[P-CG19] Planetary Magnetosphere, Ionosphere, and Atmosphere

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

*Yuki Harada¹, Yoshifumi Saito², Sae Aizawa³, Nicolas André³, Moa Persson³, Dominique Delcourt⁴, Lina Hadid⁴, Markus Fraenz⁵, Shoichiro Yokota⁶, Wataru Miyake⁷, Andréi Fedorov³, Emmanuel Penou³, Bruno Katra⁴, Alain Barthe³, Jean-André Sauvaud³, Shoya Matsuda⁸, Go Murakami² (1.Kyoto University, 2.ISAS, JAXA, 3.IRAP, CNRS-UPS-CNES, 4.LPP-CNRS-Sorbonne Université-Ecole Polytechnique, 5.Max-Planck-Institute for Solar System Research, 6.Osaka University, 7.Tokai University, 8.Kanazawa University)

Keywords:Mercury, Magnetsophere, BepiColombo, Mio

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.