Structure and dynamics of the hermean magnetosphere revealed by electron observationsafter the first three Mercury flybys of BepiColombo, 50 years after Mariner 10.

The Mercury Electron Analyzer (MEA) obtained new electron observations during the first threeMercury swingbys (MSBs) by BepiColombo on 01 October 2021 (MSB1), 23 June 2022 (MSB2),and 19 June 2023 (MSB3). We identify the magnetospheric boundaries and describe the structure and dynamics of the electron populations observed in the various regions explored along the swingby trajectories. We compare and contrast our new BepiColombo electron observations with those obtained from the Mariner 10 Scanning Electron Spectrometer (SES) 50 years ago.A comparison to the averaged magnetospheric boundary crossings by MESSENGER indicatesthat the magnetosphere of Mercury was compressed during MSB1, close to its average stateduring MSB2, and highly compressed during MSB3. Our new MEA observations revealed asignificant dusk-dawn asymmetry in electron fluxes on the nightside magnetosphere, and ofstrongly fluctuating electrons with energies above 100s eV on the dawnside magnetosphere.Magnetospheric electron densities and temperatures were in the range of 10-30 cm and above a few 100s eV in the pre-midnight-sector, and in the range of 1-100 cm and well below 100 eV in the post-midnight sector, respectively.MEA electron observations of different solar wind properties encountered during the first threeMSBs revealed the highly dynamic response of the solar wind-magnetosphere interactions atMercury. A good match is found between the electron plasma parameters derived by MEA in the various regions of the Hermean environment with similar ones derived for a few cases from other instruments on board BepiColombo.