Daily Variation of Heavy Carbon Dioxide in Mars Atmosphere T. A. Livengood (1,2), Th. Kostiuk (2), J. Kolasinski (2), T. Hewagama (3), W. G. Henning (1,2), M. Sornig (4), T. Stangier (5), P. Krause (5), G. Sonnabend (6) (1) CRESST, University of Maryland, USA, (2) NASA Goddard Space Flight Center, USA, (3) University of Maryland, USA, (4) Rhenish Institute for Environmental Research, Cologne, Germany, (5) University of Cologne, Germany, (6) Radiometer Physics GmbH, Meckenheim, Germany (timothy.a.livengood@nasa.gov) Abstract The atmosphere of Mars is significantly enriched in C and O heavy isotopes, detected by ground based high-resolution infrared spectroscopy as well as in situ measurements by the Phoenix lander and Mars Science Laboratory Curiosity rover. Heavy isotope enrichment is consistent with the preferential loss of light isotopes in eroding Mars’ primordial atmosphere. Infrared spectroscopy of Mars collected in May 2012 as well as in March and May of 2014 from the NASA IRTF resolves rovibrational transitions of normal-isotope carbon dioxide as well as singly-substituted minor isotopologues, enabling remote measurements of carbon and oxygen isotope ratios as a function of latitude and local time of day. Earlier measurements obtained in October 2007 demonstrated that the relative abundance of O-18 increased linearly with increasing surface temperature over a relatively warm early-afternoon temperature range, but did not extend far enough to inspect the effect of late-afternoon cooling. These results imply that isotopically enriched gas is sequestered overnight when surface temperature is minimum and desorbs through the course of the day as temperature increases. Current spectroscopic constants indicate that the peak isotopic enrichment could be significantly greater than what has been measured in situ, apparently due to sampling the atmosphere at different time of day and surface temperature. The observing runs in 2012 and 2014 measured O-18 enrichment at several local times in both morning and afternoon sectors as well as at the subsolar, equatorial, and anti-subsolar latitudes. The two runs in 2014 have additionally observed O-17 and C-13 transitions in the morning sector, from local dawn to noon. These observations include a limited sampling of measurements over Gale Crater, which can be compared with contemporary in situ measurements by the Curiosity rover to investigate the degree of agreement between in situ and remote methods and potentially to calibrate the spectroscopic constants required to accurately evaluate isotope ratios all over Mars. 18 OCO 952.8629 cm –1 CO 2 952.8808 cm –1 200 400 600 800 1000 1200 1400 Δν (MHz from LO) Radiance (erg/s/cm 2 /cm -1 /sr) 40 50 60 70 Non-LTE Figure 1: High-resolution infrared spectrum of CO 2 in Mars atmosphere at 952.8808±0.0534 cm –1 (bandwidth, not uncertainty). The measured spectrum is dominated by wings of the telluric CO 2 transition at the rest frequency, spanning the Doppler-shifted CO 2 transition formed in Mars troposphere with a non-local thermodynamic equilibrium (non-LTE) core emission formed in the mesosphere, and the 18 OCO absorption formed in the Mars troposphere. The blue curve models the emergent spectrum for standard temperature profile and surface temperature. The red curve arises from an iteratively improved lower-atmosphere temperature profile and surface temperature. Both models use the telluric isotope ratio, resulting in a poor fit to the 18 OCO feature, demonstrating the opportunity to constrain fitting the isotope ratio. EPSC Abstracts Vol. 10, EPSC2015-788-2, 2015 European Planetary Science Congress 2015 c  Author(s) 2015 E P S C European Planetary Science Congress