The scenic tour of the Venusian magnetosheath by BepiColombo

The Mercury-bound BepiColombo mission passed by Venus for a second gravity assist maneuver (GAM) on the 10^th of August, 2021. During the GAM, the plasma instrumentation on board the two spacecraft Mercury Magnetosphere Orbiter (MMO, JAXA), and Mercury Planetary Orbiter (MPO, ESA), which are stacked together during cruise before orbit insertion at Mercury in 2025, made measurements of the Venusian plasma environment. The entire passage was spent in the Venusian magnetosheath; from the entering of the inbound bow shock at around 12:30 UT, near 8 Rv from the planet, to the exit though the outbound bow shock near the subsolar point at 14:00 UT. This meant that it crossed several different subregions of the magnetosheath, which could be successfully measured and characterised by a combination of the many different plasma instruments on board the MMO and MPO spacecrafts of the BepiColombo mission.

In addition, one day before the Venus GAM for BepiColombo, the Solar Orbiter spacecraft performed a GAM at Venus, with a trajectory after the gravity assist leading upstream of Venus. As a result, the Solar Orbiter provided measurements of the solar wind conditions upstream of Venus during the BepiColombo GAM. Shifting the Solar Orbiter measurements with one hour showed a good correlation between the measurements of the Interplanetary Magnetic Field (IMF) by the two missions (when both were outside of the Venusian bow shock). Therefore, we conclude that Solar Orbiter was connected along the same Parker Spiral arm as Venus during the BepiColombo GAM, and the Solar Orbiter can be used as an upstream solar wind monitor.

Through the combination of the MPPE (Mercury Plasma/Particle Experiment) instrument package onboard MMO, the SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) instrument package and magnetometer onboard MPO, together with the upstream monitor by Solar Orbiter PAS (Proton Alpha Spectrometer) and magnetic field instruments, we have characterized and analysed the subregions of the Venusian magnetosheath. In this presentation we will give an overview of these observations and discuss the larger context of the results.