BepiColombo Mio Observations of Low‐Energy Ions During the First Mercury Flyby: Initial Results

Abstract

Driven by the intense solar wind in the inner heliosphere, Mercury's magnetosphere is known to be small and dynamic. Mercury's weak dipole magnetic field of 190 nT-𝐴𝐴 𝐴𝐴 3 𝑀𝑀 (Anderson et al., 2012), where R M is Mercury's radius, and high solar wind dynamic pressures at Mercury's orbit (∼5-10 times higher at 0.31-0.47 AU than those at 1 AU) result in small spatial dimensions of the magnetosphere with an average subsolar standoff distance of 1.45 R M (Winslow et al., 2013). Consequently, time scales of magnetospheric dynamics driven by the solar wind are considerably short at Mercury (e.g., Siscoe et al., 1975). Our understanding of Mercury's magnetosphere has been greatly advanced thanks to the two previous missions to Mercury, Mariner 10 and MESSENGER, but there remain many open questions as to the plasma sources, energy and mass transport, and particle acceleration processes in Mercury's magnetosphere, and their coupling to the exosphere, surface, and interior of the planet (J.

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

“…The inbound magnetopause (MP) crossing occurred at 23:08:30 UTC (Supplementary Fig. 1 ), whereas the outbound MP and bow shock (BS) crossing occurred at 23:41:00 UTC and 23:45:30 UTC, respectively 16 , as also reported from other ion observations by the Search for Exospheric Refilling and Emitted Natural Abundances instrument onboard BepiColombo 17 . Due to a telemetry data gap, no inbound BS crossing was directly measured by MEA1, MEA2, or MIA.…”

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

“…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).…”

“…The plasma instrument on MPO, SERENA, indicates these boundary crossings to be encountered at 23:10 and 23:40, respectively (Orsini et al, 2022). Observations of the low energy ions during MSB1 show similar values of the inbound and outbound magnetopause at 23:10 and 23:41 (Harada et al, 2022). 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.…”

Ultra‐Low Frequency Waves in the Hermean Magnetosphere: On the Role of the Morphology of the Magnetic Field and the Foreshock

“…An especially interesting question is the possible role of the precipitating particles and/or foreshock waves for the generation of the ULF waves in Mercury's magnetosphere. Ion measurements during MFB1 have revealed rapid flux fluctuations within just a few seconds near the closest approach (Harada et al., 2022). However, until now, no ULF wave observations have been published from MFB1.…”