Model investigation of the influence of the crustal magnetic field on the oxygen ion distribution in the near Martian tail

To investigate the influence of the Martian crustal magnetic field on the acceleration and escape of the planetary ions in the near tail region, the distributions of planetary oxygen ions are studied by means of test particle simulation in an electromagnetic environment created by a recent multispecies Magnetohydrodynamics (MHD) simulation of the solar wind interaction with Mars, with crustal field included or excluded. Results under different crustal field conditions are compared to determine the effects of crustal field. It is found that when crustal field is present, draped magnetic field lines are replaced by closed field lines in the near tail region and the electric field is also intensified because of the Hall effect. As a result, the oxygen ion distribution reveals distinct stream structures in the tail region when crustal field is included, with one hot streamat the central tail and two cold streams at the flank of the tail. Some energetic ions inside the hot stream are accelerated toward the planet, instead of escaping downstream.