Predictions to the Plasma Environment of Comet 67P/Churyumov-Gerasimenko

Abstract

In summer 2014 the European Rosetta mission arrived at comet 67P/Churyumov-Gerasimenko and will stay close to the comet during its orbit around the Sun. As the comet approaches the Sun a cometary atmosphere is formed which interacts with the solar wind. The Rosetta Plasma Consortium (RPC) will study this interaction and will perform measurements of various structures and boundaries within this environment. The aim of this thesis is to make predictions about the location of the various plasma structures and boundaries. These predictions are obtained by means of analytical models and numerical simulations, i.e. the A.I.K.E.F. code. In parallel the processes which lead to the plasma interaction and the structures in the cometary plasma environment are analysed. A first study of a weakly active comet far away from the Sun shows that at this activity level the interaction is dominated by the cometary pick-up ion tail. Furthermore, it is found that along this tail a repetitive Mach cone is triggered. In a second study the close vicinity of the comet is analysed. There the cometary pick-up ion tail and the footpoint of a Mach cone is found. In addition, a low frequency wave pattern at the comet is analysed and a first preliminary comparison to the RPC magnetometer data is conducted, in which a similarity to the waves in the hybrid simulations is observed. Close to the perihelion, the cometary activity will reach its maximum and the Mach cone will be transformed into a bow shock. Its position is analysed in a third study. A comparison reveals a major difference between the fluid models and the hybrid model concerning the instantaneous pick-up of the cometary ions. Due to the more realistic description of the pick-up in the hybrid model, the bow shock is much closer to the comet than expected before. In addition, a strong dependency of the bow shock position on the solar wind parameters is found. In the fourth study the innermost coma is analysed. For the first time ever, a global hybrid simulation is able to resolve this region sufficiently to allow for an investigation of the plasma boundaries in that region, i.e. the diamagnetic cavity and the cometary ionopause. A shift of the entire interaction region as well as of all related structures and boundaries therein away from the Sun-comet line is found. In addition, this study predicts the presence of three distinct cometary ion populations at the innermost boundaries.