Rosetta mission, as the comet approaches the Sun. The plasma environment is calculated in three dimensions with a hybrid plasma model. The model treats the dynamics of the solar wind protons and the cometary ions in the framework of the macroparticle approach while the electrons are treated as a massless, charge-neutralizing fluid. The simulation starts at 4.2 AU and finishes at 1.3 AU. The outgassing strength of the comet is calculated from a thermal nucleus model. The model accounts for heat conduction, heat advection, gas diffusion, sublimation, and condensation processes in a porous ice-dust matrix with moving boundaries. The movement of the boundaries (Stefan problem) is accounted for by a temperature remapping technique. The maxima of the cometary ion flux and of the magnetic field in the simulation domain are presented as functions of heliocentric distance. The bow shock (BS), the ion composition boundary (ICB), and the magnetic pileup boundary (MPB) position along the Sun-comet line as a function of heliocentric distance are also discussed. A comparison of the BS position with an analytical formula yields good agreement. The MPB and the ICB along the Sun-comet line coincide.