Water is a requirement for life as we know it1. Indirect evidence of transient liquid water has been observed from orbiter on equatorial Mars2, in contrast with expectations from large-scale climate models. The presence of perchlorate salts, which have been detected at Gale crater on equatorial Mars by the Curiosity rover3,4, lowers the freezing temperature of water5. Moreover, perchlorates can form stable hydrated compounds and liquid solutions by absorbing atmospheric water vapour through deliquescence6,7. Here we analyse relative humidity, air temperature and ground temperature data from the Curiosity rover at Gale crater and find that the observations support the formation of night-time transient liquid brines in the uppermost 5 cm of the subsurface that then evaporate after sunrise. We also find that changes in the hydration state of salts within the uppermost 15 cm of the subsurface, as measured by Curiosity, are consistent with an active exchange of water at the atmosphere–soil interface. However, the water activity and temperature are probably too low to support terrestrial organisms8. Perchlorates are widespread on the surface of Mars9 and we expect that liquid brines are abundant beyond equatorial regions where atmospheric humidity is higher and temperatures are lower.

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We are grateful to all of the scientists and engineers who spent many years working to make the MSL mission such a success. We also acknowledge the contribution of the COSPAR Special Region Panel, and J-F. Buenestado-Castro for his support in the documentation process. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

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  1. Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), 18100 Armilla, Granada, Spain

    • F. Javier Martín-Torres
    •  & Patricia Valentín-Serrano
  2. Division of Space Technology, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, S98192 Kiruna, Sweden

    • F. Javier Martín-Torres
  3. Centro de Astrobiología (INTA-CSIC), 28850 Torrejón de Ardoz, Madrid, Spain

    • María-Paz Zorzano
    •  & Patricia Valentín-Serrano
  4. Earth Observation Research, Finnish Meteorological Institute, 00101 Helsinki, Finland

    • Ari-Matti Harri
    • , Maria Genzer
    •  & Osku Kemppinen
  5. Arecibo Observatory, Universities Space Research Association, Arecibo, Puerto Rico 00612, USA

    • Edgard G. Rivera-Valentin
  6. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA

    • Insoo Jun
    • , Michael Mischna
    •  & Ashwin R. Vasavada
  7. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

    • James Wray
  8. Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen, Denmark

    • Morten Bo Madsen
  9. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany

    • Walter Goetz
  10. Lunar and Planetary Lab, University of Arizona, Tucson, Arizona 210063, USA

    • Alfred S. McEwen
  11. Arizona State University, Tempe, Arizona 85281, USA

    • Craig Hardgrove
  12. College of Engineering University of Michigan, Ann Arbor, Michigan 48109, USA

    • Nilton Renno
  13. Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, Arkansas 72701, USA

    • Vincent F. Chevrier
  14. Laboratorio de Química de Plasmas y Estudios Planetarios, Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico D.F. 04510, México

    • Rafael Navarro-González
  15. Instituto de Geociencias (CSIC-UCM), 28040 Madrid, Spain

    • Jesús Martínez-Frías
  16. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

    • Pamela Conrad
  17. Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA

    • Tim McConnochie
  18. UK Centre for Astrobiology, School of Physics and Astronomy, Edinburgh EH9 3JZ, UK

    • Charles Cockell
  19. IRAP, Université Toulouse, CNRS, 14 avenue Edouard Belin, 31400 Toulouse, France

    • Gilles Berger
  20. Department of Earth and Planetary Sciences, University of California, Davis, California 95616, USA

    • Dawn Sumner
  21. Planetary Science Institute, Tucson, Arizona 85719, USA

    • David Vaniman


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F.J.M-T. and M-P.Z. designed the study, prepared the figures, and led the writing of the paper with contributions from the rest of the authors. P.V-S. processed REMS data. A-M.H., M.G. and O.K. processed RHS/REMS data. E.G.R-V. and V.F.C. provided subsurface model simulations. I.J. and C.H. processed DAN data. A.S.M. provided RSL images. All the authors contributed to the analysis discussion, and to the writing process.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to F. Javier Martín-Torres.

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