[P-PS04] Mercury Science and Exploration

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

*Yuki Harada¹, Yoshifumi Saito², Lina Hadid³, Dominique Delcourt³, Sae Aizawa³, Mathias Rojo⁴, Nicolas André⁴, Moa Persson⁵, Markus Fraenz⁶, Shoichiro Yokota⁷, Andréi Fedorov⁴, Wataru Miyake⁸, Emmanuel Penou⁴, Alain Barthe⁴, Jean-André Sauvaud⁴, Bruno Katra³, Shoya Matsuda⁹, Go Murakami² (1.Kyoto University, 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.Osaka University, 8.Tokai University, 9.Kanazawa University)

Keywords:Mercury, magnetosphere, ions, BepiColombo

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.