Abstract | The Mercury Plasma/Particle Experiment (MPPE) is a comprehensive instrument package on BepiColombo/Mio spacecraft for plasma, high-energy particle and energetic neutral atom measurements. It consists of 7 sensors: two Mercury Electron Analyzers (MEA1 and MEA2), Mercury Ion Analyzer (MIA), Mass Spectrum Analyzer (MSA), High Energy Particle instrument for electron (HEP-ele), High Energy Particle instrument for ion (HEP-ion), and Energetic Neutrals Analyzer (ENA). During the Venus and Mercury fly-bys most of the MPPE analyzers including MIA were turned on and made observation of Venus induced magnetosphere and Mercury Magnetosphere though most of the field of view of the MPPE analyzers were blocked by MOSIF (MMO Sunshield and Interface Structure) before arriving at Mercury in December 2025. MEA, MIA, MSA, HEP-ele, and ENA successfully made observations during Earth fly-by in April 2020, Venus fly-by #1 and Venus fly-by #2 in October 2020 and August 2021, respectively, and Mercury fly-by #1 in October 2021.
MIA that measures 3D phase space density of low energy ions between 15eV/q and 29keV/q was developed for understanding (1) structure of the Mercury magnetosphere, (2) plasma dynamics of the Mercury magnetosphere, (3) Mercury - solar wind interaction, (4) atmospheric abundances, structure, and generation/loss process, and (5) solar wind between 0.3 and 0.47 AU. In order to achieve these science objectives, MIA was designed to measure the three-dimensional distribution function of both solar wind ions around Mercury, and Mercury magnetospheric ions. After experiencing Earth fly-by and 1st Venus fly-by, the necessity of modifying the MIA flight software in MDP (Mission Data Processor) was identified. Although the output range of the onboard calculated ion velocity moment is limited, the definition of the output range was not optimum. The new software was successfully uploaded on 22 June 2021. MIA succeeded in observing low energy ions in the induced magnetosphere and ionosphere of Venus during Venus fly-by #2. MIA observed $\sim$ 20-second periodic low energy ion flux in the Mercury magnetosheath - magnetosphere boundary where magnetosheath ions and magnetosphere ions seem to co-exist. MIA also observed the similar ion signature that is usually observed in crossing the separatrix of the magnetic reconnection in the Earth’s magnetotail.
We are planning to turn on most of the MPPE analyzers including MIA during the future Mercury fly-bys scheduled in June 2022, June 2023, September 2024, December 2024 and January 2025. The observation with full performance of MIA will start after Mio's arrival at Mercury in December 2025. |
