Yoshifumi Saito

BepiColombo Mio (previously called MMO: Mercury Magnetospheric Orbiter) was successfully launched by Ariane 5 from Kourou, French Guiana on October 20, 2018. The Mercury Plasma/Particle Experiment (MPPE) is a comprehensive instrument package onboard Mio spacecraft used for plasma, high-energy particle and energetic neutral atom measurements. It consists of seven sensors including 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). Significant efforts were made pre-flight to calibrate all of the MPPE sensors at the appropriate facilities on the ground. High voltage commissioning of MPPE analyzers was successfully performed between June and August 2019 and in February 2020 following the completion of the low voltage commissioning in November 2018. Although all of the MPPE analyzers are now ready to begin observation, the full service performance has been delayed until Mio’s arrival at Mercury. Most of the fields of view (FOVs) of the MPPE analyzers are blocked by the thermal shield surrounding the Mio spacecraft during the cruising phase. Together with other instruments on Mio including Magnetic Field Investigation (MGF) and Plasma Wave Investigation (PWI) that measure plasma field parameters, MPPE will contribute to the comprehensive understanding of the plasma environment around Mercury when BepiColombo/Mio begins observation after arriving at the planet Mercury in December 2025.

©2017. American Geophysical Union. All Rights Reserved. The time resolution of low-energy charged particle measurements is becoming higher and higher. In order to realize high time resolution measurements, a 1-D circular delay line anode has been developed as a high-speed microchannel plate (MCP) anode. The maximum count rate of the 1-D circular delay line anode is around 1 × 107/s/360°, which is much higher than the widely used resistive anode, whose maximum count rate is around 1 × 106/s/360°. In order to achieve much higher speeds, an MCP anode with application-specific integrated circuit (ASIC) has been developed. We have decided to adopt an anode configuration in which a discrete anode is formed on a ceramic substrate, and a bare ASIC chip is installed on the back of the ceramic. It has been found that the anode can detect at a high count rate of 2 × 108/s/360°. Developments in both delay line and discrete anodes, as well as readout electronics, will be reviewed.

At similar to 25 km altitude over magnetic anomalies on the Moon, the deceleration of the solar wind ions, acceleration of the solar wind electrons parallel to the magnetic field, and heating of the ions reflected by magnetic anomalies were simultaneously observed by MAP-PACE on Kaguya. Deceleration of the solar wind ions was observed for two major solar wind ion compositions: protons and alpha particles. Deceleration of the solar wind had the same Delta E/q (Delta E: deceleration energy, q: charge) for both protons and alpha particles. In addition, the acceleration energy of the electrons was almost the same as the deceleration energy of the ions. This indicates the existence of an anti-moonward electric field over the magnetic anomaly above the altitude of Kaguya. The reflected ions were observed in a much larger area than the area where magnetic field enhancement was observed. These reflected ions had a higher temperature and lower bulk velocity than the incident solar wind ions. This suggests the existence of a non-adiabatic dissipative interaction between solar wind ions and lunar magnetic anomalies below Kaguya.

MAP-PACE (MAgnetic field and Plasma experiment-Plasma energy Angle and Composition Experiment) on SELENE (Kaguya) has completed its similar to 1.5-year observation of low-energy charged particles around the Moon. MAP-PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measured the distribution function of low-energy electrons in the energy range 6 eV-9 keV and 9 eV-16 keV, respectively. IMA and IEA measured the distribution function of low-energy ions in the energy ranges 7 eV/q-28 keV/q and 7 eV/q-29 keV/q. All the sensors performed quite well as expected from the laboratory experiment carried out before launch. Since each sensor has a hemispherical field of view, two electron sensors and two ion sensors installed on the spacecraft panels opposite each other could cover the full 3-dimensional phase space of low-energy electrons and ions. One of the ion sensors IMA is an energy mass spectrometer. IMA measured mass-specific ion energy spectra that have never before been obtained at a 100 km altitude polar orbit around the Moon. The newly observed data show characteristic ion populations around the Moon. Besides the solar wind, MAP-PACE-IMA found four clearly distinguishable ion populations on the day-side of the Moon: (1) Solar wind protons backscattered at the lunar surface, (2) Solar wind protons reflected by magnetic anomalies on the lunar surface, (3) Reflected/backscattered protons picked-up by the solar wind, and (4) Ions originating from the lunar surface/lunar exosphere.

Mercury is one of the least explored planets in our solar system. Until the recent flyby of Mercury by MESSENGER, no spacecraft had visited Mercury since Mariner 10 made three flybys: two in 1974 and one in 1975. In order to elucidate the detailed plasma structure and dynamics around Mercury, an orbiter BepiColombo MMO (Mercury Magnetospheric Orbiter) is planned to be launched in 2013 as a joint mission between ESA and ISAS/JAXA. Mercury Plasma Particle Experiment (MPPE) was proposed in order to investigate the plasma/particle environment around Mercury. MPPE is a comprehensive instrument package for plasma, high-energy particle and energetic neutral atom measurements. It consists of seven sensors: two Mercury electron analyzers (MEA1 and MEA2). Mercury ion analyzer (MIA), Mercury 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). Since comprehensive full three-dimensional simultaneous measurements of low to high-energy ions and electrons around Mercury as well as measurements of energetic neutral atoms will not be realized before BepiColombo/MMO's arrival at Mercury, it is expected that many unresolved problems concerning the Mercury magnetosphere will be elucidated by the MPPE observation. (C) 2008 Elsevier Ltd. All rights reserved.

Interaction between the solar wind and objects in the solar system varies largely according to the settings, such as the existence of a global intrinsic magnetic field and/or thick atmosphere. The Moon's case is characterized by the absence of both of them. Low energy ion measurements on the lunar orbit is realized more than 30 years after the Apollo period by low energy charged particle analyzers MAP-PACE on board SELENE(KAGUYA). MAP-PACE ion sensors have found that 0.1%similar to 1% of the solar wind protons are reflected back from the Moon instead of being absorbed by the lunar surface. Some of the reflected ions are accelerated above solar wind energy as they are picked-up by the solar wind convection electric field. The proton reflection that we have newly discovered around the Moon should be a universal process that characterizes the environment of an airless body. Citation: Saito, Y., et al. (2008), Solar wind proton reflection at the lunar surface: Low energy ion measurement by MAP-PACE onboard SELENE (KAGUYA), Geophys. Res. Lett., 35, L24205, doi:10.1029/2008GL036077.

MAP-PACE (MAgnetic field and Plasma experiment-Plasma energy Angle and Composition Experiment) is one of the scientific instruments onboard the SELENE (SELenological and ENgineering Explorer) satellite. PACE consists of four sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measure the distribution function of low-energy electrons below 15 keV, while IMA and IEA measure the distribution function of low energy ions below 28 keV/q. Each sensor has a hemispherical field of view. Since SELENE is a three-axis stabilized spacecraft, a pair of electron sensors (ESA-S1 and S2) and a pair of ion sensors (IMA and IEA) are necessary for obtaining a three-dimensional distribution function of electrons and ions. The scientific objectives of PACE are (1) to measure the ions sputtered from the lunar surface and the lunar atmosphere, (2) to measure the magnetic anomaly on the lunar surface using two ESAs and a magnetometer onboard SELENE simultaneously as an electron reflectometer, (3) to resolve the Moon-solar wind interaction, (4) to resolve the Moon-Earth's magnetosphere interaction, and (5) to observe the Earth's magnetotail.