<i>Herschel</i>/HIFI observations of Mars: First detection of O₂at submillimetre wavelengths and upper limits on HCl and H₂O₂

We report on an initial analysis of <i>Herschel<i/>/HIFI observations of hydrogen chloride (HCl), hydrogen peroxide (H<sub>2<sub/>O<sub>2<sub/>), and molecular oxygen (O<sub>2<sub/>) in the Martian atmosphere performed on 13 and 16 April 2010 (<i>L<i/><sub>s<sub/> ~ 77°). We derived a constant volume mixing ratio of 1400 <i>±<i/> 120 ppm for O<sub>2<sub/> and determined upper limits of 200 ppt for HCl and 2 ppb for H<sub>2<sub/>O<sub>2<sub/>. Radiative transfer model calculations indicate that the vertical profile of O<sub>2<sub/> may not be constant. Photochemical models determine the lowest values of H<sub>2<sub/>O<sub>2<sub/> to be around <i>L<i/><sub>s<sub/> ~ 75° but overestimate the volume mixing ratio compared to our measurements.