Chemistry of the dayside ionosphere of Mars

Abstract

The density calculations for nine ions CO₂⁺, N₂⁺, O₂⁺, O⁺, CO⁺, NO⁺, N⁺, H⁺ and C⁺ are made to study the chemistry of the dayside ionosphere of Mars using analytical yield spectrum approach and coupled continuity equation for the steady state condition. Among these ions; O₂⁺, NO⁺ and CO₂⁺ are major, while others are minor. The density of NO⁺ is directly related to its parent density. The ionization and dissociative ionization of CO₂ produce large amount of CO₂⁺ and O⁺, respectively, which are lost by dissociative recombination and atomic oxygen to form O₂⁺ as a dominant ion in the dayside ionosphere of Mars. The ionization and dissociative ionization of N₂ are also important processes for the production of N₂⁺ and N⁺, respectively. The ions H⁺, CO⁺ and C⁺ are entirely destroyed by CO₂. In the calculation, the loss of ions due to horizontal transport along Martian magnetic field lines is also included by solving a simplified horizontal momentum equation for ion-neutral and ion-electron collisions. It is found that the horizontal plasma transport is an important loss process for all ions above 150 km. Below this altitude, the ionosphere of Mars is controlled by a photochemical equilibrium condition. The calculated electron density is in good agreement with the measurements made by radio occultation experiment on Mariner-4 and retarding potential analyzer experiments on Viking-1 and 2.