No detection of SO2, H2S, or OCS in the atmosphere of Mars from the first two Martian years of observations from TGO/ACS

TL;DR

This study analyzed Martian atmospheric data from the TGO/ACS instrument over two years and found no detectable levels of sulfur gases, setting new upper limits and suggesting minimal volcanic outgassing.

Contribution

First comprehensive upper limit analysis of SO2, H2S, and OCS in Mars atmosphere using TGO/ACS data, improving constraints on volcanic activity.

Findings

No detection of SO2, H2S, or OCS above 3-sigma confidence.

Established new lower upper limits for these sulfur species.

Passive volcanic outgassing of SO2 is below 2 ktons/day.

Abstract

The detection of sulphur species in the Martian atmosphere would be a strong indicator of volcanic outgassing from the surface of Mars. 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. 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. For the most optimal sensitivity conditions, we determine 1-sigma 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 3-sigma confidence threshold. We therefore infer that passive volcanic outgassing of SO2 must be below 2 ktons/day.