First Observation of the Oxygen 630 nm Emission in the Martian Dayglow. Issue 8 (21st April 2021)

• Record Type: Journal Article
• Authors: Gérard, J.‐C.; Aoki, S.; Gkouvelis, L.; Soret, L.; Willame, Y.; Thomas, I. R.; Depiesse, C.; Ristic, B.; Vandaele, A. C.; Hubert, B.; Daerden, F.; Patel, M. R.; López‐Moreno, J.‐J.; Bellucci, G.; Mason, J. P.; López‐Valverde, M. A.
• Is Part Of: Geophysical research letters. Volume 48:Issue 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-04-21
• Subjects: composition, EXOMARS -- dayglow -- Mars -- oxygen -- visible; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL092334
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Following the recent detection of the oxygen green line airglow on Mars, we have improved the statistical analysis of the data recorded by the NOMAD/UVIS instrument on board the ExoMars Trace Gas Orbiter mission by summing up hundreds of spectra to increase the signal‐to‐noise ratio. This led to the observation of the OI 630 nm emission, the first detection in a planetary atmosphere outside the Earth. The average limb profile shows a broad peak intensity of 4.8 kR near 150 km. Comparison with a photochemical model indicates that it is well predicted by current photochemistry, considering the sources of uncertainty. The red/green line intensity ratio decreases dramatically with altitude as a consequence of the efficient quenching of O( 1 D) by CO2 . Simultaneous observations of the green and red dayglow will provide information on variations in the thermosphere in response to seasonal changes and the effects of solar events. Plain Language Summary: The green and red oxygen emissions at 557.7 and 630 nm, respectively, are among the dominant spectral features of the terrestrial dayglow and aurora. Recently, the presence of the green emission was also observed in the Martian dayglow using the NOMAD/UVIS instrument on board the ExoMars Trace Gas Orbiter mission. The red line was expected to be significantly weaker as the long‐lived upper state of the transition is deactivated by collisions with ambient CO2 . Further statistical treatment of the spectra collected during 1.5 years near solar minimum has lead to the discovery of the presence of the 630 nm dayglow emission. The averaged limb profile shows a maximum limb brightness near 150 km about 30 times weaker than the green line. The altitude and brightness of the red emission are in agreement with those simulated with a photochemical model for the same conditions as the observations. The same model also matches the characteristics of the averaged 557.7‐nm dayglow profile observed simultaneously. Variations in the characteristics of the oxygen emissions are related to changes in the composition of the Martian upper atmosphere such as those generated by seasons and energetic solar events. Key Points: The oxygen 630‐nm emission has been detected in the Mars dayglow with the UVIS‐NOMAD/UVIS instrument on board EXOMARS Trace Gas Orbiter The 630‐nm emission is broadly distributed in the thermosphere with a maximum intensity at the limb of ∼4 kiloRayleighs near 150 km Photochemical model simulations predict O(1D) and O(1S) densities in agreement with the observed limb profiles