Plasma environment of comet Churyumov-Gerasimenko 3D hybrid code simulations

Abstract

Recent measurements indicate the H2O production rate of comet Churyumov-Gerasimenko to be of the same order as for comet Wirtanen. From a plasma physical point of view, this classifies both comets as "weak comets", i.e. the plasma structures known form larger comets differ much from the MHD picture. We present two 3D hybrid model simulation results for Churyumov-Gerasimenko for heliocentric distances of 3.25 AU and 2.8 AU. We focus on the kinetic effects of the ions, which are retained by the hybrid model. The results should be directly applicable to the interpretation and prediction of data which will be obtained by the ROSETTA plasma instruments during the early encounter. It is found, that the "classical" plasma boundaries are not present at this early stage, because their characteristic scales are smaller than the gyroradius of the solar wind protons as well as the heavy ions. Moreover, complex particle energy distributions are found.