Forbidden Atomic Oxygen Emissions In The Martian Dayside Upper Atmosphere


Neutral density distribution in the Martian upper atmosphere. The density profiles of major species are taken from Fox (2004) for solar minimum condition. Green and yellow shaded areas represent the variability in the NGIMS measured CO2 and O densities during September 2019 for solar zenith angle less than 40◦

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 Å (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 Å) 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 Å 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 Å emission is smaller by a factor 2 to 5 compared to that of NOMAD-TGO observation for [OI] 2972 Å 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 Å 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.

Susarla Raghuram, Sonal Kumar Jain, Anil Bhardwaj

Comments: 12 pages, 5 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (physics.ao-ph)
Cite as: arXiv:2012.05593 [astro-ph.EP] (or arXiv:2012.05593v1 [astro-ph.EP] for this version)
Submission history
From: Susarla Raghuram
[v1] Thu, 10 Dec 2020 11:28:35 UTC (144 KB)
https://arxiv.org/abs/2012.05593
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