Forces, Electric Fields and Currents at the Martian MPB: MAVEN Observations and Multifluid MHD Simulation Results.

The Martian MPB (Magnetic Pileup Boundary) is a key boundary in the Mars/Solar Wind interaction as it is in this location that the momentum and energy from the solar wind plasma are transferred to the planetary plasma. Since this interaction is collisionless, the transfer is mediated by electric and magnetic fields. In a previous work (Boscoboinik et al., 2020), we used the minimum variance analysis of the magnetic field (MVAB) to derive the boundarys normal vector, its thickness and the associated current density for a crossing on March 16th, 2016. We observe that the MPB thickness is of the order of the magnetosheath solar wind proton inertial length, which is consistent with their demagnetization due to the Hall electric field. In the present work we combine MAVEN data and multifluid MHD (Dong et al., 2014) simulation results to study the electric fields, currents and forces acting on the MPB at sub-ion scales for the same orbit. The simulation results are analysed and compared with MAVEN/MAG, SWIA, LPW and STATIC data for validation. In particular, we find that the current densities obtained from MAVEN data are consistent with the values obtained in the simulation. Also, the Hall electric force points sunward in both cases. Finally, we use the simulation results to compare the electric field terms within the generalized Ohms Law. We find that in the subsolar region the Hall electric field dominates over the solar wind convective electric field and electron pressure gradient. In summary, this electric field term is responsible for stopping the solar wind protons at the MPB while accelerating the solar wind electrons into the magnetic pileup region, carrying the magnetic field lines frozen into them.