Water heavily fractionated as it ascends on Mars as revealed by ExoMars/NOMAD
Gerónimo Villanueva, Giuliano Liuzzi, Matteo Crismani, Shohei Aoki, Ann Carine Vandaele, Frank Daerden, M. D. Smith, M. J. Mumma, Elise Wright Knutsen, Lori Neary, S. Viscardy, Ian Thomas, M. Á. López‐Valverde, Bojan Ristic, Manish Patel, James Holmes, G. Bellucci, J. J. López‐Moreno, NOMAD team
Abstract
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.