Isotopic composition of CO<sub>2</sub> in the atmosphere of Mars: fractionation by diffusive separation observed by the ExoMars Trace Gas Orbiter - Archive ouverte HAL Access content directly
Journal Articles Journal of Geophysical Research. Planets Year : 2021

Isotopic composition of CO2 in the atmosphere of Mars: fractionation by diffusive separation observed by the ExoMars Trace Gas Orbiter

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Franck Montmessin
Franck Lefèvre
Ashwin Braude
  • Function : Author
Lucio Baggio

Abstract

Isotopic ratios in atmospheric CO2 are shaped by various processes throughout Mars' history, and can help understand what the atmosphere of early Mars was like to sustain liquid water on its surface. In this study, we monitor the O and C isotopic composition of CO2 between 70 and 130 km for more than half a Martian year using solar occultation observations by the Atmospheric Chemistry Suite onboard the ExoMars Trace Gas Orbiter. We find the vertical trends of the isotopic ratios to be consistent with the expectations from diffusive separation above the homopause, with average values below this altitude being consistent with Earth-like fractionation (δ13C =-3 ± 37 ; δ18O =-29 ± 38 ; δ17O =-11 ± 41). Using these measurements, we estimate that at least 20-40% of primordial C on Mars has escaped to space throughout history. The total amount of C lost from the atmosphere is likely to be well in excess of this lower limit, due to carbonate formation and further sink processes. In addition, we propose a photochemical transfer of light O from H2O to CO2 to explain the larger enrichment in the 18O/16O ratio in H2O than in CO2.
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Dates and versions

insu-03473299 , version 1 (09-12-2021)
insu-03473299 , version 2 (19-12-2021)

Licence

Attribution - CC BY 4.0

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Juan Alday, Colin F. Wilson, Patrick G. J. Irwin, Alexander Trokhimovskiy, Franck Montmessin, et al.. Isotopic composition of CO2 in the atmosphere of Mars: fractionation by diffusive separation observed by the ExoMars Trace Gas Orbiter. Journal of Geophysical Research. Planets, 2021, 127 (12), pp.e2021JE006992. ⟨10.1029/2021je006992⟩. ⟨insu-03473299v2⟩
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