A model of the Martian ionosphere below 70 km

The ion-neutral chemistry of the atmosphere of Mars has been studied with a one-dimensional model. Here we present the main reactions that lead to the formation of the most abundant positive and negative ions. Galactic cosmic rays ionize the atmospheric constituents, mainly CO2, and reactions of charge transfer of CO+2 with oxygen produces O+2. The further ion-neutral chemistry is quite similar to that of D-region on Earth. The relative high abundance of water and its higher proton affinity compared with other molecules, lead to the expectation that the most abundant positive ions are hydronium hydrates, H+3O(H2O)n. The chemistry includes the production of negative ions, O- and O-2, by electron capture of oxygen-bearing molecules and sinks of negative ions by electron photodetachment and ion-ion recombination. Oxygen negative ions are transformed through a chain of reactions into the carbon and nitrogen-bearing ions, CO-n and NO-n. The formation of hydrated negative ions is also considered. © 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.