Modelling the Global Electric Field in the Hermean Magnetosphere with Hall MHD Simulations

With BepiColombo soon to enter its orbit around Mercury, the two electric field sensors (MEFISTO and WPT) of the PWI instrument will provide the first ever electric field measurements in the Hermean magnetosphere. Together with the particle instruments of the SERENA and MPPE suites equipped on the two spacecraft, the electric field measurements will allow a better understanding of the global plasma dynamics, and of source and loss processes at Mercury. These include global plasma convection due to the E×B drift and acceleration of charged particles by the Lorentz force.

 

So far, the global distribution of the magnetospheric electric field of Mercury is still under debate. Previous studies have adapted analytical models of the motional -v×B electric field in Earth’s magnetosphere such as the Volland-Stern potential to Mercury. However, the small length scales within the magnetospheric system and low plasma densities give rise to different effects such as the Hall effect and different types of plasma waves. The contribution of the motional electric field induced by the solar wind may play a less significant role than in Earth’s magnetosphere. Therefore, knowing the contribution of the different terms to the total electric field is necessary in order to understand the global plasma processes.

 

Modelling the electric field in Mercury’s magnetosphere can help to predict and support direct spacecraft measurements, and other simulation approaches. We apply a new Hall magnetohydrodynamic (MHD) model of Mercury’s magnetosphere based on the open-source PLUTO code [1]. We analyse the global structure of the electric field and the contribution of the different terms to the total electric field. We find that the Hall effect dominates in regions of strong currents, and that it can generally compensate the motional electric field due to opposite polarity. Furthermore, we see a strong impact of the interplanetary magnetic field with stronger electric field strengths during southward directed interplanetary magnetic field due to changing plasma properties and current systems.

 

References

[1] Mignone, A., Bodo, G., Massaglia, S., Matsakos, T., Tesileanu, O., Zanni, C., Ferrari, A.: PLUTO: A Numerical Code for Computational Astrophysics. The Astrophysical Journal Supplement Series 170(1), 228 (2007)