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

¹ LESIA, Observatoire de Paris, CNRS, UPMC, Univ. Paris Diderot 92195 Meudon France
e-mail: therese.encrenaz@obspm.fr
² SwRI, Div. 15, San Antonio, TX 78228, USA
³ LATMOS, IPSL, 75252 Paris Cedex 05, France
⁴ LMD, IPSL, 75252 Paris Cedex 05, France
⁵ Dept. of Physics, University of California Davis, CA 95616, USA
⁶ Dept. of Astronomy, University of Texas at Austin, TX 78712-1083, USA
⁷ Dept. of Atmospheric, Oceanic & Space Sciences, University of Michigan, Ann Arbor, MI 48109-2143, USA

Received: 2 December 2014
Accepted: 11 April 2015

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 H₂O₂ have been obtained using line depth ratios of weak transitions of HDO and H₂O₂ divided by CO₂. The retrieved maps of H₂O₂ 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 H₂O maps are inferred assuming a mean martian D/H ratio of 5 times the terrestrial value. For regions of maximum values of H₂O and H₂O₂, we derive, for March 1 2014 (Ls = 96°), H₂O₂ = 20+/−7 ppbv, HDO = 450 +/−75 ppbv (45 +/−8 pr-nm), and for July 3, 2014 (Ls = 156°), H₂O₂ = 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 H₂O₂ including heterogeneous reactions on water-ice clouds.