A possible mechanism for the formation of magnetic field dropouts in the coma of 67P/Churyumov-Gerasimenko

Abstract

The Rosetta Plasma Consortium MAGnetometer (RPC-MAG) has detected signatures of diamagnetic regions associated with comet 67P/Churyumov-Gerasimenko at distances from 30 to 400 km at different heliocentric distances, which is larger than what has been predicted by numerical simulations of the cometary plasam environment. The physical mechanism behind these diamagnetic regions is still unknown. In this work, we use our newly developed multifluid plasma-neutral model to explore a possible physical mechanism that might create such regions. The model solves the governing multifluid magnetohydrodynamic equations for cometary and solar wind ions and electrons, and the Euler equations for the neutral gas fluid. We find that a local increase of electron thermal pressure is capable of generating many of the observed features of the diamagnetic regions observed by RPC-MAG. The simulation results show that a magnetic field-free region is formed and the recovery phase of the magnetic field magnitude is faster than the declining phase.