Forbidden atomic oxygen emissions in the Martian dayside upper atmosphere

TL;DR

This study models the photochemistry of forbidden atomic oxygen emissions in the Martian dayside upper atmosphere, comparing results with NOMAD-TGO observations and suggesting conditions for their simultaneous detection.

Contribution

Developed a photochemical model that explains forbidden atomic oxygen emissions and aligns with recent NOMAD-TGO measurements, enhancing understanding of Martian upper atmospheric chemistry.

Findings

Model matches NOMAD-TGO observations when reducing neutral densities by half.

Forbidden emissions are observable under near perihelion and solar maximum conditions.

Model suggests all forbidden emissions can be detected in the dayside spectra.

Abstract

Recently, Nadir and Occultation for Mars Discovery (NOMAD) ultraviolet and visible spectrometer instrument on board the European Space Agency's ExoMars Trace Gas Orbiter (TGO) simultaneously measured the limb emission intensities for both [OI] 2972 and 5577 {\AA} (green) emissions in the dayside of Martian upper atmosphere. We aim to explore the photochemistry of all these forbidden atomic oxygen emissions ([OI] 2972, 5577, 6300, 6464 {\AA}) in the Martian daylight upper atmosphere and suitable conditions for the simultaneous detection of these emissions lines in the dayside visible spectra. A photochemical model is developed to study the production and loss processes of O(1S) and O(1D) by incorporating various chemical reactions of different O-bearing species in the upper atmosphere of Mars. By reducing Fox (2004) modelled neutral density profiles by a factor of 2, the calculated limb intensity profiles for [OI] 5577 and 2972 {\AA} emissions are found to be consistent with the NOMAD-TGO observations. In this case, at altitudes below 120 km, our modelled limb intensity for [OI] 6300 {\AA} emission is smaller by a factor 2 to 5 compared to that of NOMAD-TGO observation for [OI] 2972 {\AA} emission, and above this distance it is comparable with the upper limit of the observation. We studied various parameters which can influence the limb intensities of these atomic oxygen forbidden emission lines. Our calculated limb intensity for [OI] 6300 {\AA} emission, when the Mars is at near perihelion and for solar maximum condition, suggests that all these forbidden emissions should be observable in the NOMAD-TGO visible spectra taken on the dayside of Martian upper atmosphere. More simultaneous observations of forbidden atomic oxygen emission lines will help to understand the photochemical processes of oxygen-bearing species in the dayside Martian upper atmosphere.