Present-day water loss from Mars provides insight into Mars’s past habitability1,2,3. Its main mechanism is thought to be Jeans escape of a steady hydrogen reservoir sourced from odd-oxygen reactions with near-surface water vapour2, 4,5. The observed escape rate, however, is strongly variable and correlates poorly with solar extreme-ultraviolet radiation flux6,7,8, which was predicted to modulate escape9. This variability has recently been attributed to hydrogen sourced from photolysed middle atmospheric water vapour10, whose vertical and seasonal distribution is only partly characterized and understood11,12,13. Here, we report multi-annual observational estimates of water content and dust and water transport to the middle atmosphere from Mars Climate Sounder data. We provide strong evidence that the transport of water vapour and ice to the middle atmosphere by deep convection in Martian dust storms can enhance hydrogen escape. Planet-encircling dust storms can raise the effective hygropause (where water content rapidly decreases to effectively zero) from 50 to 80 km above the areoid (the reference equipotential surface). Smaller dust storms contribute to an annual mode in water content at 4050 km that may explain seasonal variability in escape. Our results imply that Martian atmospheric chemistry and evolution can be strongly affected by the meteorology of the lower and middle atmosphere of Mars.

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This work was supported by NASA’s Mars Data Analysis and Nexus for Exoplanet System Science programmes (NNX14AM32G and NNX15AE05G to N.G.H. and NNN13D465T to A.K.). Work at the Jet Propulsion Laboratory, California Institute of Technology is performed under contract with NASA. The authors thank A. D. Toigo for providing CRISM data.

Author information


  1. Department of Atmospheric and Planetary Sciences, Hampton University, Hampton, VA, USA

    • Nicholas G. Heavens
  2. National Aeronautics and Space Administration Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    • Armin Kleinböhl
    • , David M. Kass
    • , Paul O. Hayne
    • , Sylvain Piqueux
    • , James H. Shirley
    •  & John T. Schofield
  3. Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, CO, USA

    • Michael S. Chaffin
  4. Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA

    • Jasper S. Halekas
  5. Synoptic Science, Altadena, CA, USA

    • Daniel J. McCleese


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N.G.H. and A.K. conceived and designed the study with input from M.S.C. N.G.H. designed and analysed the dust and water vapour flux diagnoses and analysed the inferred water vapour information. A.K. designed the inferred water vapour diagnosis. J.S.H. processed and interpreted hydrogen corona observations from MAVEN. All authors assisted N.G.H. with the preparation of the manuscript.

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The authors declare no competing financial interests.

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Correspondence to Nicholas G. Heavens.

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