Hot carbon corona in Mars’ upper thermosphere and exosphere: 1. Mechanisms and structure of the hot corona for low solar activity at equinox

Abstract

Two important source reactions for hot atomic carbon on Mars are photodissociation of CO and dissociative recombination of CO+; both reactions are highly sensitive to solar activity and occur mostly deep in the dayside thermosphere. The production of energetic particles results in the formation of hot coronae that are made up of neutral atoms including hot carbon. Some of these atoms are on ballistic trajectories and return to the thermosphere, and others escape. Understanding the physics in this region requires modeling that captures the complicated dynamics of hot atoms in 3-D. This study evaluates the carbon atom inventory by investigating the production and distribution of energetic carbon atoms using the full 3-D atmospheric input. The methodology and details of the hot atomic carbon model calculation are given, and the calculated total global escape of hot carbon from the assumed dominant photochemical processes at a fixed condition, equinox (Ls = 180°), and low solar activity (F10.7 = 70 at Earth) are presented. To investigate the dynamics of these energetic neutral atoms, we have coupled a self-consistent 3-D global kinetic model, the Adaptive Mesh Particle Simulator, with a 3-D thermosphere/ionosphere model, the Mars Thermosphere General Circulation Model to provide a self-consistent global description of the hot carbon corona in the upper thermosphere and exosphere. The spatial distributions of density and temperature and atmospheric loss are simulated for the case considered.