A Map of D/H on Mars using EXES Aboard SOFIA

(Rescheduled from March 30) Integrated over the planetary disk, the measurement of the D/H ratio on Mars is an important indicator of the loss of water over the history of the planet, through the process of differential escape. At a local scale, it is also a diagnostic of the water exchange with surface regolith, through fractionation due to differential condensation processes. A global measurement of D/H on Mars was first achieved by Owen et al. (1988), indicating an enrichment by a factor 6 (+/- 3) wrt the terrestrial value (VSMOW). We have used EXES aboard SOFIA to obtain a map of D/H on Mars by measuring simultaneously weak transitions of HDO and H2O in the high-resolution mode in the 8-micron range. Observations were made on April 8, 2014, near northern summer solstice and near opposition (Mars diameter = 15 arcsec). We have inferred an averaged D/H value of 4.4 (+1.0, -0.6) times the VSMOW, with a moderate enrichment from south to north (from 4 to 5 times the VSMOW). Our results in agreement with theoretical models based on the Vapor Pressure Isotopic Effect process. They are in global agreement with Villanueva et al. (2015) and Krasnopolsky (2015), but imply less early water content than inferred by Villanueva et al. (2015). Our study has been published in A&A, 586, A62 (2016).