A First Comparison between 3D Model Predictions of Mars’ Oxygen Corona and Early MAVEN IUVS Observations

Abstract:

Earlier observations of the Mars’ atmosphere have provided evidence that Mars was once abundance in water and CO₂, which had been depleted via various mechanisms from the surface and atmosphere throughout the history of the planet. At the current epoch, the main mechanism that induces the loss of atomic O is suggested as dissociative recombination of O₂⁺, which yields the hot O corona in the upper thermosphere and exosphere. To quantitatively understand the loss process, it is crucial to characterize the Martian hot O corona in detail by constraining the model in accordance with the analysis of the observed features of the atmosphere, allowing estimation of the global escape rate of atomic O. Here, we present a comparison between our 3D Martian hot O corona model predictions and the OI 130.4 nm emission detected by the Imaging Ultraviolet Spectrograph (IUVS) [McClintock et al., 2014] onboard Mars Atmosphere and Volatile EvolutiN (MAVEN) [Jakosky et al., 2015]. We have simulated the hot O corona by coupling our Mars application of the 3D Adaptive Mesh Particle Simulator (M-AMPS) [Tenishev et al., 2008, 2013] and the Mars Global Ionosphere-Thermosphere Model (M-GITM) [Bougher et al., 2015], based completely on our best pre-MAVEN understanding of the 3D structure of the thermosphere and ionosphere. The model predictions showed good agreement with the transition altitude from the cold thermosphere to the hot O corona, the altitude variation of the hot O density, and the spatial variation of the dayside-dominated corona. The model estimates the O escape rate of 3.46 × 10²⁵ s^-1 for the case considered. The brightness of the modeled hot O densities are a factor of a few lower than the IUVS measurement, which requires further analysis of MAVEN measurements to constrain our model as well as the possible consideration of other source mechanisms to close the gap with the observed brightness.