Analysis of multiscale structures at the quasi-perpendicular Venus bow shock

Results from Solar Orbiter’s first Venus flyby

¹ Swedish Institute of Space Physics (IRF), Uppsala, Sweden
e-mail: andrew.dimmock@irfu.se
² Space and Plasma Physics, Department of Physics and Astronomy, Uppsala University, Uppsala 75120, Sweden
³ LPP, CNRS, Ecole Polytechnique, Sorbonne Université, Observatoire de Paris, Université Paris-Saclay, Palaiseau, Paris, France
⁴ Johns Hopkins Applied Physics Lab, Laurel, MD 20723, USA
⁵ Division of Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm 11428, Sweden
⁶ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 Place Jules Janssen, 92195 Meudon, France
⁷ Space Sciences Laboratory, University of California, Berkeley, CA, USA
⁸ Physics Department, University of California, Berkeley, CA, USA
⁹ LPC2E, CNRS, 3A avenue de la Recherche Scientifique, Orléans, France
¹⁰ Université d’Orléans, Orléans, France
¹¹ CNES, 18 Avenue Edouard Belin, 31400 Toulouse, France
¹² Technische Universität Dresden, Helmholtz Str. 10, 01187 Dresden, Germany
¹³ Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czech Republic
¹⁴ Space Research Institute, Austrian Academy of Sciences, Graz, Austria
¹⁵ Astronomical Institute of the Czech Academy of Sciences, Prague, Czech Republic
¹⁶ Radboud Radio Lab, Department of Astrophysics, Radboud University, Nijmegen, The Netherlands
¹⁷ Imperial College London, South Kensington Campus, London SW7 2AZ, UK

Received: 31 March 2021
Accepted: 1 February 2022

Abstract

Context. Solar Orbiter is a European Space Agency mission with a suite of in situ and remote sensing instruments to investigate the physical processes across the inner heliosphere. During the mission, the spacecraft is expected to perform multiple Venus gravity assist maneuvers while providing measurements of the Venusian plasma environment. The first of these occurred on 27 December 2020, in which the spacecraft measured the regions such as the distant and near Venus magnetotail, magnetosheath, and bow shock.

Aims. This study aims to investigate the outbound Venus bow shock crossing measured by Solar Orbiter during the first flyby. We study the complex features of the bow shock traversal in which multiple large amplitude magnetic field and density structures were observed as well as higher frequency waves. Our aim is to understand the physical mechanisms responsible for these high amplitude structures, characterize the higher frequency waves, determine the source of the waves, and put these results into context with terrestrial bow shock observations.

Methods. High cadence magnetic field, electric field, and electron density measurements were employed to characterize the properties of the large amplitude structures and identify the relevant physical process. Minimum variance analysis, theoretical shock descriptions, coherency analysis, and singular value decomposition were used to study the properties of the higher frequency waves to compare and identify the wave mode.

Results. The non-planar features of the bow shock are consistent with shock rippling and/or large amplitude whistler waves. Higher frequency waves are identified as whistler-mode waves, but their properties across the shock imply they may be generated by electron beams and temperature anisotropies.

Conclusions. The Venus bow shock at a moderately high Mach number (∼5) in the quasi-perpendicular regime exhibits complex features similar to the Earth’s bow shock at comparable Mach numbers. The study highlights the need to be able to distinguish between large amplitude waves and spatial structures such as shock rippling. The simultaneous high frequency observations also demonstrate the complex nature of energy dissipation at the shock and the important question of understanding cross-scale coupling in these complex regions. These observations will be important to interpreting future planetary missions and additional gravity assist maneuvers.