Herschel/HIFI observations of Mars: first detection of O_2 at submillimetre wavelengths and upper limits on HCl and H_2O_2

TL;DR

This study reports the first detection of molecular oxygen at submillimetre wavelengths in Mars' atmosphere using Herschel/HIFI, providing new measurements and upper limits for HCl and H_2O_2.

Contribution

It presents the first detection of O_2 at submillimetre wavelengths in Mars' atmosphere and offers new constraints on HCl and H_2O_2 levels.

Findings

O_2 volume mixing ratio of 1400 +/- 120 ppm

Upper limits of 200 ppt for HCl and 2 ppb for H_2O_2

Vertical profile of O_2 may not be constant

Abstract

We report on an initial analysis of Herschel/HIFI observations of hydrogen chloride (HCl), hydrogen peroxide (H_2O_2), and molecular oxygen (O_2) in the Martian atmosphere performed on 13 and 16 April 2010 (L_s ~ 77{\deg}). We derived a constant volume mixing ratio of 1400 +/- 120 ppm for O_2 and determined upper limits of 200 ppt for HCl and 2 ppb for H_2O_2. Radiative transfer model calculations indicate that the vertical profile of O_2 may not be constant. Photochemical models determine the lowest values of H_2O_2 to be around L_s ~ 75{\deg} but overestimate the volume mixing ratio compared to our measurements.