BepiColombo at Mercury: Three Flybys, Three Magnetospheres

Abstract We examine the first three BepiColombo Mercury flybys Using data from the Miniature Ion Precipitation Analyzer (MIPA), an ion mass analyzer in the Search for Exospheric Refilling and Natural Abundances package on the Mercury Planetary Orbiter designed to study magnetospheric dynamics. These flybys all passed from dusk to dawn through the nightside equatorial region but were noticeably different from each other. In the first flyby, we observe a low latitude boundary layer and 1 keV ions near closest approach. For flybys 2 and 3 we see ions up to 14 keV in the same location, including freshly injected precipitating ions inside the loss cone. High time resolution data from flyby 3 show variations consistent with bursty bulk flows 10s long and occurring over s periods, the first such observation in this region. MIPA data demonstrate that high‐energy injection processes are an important source of precipitation ions at Mercury.