CO and O2 in the Martian atmosphere with ACS NIR onboard TGO.

<p>The molecular oxygen (O2) and carbon oxide (CO) are minor constituents of the Martian atmosphere with the annual mean mixing ratio of (1560 &#177; 60 ppm) and (673 &#177; 2.6 ppm), respectively (Krasnopolsky, 2017). Both are non-condensable species and their latitudinal variations are induced by condensation and sublimation of CO₂ from the polar caps that result in enrichment and depletion and seasonal variations are following the total CO₂ amount in the atmosphere.</p><p>The Atmospheric Chemistry Suite (ACS) is a set of three spectrometers (-NIR, -MIR, and -TIRVIM) intended to observe Mars atmosphere onboard the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission (Korablev et al., 2018). The near infrared channel (NIR) is a compact spectrometer operating in the range of 0.7&#8211;1.7 &#181;m with a resolving power of &#955;/&#916;&#955; ~ 25,000. It is designed to operate in nadir and in solar occultation modes. The simultaneous vertical profiling of the O₂and CO density at altitudes of 10-60 km based on 0.76 &#181;m and 1.57 &#181;m bands, respectively, is a unique feature of the ACS NIR science in occultation. In this work we present the seasonal and latitudional distribution of the O₂ and CO mixing ratios obtained for period of 2018-2020 (MY34 and35) and the comparison with the LMD General Circulation model. We report the averaged mixing ratio for CO of ~950 ppm and for O2 of~1800 ppm at low altitudes (~20 km). Also, we detected extremely enriched CO layer at 10-15 km in the southern polar region at Ls=100-200&#176; both for MY34 and MY35.</p>