Electron moments derived from the Mercury Electron Analyzer during the cruise phase of BepiColombo

¹ IRAP, CNRS-UPS-CNES, Toulouse, France
e-mail: mathias.rojo@irap.omp.eu
² University of Tokyo, Kashiwa, Japan
³ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
⁴ University of Pisa, Pisa, Italy
⁵ Department of Space and Climate Physics, University College of London, London, UK
⁶ Department of Earth and Space Science, Graduate School of Science, Osaka University, Osaka, Japan
⁷ Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Braunschweig, Germany
⁸ Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften, Graz, Austria
⁹ Faculty of Natural Sciences, Department of Physics, Imperial College London, London, UK
¹⁰ Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris-Diderot, Sorbonne Paris-Cité, France
¹¹ Swedish Institute of Space Physics, Uppsala, Sweden

Received: 31 August 2023
Accepted: 14 November 2023

Abstract

Aims. We derive electron density and temperature from observations obtained by the Mercury Electron Analyzer on board Mio during the cruise phase of BepiColombo while the spacecraft is in a stacked configuration.

Methods. In order to remove the secondary electron emission contribution, we first fit the core electron population of the solar wind with a Maxwellian distribution. We then subtract the resulting distribution from the complete electron spectrum, and suppress the residual count rates observed at low energies. Hence, our corrected count rates consist of the sum of the fitted Maxwellian core electron population with a contribution at higher energies. We finally estimate the electron density and temperature from the corrected count rates using a classical integration method. We illustrate the results of our derivation for two case studies, including the second Venus flyby of BepiColombo when the Solar Orbiter spacecraft was located nearby, and for a statistical study using observations obtained to date for distances to the Sun ranging from 0.3 to 0.9 AU.

Results. When compared either to measurements of Solar Orbiter or to measurements obtained by HELIOS and Parker Solar Probe, our method leads to a good estimation of the electron density and temperature. Hence, despite the strong limitations arising from the stacked configuration of BepiColombo during its cruise phase, we illustrate how we can retrieve reasonable estimates for the electron density and temperature for timescales from days down to several seconds.