Charged particle signatures of the diamagnetic cavity of comet 67P/Churyumov–Gerasimenko

Abstract

One of the scientific objectives of the Rosetta mission is to investigate the diamagnetic cavity of comet 67P/Churyumov–Gerasimenko. We employed combined data of several instruments of the Rosetta Plasma Consortium (RPC) to identify and study diamagnetic cavity crossing events. Using electron data from the Ion Electron Sensor (IES) to complement the Magnetometer (MAG) data enabled us to work out a search criterion for the cavity crossing events based on a unique signature we identified in the electron spectrum. Although this search criterion is insufficient to find all the cavity events, we were able to find an abundance of more than one hundred cavity crossings in the data obtained in the summer of 2015. This unexpectedly high number of events allowed us to study their common features, as well as the shape and extent of the diamagnetic cavity in the terminator plane. The results suggest that in the summer of 2015 there was a cavity around comet 67P, which had a highly variable outer boundary. We present the effects of the diamagnetic cavity on the thermal and suprathermal electron and suprathermal ion content of the plasma, and also the probable mechanisms responsible for these charged particle signatures.