On the Origins of Mars' Exospheric Nonthermal Oxygen Component as Observed by MAVEN and Modeled by HELIOSARES

Abstract

The first measurements of the emission brightness of the oxygen atomic exosphere by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission have clearly shown that it is composed of a thermal component produced by the extension of the upper atmosphere and of a nonthermal component. Modeling these measurements allows us to constrain the origins of the exospheric O and, as a consequence, to estimate Mars' present oxygen escape rate. We here propose an analysis of three periods of MAVEN observations based on a set of three coupled models: a hybrid magnetospheric model (LATmos HYbrid Simulation (LatHyS)), an Exospheric General Model (EGM), and the Global Martian Circulation model of the Laboratoire de Météorologie Dynamique (LMD‐GCM), which provide a description of Mars' environment from the surface up to the solar wind. The simulated magnetosphere by LatHyS is in good agreement with MAVEN Plasma and Field Package instruments data. The LMD‐GCM modeled upper atmospheric profiles for the main neutral and ion species are compared to Neutral Gas and Ion Mass Spectrometer/MAVEN data showing that the LMD‐GCM can provide a satisfactory global view of Mars' upper atmosphere. Finally, we were able to reconstruct the expected emission brightness intensity from the oxygen exosphere using EGM. The good agreement with the averaged measured profiles by Imaging Ultraviolet Spectrograph during these three periods suggests that Mars' exospheric nonthermal component can be fully explained by the reactions of dissociative recombination of the O2+ ion in Mars' ionosphere, limiting significantly our ability to extract information from MAVEN observations of the O exosphere on other nonthermal processes, such as sputtering.

Variability of Precipitating Ion Fluxes During the September 2017 Event at Mars

“…According to Leblanc et al (), the precipitating ion flux is highly dependent on the solar zenith angle, on the position of the most intense crustal magnetic field structures, and on the orientation of the convective electric field. Indeed, Hara, Luhmann, Leblanc, Curry, Seki, et al () showed that the intensity of the precipitating ion flux peaked on the hemisphere toward which the E SW field pointed (the −E SW hemisphere).…”

On Mars's Atmospheric Sputtering After MAVEN's First Martian Year of Measurements

“…All these reactions are indeed usually considered as marginally contributing to the atmospheric escape compared to O 2 + dissociative recombination. We discussed this issue in Leblanc et al (2017) showing that at least a factor 3 difference can be retrieved by using the same cross sections. This is roughly 6 times smaller than our present estimate.…”

“…We also determine how the exosphere could be shaped by the sputtered atmospheric Leblanc et al, 2017) developed to describe Mars's exosphere at any Martian season and solar activity. We also determine how the exosphere could be shaped by the sputtered atmospheric Leblanc et al, 2017) developed to describe Mars's exosphere at any Martian season and solar activity.…”

Responses of the Martian Magnetosphere to an Interplanetary Coronal Mass Ejection: MAVEN Observations and LatHyS Results

“…A detailed description of the LatHyS model can be found in Modolo et al (, and references therein). The description of the neutral and ionospheric Martian environment that affect, among other things, the mass‐loading conditions of the SW is derived making use of the 3‐D LMD‐GCM (Chaufray et al, , ; González‐Galindo et al, ) and the 3‐D EGM (Leblanc, Chaufray, et al, ; Leblanc, Leclercq, et al, ).…”