Energetic ions in the Venusian system: Insights from the first Solar Orbiter flyby

¹ Johns Hopkins Applied Physics Lab, Laurel, MD 20723, USA
e-mail: Robert.Allen@jhuapl.edu
² Space Research Group, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain
³ Institut für Experimentelle und Angewande Physik, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany
⁴ Swedish Institute of Space Physics (IRF), Uppsala, Sweden
⁵ Imperial College, London, UK
⁶ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁷ LPP, CNRS, Ecole Polytechnique, Sorbonne Université, Observatoire de Paris, Université Paris-Saclay, Palaiseau, Paris, France
⁸ Space Research Institute, Austrian Academy of Sciences, Graz, Austria
⁹ CNR/ISTP – Istituto per la Scienza e Tecnologia dei Plasmi, Via Amendola 122/D, 70126 Bari, Italy
¹⁰ Space Sciences Laboratory, University of California, Berkeley, CA, USA
¹¹ Physics Department, University of California, Berkeley, CA, USA
¹² Now at DSI Datensicherheit GmbH, Rodendamm 34, 28816 Stuhr, Germany
¹³ LPC2E, CNRS, 3A avenue de la Recherche Scientifique, Orléans, France
¹⁴ Université d’Orléans, Orléans, France
¹⁵ Now at Deutsches Elektronen-Synchrotron (DESY), Platanenallee 6, 15738 Zeuthen, Germany
¹⁶ CNES, Toulouse, France
¹⁷ Now at German Aerospace Center (DLR), Department of Extrasolar Planets and Atmospheres, Berlin, Germany
¹⁸ Technische Universität Dresden, Dresden, Germany
¹⁹ Now at Max-Planck-Institute for Solar System Research, Göttingen, Germany
²⁰ Institute of Atmospheric Physics of the Czech Academy of Sciences, Prague, Czech Republic
²¹ Astronomical Institute of the Czech Academy of Sciences, Prague, Czech Republic
²² Now at Univ. Colorado/LASP, Boulder, CO, USA
²³ Department of Space and Plasma Physics, School of Electrical Engineering and Computer Science, Royal Institute of Technology, Stockholm, Sweden
²⁴ Research Institute for Mathematics, Astrophysics and Particle Physics Radboud University, Nijmegen, The Netherlands

Received: 13 March 2021
Accepted: 30 April 2021

Abstract

The Solar Orbiter flyby of Venus on 27 December 2020 allowed for an opportunity to measure the suprathermal to energetic ions in the Venusian system over a large range of radial distances to better understand the acceleration processes within the system and provide a characterization of galactic cosmic rays near the planet. Bursty suprathermal ion enhancements (up to ∼10 keV) were observed as far as ∼50R_V downtail. These enhancements are likely related to a combination of acceleration mechanisms in regions of strong turbulence, current sheet crossings, and boundary layer crossings, with a possible instance of ion heating due to ion cyclotron waves within the Venusian tail. Upstream of the planet, suprathermal ions are observed that might be related to pick-up acceleration of photoionized exospheric populations as far as 5R_V upstream in the solar wind as has been observed before by missions such as Pioneer Venus Orbiter and Venus Express. Near the closest approach of Solar Orbiter, the Galactic cosmic ray (GCR) count rate was observed to decrease by approximately 5 percent, which is consistent with the amount of sky obscured by the planet, suggesting a negligible abundance of GCR albedo particles at over 2 R_V. Along with modulation of the GCR population very close to Venus, the Solar Orbiter observations show that the Venusian system, even far from the planet, can be an effective accelerator of ions up to ∼30 keV. This paper is part of a series of the first papers from the Solar Orbiter Venus flyby.