Seasonal variations of hydrogen peroxide and water vapor on Mars: Further indications of heterogeneous chemistry

Abstract

We have completed our seasonal monitoring of hydrogen peroxide and water vapor on Mars using ground-based thermal imaging spectroscopy, by observing the planet in March 2014, when water vapor is maximum, and July 2014, when, according to photochemical models, hydrogen peroxide is expected to be maximum. Data have been obtained with the Texas Echelon Cross Echelle Spectrograph (TEXES) mounted at the 3 m–Infrared Telescope Facility (IRTF) at Maunakea Observatory. Maps of HDO and H2 O2 have been obtained using line depth ratios of weak transitions of HDO and H2 O2 divided by CO2 . The retrieved maps of H2 O2 are in good agreement with predictions including a chemical transport model, for both the March data (maximum water vapor) and the July data (maximum hydrogen peroxide). The retrieved maps of HDO are compared with simulations by Montmessin et al. (2005, J. Geophys. Res., 110, 03006) and H2 O maps are inferred assuming a mean martian D/H ratio of 5 times the terrestrial value. For regions of maximum values of H2 O and H2 O2 , we derive, for March 1 2014 (Ls = 96°), H2 O2 = 20+/−7 ppbv, HDO = 450 +/−75 ppbv (45 +/−8 pr-nm), and for July 3, 2014 (Ls = 156°), H2 O2 = 30+/−7 ppbv, HDO = 375+/−70 ppbv (22+/−3 pr-nm). In addition, the new observations are compared with LMD global climate model results and we favor simulations of H2 O2 including heterogeneous reactions on water-ice clouds.