Volume 647, March 2021
|Number of page(s)||14|
|Section||Planets and planetary systems|
|Published online||29 March 2021|
Seasonal reappearance of HCl in the atmosphere of Mars during the Mars year 35 dusty season
Department of Physics, University of Oxford,
2 Space Research Institute (IKI), Moscow, Russia
3 Space Science Institute, Boulder, USA
4 Laboratoire de Météorologie Dynamique (LMD/CNRS), Paris, France
5 Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS/CNRS), Paris, France
Accepted: 2 February 2021
Hydrogen chloride was discovered in the atmosphere of Mars for the first time during the global dust storm in Mars year (MY) 34 (July 2018) using the Atmospheric Chemistry Suite mid-infrared channel (ACS MIR) on the ExoMars Trace Gas Orbiter. The simultaneity of variations in dust and HCl, and a correlation between water vapour and HCl, led to the proposal of a novel surface-atmosphere coupling analogous to terrestrial HCl production in the troposphere from salt aerosols. After seasonal dust activity restarted in MY 35 (August 2020), we have been monitoring HCl activity to determine whether such a coupling was validated. Here we present a new technique for analysing the absorption features of trace gases close to the ACS MIR noise level and report that HCl mixing ratios are observed to rapidly increase in both hemispheres coincidentally with the onset of the MY 35 perihelion dust season. We present the temporal evolution of the vertical distribution of HCl (0.1–6 ppbv) and of dust activity in both hemispheres. We also report two observations of >2 ppbv HCl below 10 km in the northern hemisphere during the aphelion period.
Key words: infrared: planetary systems / planets and satellites: atmospheres / planets and satellites: terrestrial planets / planets and satellites: composition / planets and satellites: detection
© ESO 2021
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