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 (600 K – 2300 K) 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 ∞ = 2300 K, the escape flux does not increase and has the maximum flux ∼4.3 × 10 6 cm −2 s −1 and escape rate ∼3.5 × 10 24 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.