Test particle comparison of heavy atomic and molecular ion distributions at Mars

Abstract

This study uses the Mars Test Particle simulation to create virtual detections of O+, O2+, and CO2+ in an orbital configuration in the Mars space environment. These atomic and molecular planetary pickup ions are formed when the solar wind directly interacts with the neutral atmosphere, causing the ions to be accelerated by the background convective electric field. The subsequent ion escape is the subject of great interest, specifically with respect to which species dominates ion loss from Mars. O+ is found to be the dominant escaping ion because of the large sources of transported ions in the low-energy (<10 eV) and high-energy (>1 keV) range. O2+ and CO2+ are observed at these energy ranges but with much lower fluxes and are generally only found in the tail between 10 eV and 1 keV. Using individual particle traces, we reveal the origin and trajectories of the low-energy downtail O + populations and high-energy polar O+ populations that contribute to the total escape. Comparing them against O2+ and CO2+ reveals that the extended hot oxygen corona contributes to source regions of high- and low-energy escaping ions. Additionally, we present results for solar minimum and maximum conditions with respect to ion fluxes and energies in order to robustly describe the physical processes controlling planetary ion distributions and atmospheric escape. Key Points O+ is dominant heavy species escaping Mars High altitude O+ drives high and low energy distributions not seen in heavies High and low energy O+ may not be detected and heavies/O can be overestimated ©2014. American Geophysical Union. All Rights Reserved.