Science Advances 10 Feb 2021, https://doi.org/10.1126/sciadv.abc8843

View ORCID ProfileGeronimo L. Villanueva, View ORCID ProfileGiuliano Liuzzi, View ORCID ProfileMatteo M. J. Crismani, View ORCID ProfileShohei Aoki, View ORCID ProfileAnn Carine Vandaele, View ORCID ProfileFrank Daerden, View ORCID ProfileMichael D. Smith, Michael J. Mumma, View ORCID ProfileElise W. Knutsen, View ORCID ProfileLori Neary, View ORCID ProfileSebastien Viscardy, View ORCID ProfileIan R. Thomas, View ORCID ProfileMiguel Angel Lopez-Valverde, View ORCID ProfileBojan Ristic, View ORCID ProfileManish R. Patel, View ORCID ProfileJames A. Holmes, View ORCID ProfileGiancarlo Bellucci, View ORCID ProfileJose Juan Lopez-Moreno, and the NOMAD team

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.