Direct evidence of substorm-related impulsive injections of electrons at Mercury

Abstract

Mercury’s magnetosphere is known to involve fundamental processes releasing particles and energy like at Earth due to the solar wind interaction. The resulting cycle is however much faster and involves acceleration, transport, loss, and recycling of plasma. Direct experimental evidence for the roles of electrons during this cycle is however missing. Here we show that in-situ plasma observations obtained during BepiColombo’s first Mercury flyby reveal a compressed magnetosphere hosts of quasi-periodic fluctuations, including the original observation of dynamic phenomena in the post-midnight, southern magnetosphere. The energy-time dispersed electron enhancements support the occurrence of substorm-related, multiple, impulsive injections of electrons that ultimately precipitate onto its surface and induce X-ray fluorescence. These observations reveal that electron injections and subsequent energy-dependent drift now observed throughout Solar System is a universal mechanism that generates aurorae despite the differences in structure and dynamics of the planetary magnetospheres.

Determining the Influence of the IMF and Planetary Magnetic Field Models on Mercury's Magnetosphere Along Spacecraft Trajectories of MESSENGER, BepiColombo and MPO

“…In another analysis of the plasma instrument observation onboard Mio, Aizawa et al. (2023) identified the inbound magnetopause crossing at 23:08:30 and the outbound magnetopause crossing at 23:41. While the modeled inbound magnetopause is outside of the shown time range, they are encountered at around 23:18 for the pnp and npp cases and at around 23:20 for the pnn and npn cases.…”

“…As the observed outbound magnetopause crossings align better with our model results for the pnn and npn cases (orange and purple), we infer that the upstream IMF likely had a negative B Z,IMF component which led to a higher magnetic field erosion of the dayside magnetopause. However, this estimation relies on a nominal upstream solar wind dynamic pressure, which the data analysis does imply (Aizawa et al., 2023; Griton et al., 2023; Harada et al., 2022; Orsini et al., 2022). Similar data analysis for the MSB2 maneuver are still in progress in the community, so we limit our analysis to that under nominal upstream dynamic pressure conditions, the modeled inbound magnetopause is located at around 9:22 for the pnp, pnn and npp cases (green, orange and pink) and at around 9:24 for the npn cases (purple).…”

Recent advances in the magnetic reconnection, dipolarization, and auroral processes at giant planets from the perspective of comparative planetology

“…The magnetosphere of Mercury is much smaller than the terrestrial magnetosphere; thus, in some extreme solar wind conditions, dayside magnetic reconnection can strip all closed magnetic field lines at the equator and form an equatorial cusp region (Slavin et al, 2010). Because of the lack of atmosphere and ionosphere, it is not expected to have auroral substorms and the associated magnetospheric processes, although similar energy deposits may be found (Aizawa et al, 2023).…”