No detection of SO2, H2S, or OCS in the atmosphere of Mars from the first two Martian years of observations from TGO/ACS
Forget, F.; Montmessin, F.; Fedorova, A. A.; Olsen, K. S.; Millour, E.; Trokhimovskiy, A.; Lefèvre, F.; Patrakeev, A.; Wilson, C. F.; Baggio, L.; Alday, J.; Shakun, A.; Korablev, O. I.; Braude, A. S.; Lacombe, G.; Irbah, A.
France, United Kingdom, Russia
Abstract
Context. The detection of sulphur species in the Martian atmosphere would be a strong indicator of volcanic outgassing from the surface of Mars.
Aims: We wish to establish the presence of SO2, H2S, or OCS in the Martian atmosphere or determine upper limits on their concentration in the absence of a detection.
Methods: We perform a comprehensive analysis of solar occultation data from the mid-infrared channel of the Atmospheric Chemistry Suite instrument, on board the ExoMars Trace Gas Orbiter, obtained during Martian years 34 and 35.
Results: For the most optimal sensitivity conditions, we determine 1σ upper limits of SO2 at 20 ppbv, H2S at 15 ppbv, and OCS at 0.4 ppbv; the last value is lower than any previous upper limits imposed on OCS in the literature. We find no evidence of any of these species above a 3σ confidence threshold. We therefore infer that passive volcanic outgassing of SO2 must be below 2 ktons day−1.