The BepiColombo Planetary Magnetometer MPO-MAG: What Can We Learn from the Hermean Magnetic Field?

Abstract

The magnetometer instrument MPO-MAG on-board the Mercury Planetary Orbiter (MPO) of the BepiColombo mission en-route to Mercury is introduced, with its instrument design, its calibration and scientific targets. The instrument is comprised of two tri-axial fluxgate magnetometers mounted on a 2.9 m boom and are 0.8 m apart. They monitor the magnetic field with up to 128 Hz in a $\pm 2048$ ± 2048 nT range. The MPO will be injected into an initial $480 \times 1500$ 480 × 1500 km polar orbit (2.3 h orbital period). At Mercury, we will map the planetary magnetic field and determine the dynamo generated field and constrain the secular variation. In this paper, we also discuss the effect of the instrument calibration on the ability to improve the knowledge on the internal field. Furthermore, the study of induced magnetic fields and field-aligned currents will help to constrain the interior structure in concert with other geophysical instruments. The orbit is also well-suited to study dynamical phenomena at the Hermean magnetopause and magnetospheric cusps. Together with its sister instrument Mio-MGF on-board the second satellite of the BepiColombo mission, the magnetometers at Mercury will study the reaction of the highly dynamic magnetosphere to changes in the solar wind. In the extreme case, the solar wind might even collapse the entire dayside magnetosphere. During cruise, MPO-MAG will contribute to studies of solar wind turbulence and transient phenomena.

Venus's induced magnetosphere during active solar wind conditions at BepiColombo's Venus 1 flyby

“…These small and slow CMEs are transients often seen during low solar activity phases of the solar cycle and are often called stealth CMEs because, as in this case, no clear source is identified. BepiColombo has already encountered several transient structures of this type, such as that presented in Heyner et al (2021). Although stealth CMEs typically are pushed by the solar wind, they have the capacity to interact with the planet's conductive surface and ionosphere plasma: this is especially the case for unmagnetized planets, as demonstrated in this study at Venus and also with similar events at Mars by Sánchez-Cano et al (2017) and Kajdič et al (2021).…”

“…Nevertheless, other effects more difficult to discern may also be playing a role, such as shadowing from one's own spacecraft due to attitude changes. Interestingly, Rosetta also saw a similar reduction in the GCR flux of 8 % in the vicinity of the comet 67P/Churyumov-Gerasimenko which could not be attributed to any known mechanisms (Honig et al, 2019).…”

“…We use data from the BepiColombo magnetometer MPO-MAG onboard the MPO spacecraft (Glassmeier et al, 2010;Heyner et al, 2021), at a cadence of 1 s (Fig. 2) and a lowpass filter for periods below 5 min (Fig.…”

“…Electron data from the Mercury Plasma Particle Experiment (Saito et al, 2010;Saito et al, 2021) In order to account for the solar wind activity responsible for the IMF disturbances around the Venus 1 flyby, data from the BepiColombo Radiation Monitor (BERM) are used (Pinto et al, 2021). BERM is a particle detector able to provide radiation information, in a way similar to the Standard Radiation Environment Monitor (SREM) instrument aboard several ESA missions such as Rosetta (Honig et al, 2019). In particular, it is able to measure high-energy charged particles (e.g.…”

Excess of Sodium Ions Density Required to Create a Wide Current at the Hermean Magnetopause

“…Perhaps a future BepiColombo mission will be able to answer these questions. It is assumed that the influence of the solar wind will be studied in more detail since one spacecraft of the BipiColombo mission will be in the solar wind out of the magnetosheath, while the other in the magnetosphere of Mercury [15].…”