[P-PS04] Mercury Science and Exploration

[PPS04-03] MIA Observations of Low-energy Ions During Mio's 4th and 6th Mercury Flybys: Preliminary Results

*原田 裕己¹、斎藤 義文²、Hadid Lina³、Delcourt Dominique³、相澤 紗絵³、Rojo Mathias⁴、André Nicolas⁴、Persson Moa⁵、Fraenz Markus⁶、横田 勝一郎⁷、Fedorov Andréi⁴、三宅 亙⁸、Penou Emmanuel⁴、Barthe Alain⁴、Sauvaud Jean-André⁴、Katra Bruno³、松田 昇也⁹、村上 豪² (1.京都大学理学研究科、2.ISAS, JAXA、3.LPP-CNRS-Sorbonne Université-Ecole Polytechnique、4.IRAP, CNRS-UPS-CNES、5.Swedish Institute of Space Physics, Uppsala、6.Max-Planck-Institute for Solar System Research、7.大阪大学、8.東海大学、9.金沢大学)

キーワード：水星、磁気圏、イオン、ベピ・コロンボ

MIA onboard the BepiColombo Mio spacecraft conducts low-energy ion observations around Mercury with a high time resolution and wide energy range. During the first three Mercury flybys in nearly equatorial flyby configurations, MIA detected (i) different properties of ion energy spectra in Mercury's magnetosphere for each of the three flybys, likely resulting from different solar wind conditions, (ii) rapid ion flux fluctuations with time scales down to a few seconds, implying short-time scale magnetotail dynamics, and (iii) relatively dense ions with energies <~100 eV/q even around midnight at low altitudes, suggesting transport of solar wind protons in the magnetotail. These observations highlight that our understanding of the variability, dynamics, and structure of Mercury's magnetosphere is still incomplete. Here, we present new MIA observations from the fourth and sixth Mercury flybys. These flyby configurations are distinctly different from the first three. Mio traversed high-latitude northern regions on nearly dawn-dusk and noon-midnight planes during the fourth and sixth flybys, respectively. We show characteristic ion structures observed by MIA, comparison with data obtained by other instruments on Mio, and preliminary interpretations thereof.