O⁺ Escape in the polar ion exosphere of Mars

Abstract

A model for the polar ion exosphere of Mars is developed to calculate the escape fluxes of oxygen ions and electrons through the plasmasheet of Mars at different exospheric temperatures (600K - 2300K) along the magnetic field lines originating from the baropause at latitude 75 degrees and longitude zero degrees. The intensity of the magnetic field lines in the noon-midnight meridian plane at all latitudes are calculated by assuming that Mars has a weak magnetic field of dipolar nature. To calculate the electric potential in the region of magnetic field, the quasi-neutrality condition is satisfied in such a way that escape fluxes of oxygen ions and electrons have to be equal at every point. It has been found that above T_∞ = 2300K, the escape flux does not increase and has the maximum flux ~4.3 × 10⁶cm^-2s^-1 and escape rate ~3.5 × 10²⁴ ions s^-1. These values show close agreement with the observations taken by the TAUS and ASPERA experiments in the plasmasheet of Mars. The present calculation concludes that O⁺ ions in the plasmasheet of Mars are mainly due to the escape of oxygen ions from the ionosphere in presence of a charge separation electric field.