Hybrid modeling of cometary plasma environments

II. Remote-sensing of a cometary bow shock

¹ School of Electrical Engineering, Aalto University, Maarinkatu 8, PO Box 15500, 00760 Aalto, Finland
e-mail: markku.alho@aalto.fi
² Department of Physics, University of Oslo, PO Box 1048, Blindern, 0316 Oslo, Norway
e-mail: cyril.simon.wedlund@gmail.com
³ Swedish Institute of Space Physics, PO Box 812, 981 28 Kiruna, Sweden
⁴ Department of Computer Science, Luleå University of Technology, Electrical and Space Engineering, Kiruna 981 28, Sweden
⁵ Finnish Meteorological Institute, PO Box 503, 00101 Helsinki, Finland
⁶ Department of Climate and Space Sciences and Engineering, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143, USA

Received: 14 December 2018
Accepted: 27 February 2019

Abstract

Context. The ESA Rosetta probe has not seen direct evidence of a fully formed bow shock at comet 67P/Churyumov–Gerasimenko (67P). Ion spectrometer measurements of cometary pickup ions measured in the vicinity of the nucleus of 67P are available and may contain signatures of the large-scale plasma environment.

Aims. The aim is to investigate the possibility of using pickup ion signatures to infer the existence or nonexistence of a bow shock-like structure and possibly other large-scale plasma environment features.

Methods. A numerical plasma model in the hybrid plasma description was used to model the plasma environment of a comet. Simulated pickup ion spectra were generated for different interplanetary magnetic field conditions. The results were interpreted through test particle tracing in the hybrid simulation solutions.

Results. Features of the observed pickup ion energy spectrum were reproduced, and the model was used to interpret the observation to be consistent with a shock-like structure. We identify (1) a spectral break related to the bow shock, (2) a mechanism for generating the spectral break, and (3) a dependency of the energy of the spectral break on the interplanetary magnetic field magnitude and bow shock standoff distance.