Water heavily fractionated as it ascends on Mars as revealed by ExoMars/NOMAD

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Isotopic ratios and, in particular, the water D/H ratio are powerful tracers of the evolution and transport of water on Mars. From measurements performed with ExoMars/NOMAD, we observe marked and rapid variability of the D/H along altitude on Mars and across the whole planet. The observations (from April 2018 to April 2019) sample a broad range of events on Mars, including a global dust storm, the evolution of water released from the southern polar cap during southern summer, the equinox phases, and a short but intense regional dust storm. In three instances, we observe water at very high altitudes (>80 km), the prime region where water is photodissociated and starts its escape to space. Rayleigh distillation appears the be the driving force affecting the D/H in many cases, yet in some instances, the exchange of water reservoirs with distinctive D/H could be responsible. © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science.
This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401 and 4000121493), by the Spanish MICINN through its Plan Nacional, by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), and by the Spanish Science Ministry Centro de Excelencia Severo Ochoa Program under grant SEV-2017-0709, as well as by the U.K. Space Agency through grants ST/R005761/1, ST/P001262/1, ST/R001405/1, and ST/S00145X/1 and the Italian Space Agency through grant 2018-2-HH.0. This work was supported by NASA’s Mars Program Office under WBS 604796, “Participation in the TGO/NOMAD investigation of trace gases on Mars” and by NASA’s SEEC initiative under grant number NNX17AH81A, “Remote sensing of planetary atmospheres in the solar system and beyond.” M.J.C. was supported by the NASA Postdoctoral Program at the NASA Goddard Space Flight Center, administered by Universities Space Research Association (USRA) under contract with NASA. S.A. is postdoctoral researcher of the Belgian Fund for Scientific Research (FNRS).