Increased electron pressure as possible origin of magnetic field dropouts observed by RPC-MAG of comet 67P/Churyumov-Gerasimenko

The Rosetta Plasma Consortium MAGnetometer (RPC-MAG) has observed signatures of magnetic field dropouts in the inner coma region of comet 67P/Churyumov-Gerasimenko at distances from 30km to 400km, which is larger than what has been predicted by numerical simulations of the cometary plasma environment. It is still unclear how these magnetic field dropouts form in the inner coma region. In the present work, we use our newly developed multi-fluid plasma-neutral interaction model (Huang et al. 2016) to investigate this problem. The model solves the governing multi-ion MHD equations for the cometary and solar wind ions and electrons, and the Euler equations for the neutral gas fluid. We show that a strong local increase of electron pressure is capable to generate the features of the magnetic field dropouts observed by RPC-MAG: the simulation results show that a low magnetic field region is formed and the recovery phase of the magnetic field magnitude is faster than the declining phase, which suggests that the mechanism proposed here based on localized enhancement of electron pressure may provide a possible explanation for the unusually large distance of the observed magnetic field dropouts.