Kazushi Asamura

Abstract Using Arase satellite observations, this study provides a comprehensive statistical analysis of ions (H⁺, He⁺, O⁺) and electron contributions to the total ring current pressure during storms with two different drivers. The results demonstrate the effect of different solar wind drivers on the composition, energy distribution, and spatial characteristics of the ring current. Using 32 CIR‐ and 30 Interplanetary Coronal Mass Ejection (ICME)‐driven storms, we characterize the ring current pressure evolution during the prestorm, main, early‐recovery, and late‐recovery storm phases as a function of magnetic local time and L‐shell. In CIR‐driven storms, H⁺ ions are the dominant (∼70%) contributor to the total ring current pressure during main/early recovery phases and increasing to ∼80% during late recovery. In contrast, the O⁺ pressure (E = 20–50 keV) response is significantly stronger in ICME‐driven storms contributing ∼40% to the overall pressure during the main/early recovery phases and even dominate (∼53%) in certain MLT sectors. Additionally, ICME‐driven storms tend to have peak pressure at lower L‐shells (L ≈ 3–4), while CIR‐driven storms show pressure peaks at slightly higher L‐shells (L ≈ 4–5). Interestingly, electron pressure also plays a notable role in specific MLT sectors, contributing ∼18% (03–09 MLT) during the main phase of CIR‐driven storms and ∼11% (21–03 MLT) during ICME‐driven storms. The results highlight that the storm time electron pressure plays a crucial role in the ring current buildup. Another noteworthy feature of this study is that Arase's fine‐energy resolution and broad coverage enable a detailed investigation of energy‐dependent ring current dynamics.

Abstract The interaction between lunar magnetic anomalies and the solar wind plasma creates unique structures known as “lunar mini‐magnetospheres,” which reflect and partially shield the lunar surface from impinging solar wind protons. Using data from the Sub‐KeV Atom Reflecting Analyzer onboard Chandrayaan‐1, we produce new surface maps of energetic neutral atom (ENA) and reflected proton emissions. We show that solar wind proton precipitation can be reduced by up to 80% inside magnetic anomalies and increased by up to 50% on scales larger than 1,000 km around magnetic anomalies. The morphology of these proton precipitation enhancement and depletion regions varies differently as a function of upstream solar wind dynamic pressure for small, isolated anomalies compared to the large South Pole‐Aitken (SPA) magnetic cluster. In contrast to small magnetic anomalies, which are compressed and less effective at shielding the surface from the solar wind at high dynamic pressures, the SPA magnetic cluster creates a large “mini‐magnetosphere” that alters proton precipitation patterns on global‐scales (>1,000 km) inside and around the cluster. We show that this behavior may result from the interaction between protons reflected by the SPA magnetic anomaly cluster and the solar wind.

Abstract The mass spectrum analyzer (MSA) is one of the instruments onboard MMX and observes the interaction between the Martian moons (Phobos and Deimos) and the solar wind as well as the material transport between Mars and its moons. MSA consists of an ion mass spectrum analyzer and a magnetometer. The objective of the magnetometer, MSA-MG, is to measure the magnetic field at the MMX position to trace the motion of the ions. We defined the requirements for the performance of the MSA-MG and designed the instrument to meet them. It is confirmed that MSA-MG as a unit has the required characteristics by the ground performance test and calibration. One of the essential calibration parameters, artificial bias in the data, must be determined by analyzing the flight data. To improve the accuracy of the determined bias, efforts to remove the magnetic noise from other components onboard MMX are essential.

Abstract An ion energy mass spectrum analyzer was developed for the Martian Moons eXploration (MMX) mission to measure the three-dimensional velocity distribution function and mass profile of low-energy ions around the Mars-Moon system. The hemispheric field-of-view (FOV) is acquired by a pair of angular scanning deflectors, and the energy/charge and mass/charge are determined for each ion by an electrostatic analyzer and a linear-electric-field (LEF) time-of-flight (TOF) analyzer, respectively, with an enhanced mass resolution of $$m/\Delta m\sim 100$$ . The ion analyzer, together with magnetometers, constitutes the mass spectrum analyzer (MSA), one of the scientific instruments on board the MMX spacecraft. This paper describes the instrumentation of the ion analyzer, and results of the performance tests of its flight model (FM).

Abstract We developed an ultra-compact analog front-end for time-of-flight (TOF)-type ion mass spectrometers using application-specific integrated circuit (ASIC) technology. The front-end amplifies signals generated by the microchannel plate of the TOF-type ion mass spectrometer, uses a comparator to distinguish signals from noise, and generates detection signals compatible with low-voltage differential signaling (LVDS) standards for subsequent digital processing. Laboratory experiments with the developed ASIC, employing ion beam irradiation, demonstrated that the developed analog front-end has sufficient timing resolution. Temperature tests indicated minimal variation in the detectable input level of the front-end with temperature changes. The experimental results indicated that the developed ASIC front-end is suitable for TOF-type ion mass spectrometry in space applications. Graphical Abstract