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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Oct 2020

16 Oct 2020

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This preprint is currently under review for the journal ANGEO.

Warm protons at comet 67P/Churyumov-Gerasimenko – Implications for the infant bow shock

Charlotte Goetz1,2, Herbert Gunell3,4, Fredrik Johansson5, Kristie LLera6, Hans Nilsson7, Karl-Heinz Glassmeier2, and Matthew G. G. T. Taylor1 Charlotte Goetz et al.
  • 1European Space Research and Technology Centre, European Space Agency, Keplerlaan 1, 2201AZ Noordwijk, the Netherlands
  • 2Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany
  • 3Department of Physics, Umeå University, 901 87 Umeå, Sweden
  • 4Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Avenue Circulaire 3, 1180 Brussels, Belgium
  • 5Institutet för Rymdfysik, Lägerhyddsvägen 1, Uppsala, Sweden
  • 6Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166, USA
  • 7Institutet för rymdfysik, Rymdcampus 1, Kiruna, Sweden

Abstract. Multiple plasma boundaries have been observed at comet 67P/Churyumov-Gerasimenko. Among them was an infant bow shock, an asymmetric structure in the plasma environment that separates the less disturbed solar wind from a plasma with warmer, slower protons. Rosetta crossings of the infant bow shock have so far only been reported for two days. Here, we aim to investigate this phenomenon further by focusing on the proton behaviour and surveying all of the Rosetta comet phase data. We find over 300 events that match the proton signatures at the infant bow shock. We investigate the properties of the plasma and magnetic field at this boundary and the location where it can be found. We find that the protons are preferentially detected at intermediate gas production rates with a slight trend towards larger cometocentric distances for higher gas production rates. The events can mostly be found in the positive convective electric field hemisphere. Both results agree well with simulations of the infant bow shock. The properties of the plasma are harder to constrain, but there is a trend towards higher electron flux, lower magnetic field, higher magnetic field power spectral density, and higher density in the region that contains the warm protons. This is in partial agreement with the previous IBS definitions, however it also indicates that the plasma and this structure are highly non-stationary. For future research, Comet Interceptor, with its multi-point measurements, can help to disentangle the spatial and temporal effects and give more clarity on the influence of changing upstream conditions on the movement of boundaries in this unusual environment.

Charlotte Goetz et al.

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Charlotte Goetz et al.

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Latest update: 27 Oct 2020
Publications Copernicus
Short summary
Boundaries in the plasma around comet 67P separate regions with different properties. Many have been identified, including a new boundary called an infant bow shock. Here, we investigate how the plasma and fields behave at this boundary and where it can be found. The main result is that the infant bow shock occurs at intermediate activity and intermediate distances to the comet. Most plasma parameters behave as expected, however some inconsistencies indicate that the boundary is non-stationary.
Boundaries in the plasma around comet 67P separate regions with different properties. Many have...