Photochemical escape of oxygen from the Martian atmosphere: new insights from MAVEN
Abstract:One of the primary goals of the MAVEN mission is to characterize rates of atmospheric escape from Mars at the present epoch and relate those escape rates to solar drivers. One of the known escape processes is photochemical escape, where a) an exothermic chemical reaction in the atmosphere results in an upward-traveling neutral particle whose velocity exceeds planetary escape velocity and b) the particle is not prevented from escaping through any subsequent collisions.
Because escaping hot atoms are not directly measured, models of production and transport (through the atmosphere) of such atoms must be used to constrain photochemical escape rates. These models require altitude profiles of neutral densities and electron and ion densities and temperatures, as well as compositional information, all of which are measured by MAVEN instruments at the relevant altitudes (150-300 km). For every altitude profile:
- Profiles of O2+ dissociative recombination (DR) rates will be calculated from electron temperature, electron density and O2+ density.
- Profiles of energy distributions of hot O atoms will be calculated from profiles of electron and ion temperatures.
- Profiles of all neutral densities will be input into models of hot O transport in order to calculate photochemical escape fluxes from DR of O2+.
We will present photochemical escape fluxes as a function of several factors, in particular solar zenith angle and EUV flux. This, combined with further simulations with progressively higher EUV fluxes, will eventually enable a total integrated loss estimate over the course of Martian history and hence a determination of the impact of this loss process on the evolution of the Martian climate.