BepiColombo second Mercury flyby : Ion composition measurements from the Mass Spectrum Analyzer (MSA)

Dominique Delcourt (1, 2) , Lina Hadid (3) , Yoshifumi Saito (4) , Markus Fränz (5) , Shoichiro Yokota (6) , Björn Fiethe (7) , Christophe Verdeil (8) , Bruno Katra (1) , Frédéric Leblanc (1) , Henning Fischer (5) , Yuki Harada (9) , D. Fontaine (3) , Norbert Krupp (5) , Harald Michalik (7) , Jean-Marie Illiano (3) , Jean-Jacques Berthelier (10) , Harald Krüger (5) , Go Murakami (4) , Shoya Matsuda (11)

1 LPP - LPP - Laboratoire de Phonétique et Phonologie - UMR 7018
2 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
3 LPP - Laboratoire de Physique des Plasmas
4 ISAS - Institute of Space and Astronautical Science
5 MPS - Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research
6 Osaka University [Osaka]
7 IDA - Institute of Computer and Network Engineering [Braunschweig]
8 IRAP - Institut de recherche en astrophysique et planétologie
9 Kyoto University
10 HELIOS - LATMOS
11 KU - Kanazawa University

On June 23rd 2022, BepiColombo performed its second gravity assist maneuver (MFB2) at Mercury. Just like the first encounter with Mercury that took place on October 1st 2021, the spacecraft approached the planet from dusk-nightside to dawn-dayside down to an extremely close distance (within about 200 km altitude from the planet surface). Even though BepiColombo is in a so-called “stacked configuration” during cruise, meaning that the instruments cannot be fully operated yet, these instruments can still make interesting observations. Particularly, despite their limited field-of-view, the particle sensors allow us to get a hint on the ion composition and dynamics very close to the planet well before the forthcoming orbit insertion around Mercury in December 2025. In this study, we present observations of the Mass Spectrum Analyzer (MSA) at Mercury during MFB2. MSA is part of the low energy sensors of the Mercury Plasma Particle Experiment (MPPE) consortium (PI: Y. Saito), which is a comprehensive instrumental suite for plasma, high-energy particle and energetic neutral atom measurements (Saito et al., 2021) onboard the Mercury Magnetospheric Orbiter (Mio). MSA is a “reflectron” time-of-flight spectrometer that provides information on the plasma composition and the three-dimensional distribution functions of ions with energies up to ~ 38 keV/q and masses up to ~ 60 amu (Delcourt et al., 2016). In this study, we show that both H+ and He2+ ions in the 1-10 keV range are present throughout the innermost magnetosphere near closest approach. In addition, during this MFB2 sequence, MSA observations provide evidences of He+ ions with energies of several hundreds of eVs. These ions likely originate from the planet exosphere and are rapidly circulated within the magnetosphere. During the outbound sequence of MFB2, MSA measurements also reveal copious amounts of keV protons of solar wind origin that propagate upstream after being reflected from the bow shock.

Domaines: Planète et Univers [physics]

Dominique Delcourt, Lina Hadid, Yoshifumi Saito, Markus Fränz, Shoichiro Yokota, et al.. BepiColombo second Mercury flyby : Ion composition measurements from the Mass Spectrum Analyzer (MSA). EGU General Assembly 2023, Apr 2023, Vienna (Austria), Austria. pp.EGU23-3369, ⟨10.5194/egusphere-egu23-3369⟩. ⟨insu-04018529⟩