[P-CG19] 惑星大気圏・電磁圏

[PCG19-08] MPPE Observations Near BepiColombo's First Closest Approach to Mercury: Preliminary Results

*原田 裕己¹、斎藤 義文²、相澤 紗絵³、André Nicolas³、Persson Moa³、Delcourt Dominique⁴、Hadid Lina⁴、Fraenz Markus⁵、横田 勝一郎⁶、三宅 亙⁷、Fedorov Andréi³、Penou Emmanuel³、Katra Bruno⁴、Barthe Alain³、Sauvaud Jean-André³、松田 昇也⁸、村上 豪² (1.京都大学、2.宇宙科学研究所、3.IRAP, CNRS-UPS-CNES、4.LPP-CNRS-Sorbonne Université-Ecole Polytechnique、5.Max-Planck-Institute for Solar System Research、6.大阪大学、7.東海大学、8.金沢大学)

キーワード：水星、磁気圏、ベピ・コロンボ、みお

We report on preliminary results of in-depth analyses of ion and electron data obtained by the Mercury Plasma Particle Experiment (MPPE) onboard BepiColombo Mio near its first closest approach to Mercury. Prior to BepiColombo, a lack of high-time resolution measurements of low-energy ions and electrons hindered our ability to fully elucidate the dynamics and structure of Mercury's magnetosphere, which is known for its short time scales and small spatial dimensions. During the first Mercury flyby, Mio successfully obtained high-time resolution data of low-energy ions and electrons, unravelling the rich dynamics and structures of Mercury's magnetosphere. Here we focus on the MPPE observations at low altitudes below ~1000 km, and we utilize a magnetospheric magnetic field model (Korth et al., 2017) to infer the global and local magnetic fields, thereby properly contextualizing the particle observations. The observed signatures include the co-presence of hot (~keV/q) and cold (<~300 eV/q) ions around the midnight, significant ion flux depletion when the instrument field of view is covered by the loss cone predicted from the model, and quasi-periodic (~30 sec) flux enhancements of ~1-10 keV electrons with energy dispersion on dawn-side closed field lines. We discuss characteristics, interpretation, and implications of these particle observations by making a comparison with Mariner 10 and MESSENGER observations.