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Electron dynamics at Mercury: acceleration, circulation and precipitation processes using a global fully-kinetic model

Abstract : Mercury is the only telluric planet of the solar system, other than Earth, with an intrinsic magnetic field. Thus, the Hermean surface is shielded from the impinging so- lar wind via an “Earth-like” magnetosphere. This magnetic cavity is however twenty times smaller than its counterpart at the Earth and Mercury occupies a large portion of this cavity. The relatively small extension of the Hermean magnetosphere enables us to model its interaction with the solar wind plasma using a global fully-kinetic model. Such modeling is crucial to interpret ongoing, and prepare future, observations of the joint ESA/JAXA BepiColombo mission. The goal of this work is to study the global electron dynamics in the Hermean magneto- sphere with a particular focus on charged particles acceleration, circulation and precipi- tation processes. The model used in this work is based on three-dimensional, implicit, full-PIC simula- tions of the interaction between the solar wind and Mercury’s dipole magnetic field. This model self-consistently includes plasma processes from the large planetary scale down to the electron scale. As a first result, we find a plasma current flowing at the magnetospheric boundaries (bow shock and magnetopause) with amplitude the order of thousands of nA/m2 dominated by electrons. Furthermore, in our simulations magnetic reconnection in the tail accelerates and heats electrons up to tens of keV in the case of southward interplanetary magnetic field (IMF). These electrons are ejected from the neutral line in the tail planet-ward in a substorm fashion. They start drifting dawn-ward around the planet forming a quasi- trapped population in the nightside and - eventually - a large fraction of those falls on the planet surface. We also show comparisons between our simulations and in-situ ob- servations by Mariner10 and BepiColombo space missions We argue that these electrons have been observed in-situ by Mariner10/PLS instrument during its first Mercury flyby around and after closest approach. A similar population, although fainter, have been ob- served by BepiColombo/MEA instrument in the nightside magnetosphere. To conclude, we show maps of electron precipitation on Mercury’s surface and discuss them in compar- ison with MESSENGER/XRS observations of Calcium X-ray fluorescence emission from the surface.
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https://hal-insu.archives-ouvertes.fr/insu-03768686
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Submitted on : Sunday, September 4, 2022 - 6:17:01 PM
Last modification on : Tuesday, September 6, 2022 - 3:24:40 AM

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  • HAL Id : insu-03768686, version 1

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Federico Lavorenti, Pierre Henri, Francesco Califano, Jan Deca, Sae Aizawa, et al.. Electron dynamics at Mercury: acceleration, circulation and precipitation processes using a global fully-kinetic model. Mercury 2022 Conference, Jun 2022, Orléans, France. ⟨insu-03768686⟩

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