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

¹ Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Paris, France
e-mail: ashwin.braude@latmos.ipsl.fr
² AOPP, Oxford University, Oxford, UK
³ Space Research Institute (IKI) RAS, Moscow, Russia
⁴ Laboratoire de Météorologie Dynamique/IPSL, Sorbonne Université, ENS, PSL Research University, Ecole Polytechnique, CNRS, Paris, France

Received: 7 October 2021
Accepted: 8 November 2021

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.