The nature of Martian plume during solar wind interaction with Mars

Investigating the physical mechanism of ion escape on Mars is crucial for comprehending the evolution of Martian space environment. The plume structure located in the +E hemisphere of Mars plays a crucial role in the escape of planetary ions, contributing more than 20 percent to the overall ion escape rate. In this study, a three-dimensional multi-fluid Hall magnetohydrodynamics (MHD) numerical model is utilized to simulate the ion escape process of Mars. A force analysis is conducted to examine the electric field exerted on O⁺ and to investigate the density, velocity, and escape flux of O⁺. Numerical results indicate that both the convection field and the magnetic force field play essential roles in driving ion escape in the plume region and shaping the morphology of ion escaping fluxes. The plume is positioned above the magnetic pile-up boundary (MPB), as the convection field directed towards the +Z direction primarily influences the area above the MPB. Furthermore, the Hall field points outward and reaches the peak values at the MPB, while the ambipolar field peaks at the bow shock (BS). In addition, the ions escaping from the plume predominantly originates from the middle and high latitudes of the +E hemisphere on the Martian dayside. The plume escape rate and the tail escape rate are 4.33 × 10²³ s^-1 and 1.74 × 10²⁴ s^-1 respectively. The plume escape rate accounts for 24.83% of the tail escape rate and 19.89% of the overall escape rate.