Research ArticleASTRONOMY

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

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Science Advances  10 Feb 2021:
Vol. 7, no. 7, eabc8843
DOI: 10.1126/sciadv.abc8843
  • Fig. 1 Representative spectra of the main NOMAD orders used to sample HDO (left) and H2O (right) taken on June 2018 for a SO altitude of 26 km.

    The observations were taken during the GDS and show that the two bands (ν1 of HDO and 2ν2 of H2O) have similar opacities and, therefore, comparable curves of growth and altitude sensitivity.

  • Fig. 2 Seasonal variability of water (left) and the D/H (right) for the northern hemisphere (top) and the southern hemisphere (bottom).

    Only H2O values with sigmas lower than 15 parts per million by volume (ppmv) and D/H values with sigmas lower than 0.8 VSMOW are shown (point-by-point error bars are presented in fig. S7). Because of the ExoMars/TGO orbit, there is an intrinsic relationship between the seasonal and latitudinal sampling for the occultations, and the latitude subpanels indicate which latitudes are sampled during a particular instance. Water is observed to reach the upper regions of the atmosphere (>80 km) during indicated events: (i) during the GDS, (ii) during the regional dust storm, and (ii) during southern summer, in which we observe a localized upper atmosphere water excess.

  • Fig. 3 Latitudinal variability of water and D/H across the seasons, sampling two equinoxes, a solstice, a global and a regional dust storm, and the injection of water into the atmosphere from the southern polar cap during southern summer.

    Only H2O values with sigmas lower than 15 ppmv and D/H values with sigmas lower than 1.5 VSMOW are shown. The panels clearly show the evolution of the water cycle across these complex events, revealing marked changes in the water and D/H distributions across the events. The sparsity of valid D/H datasets considering this fine temporal sampling does not allow us to fully capture every detail of the latitude by altitude variability, yet two points are clearly observed: (i) The water released from the southern polar cap has a distinctive 6- to 7-VSMOW enrichment in D/H, and (ii) during southern fall (Ls 300 to 320 and Ls 330 to 360), the hygropause is compacted in the southern hemisphere, leading also to very low D/H at these latitudes and season.

Supplementary Materials

  • Supplementary Materials

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

    Geronimo L. Villanueva, Giuliano Liuzzi, Matteo M. J. Crismani, Shohei Aoki, Ann Carine Vandaele, Frank Daerden, Michael D. Smith, Michael J. Mumma, Elise W. Knutsen, Lori Neary, Sebastien Viscardy, Ian R. Thomas, Miguel Angel Lopez-Valverde, Bojan Ristic, Manish R. Patel, James A. Holmes, Giancarlo Bellucci, Jose Juan Lopez-Moreno, NOMAD team

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    • Sections S1 and S2
    • Figs. S1 to S7
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