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Surface clay formation during short-term warmer and wetter conditions on a largely cold ancient Mars

Nature Astronomyvolume 2pages206213 (2018) | Download Citation

Abstract

The ancient rock record for Mars has long been at odds with climate modelling. The presence of valley networks, dendritic channels and deltas on ancient terrains points towards running water and fluvial erosion on early Mars1, but climate modelling indicates that long-term warm conditions were not sustainable2. Widespread phyllosilicates and other aqueous minerals on the Martian surface3,4,5,6 provide additional evidence that an early wet Martian climate resulted in surface weathering. Some of these phyllosilicates formed in subsurface crustal environments5, with no association with the Martian climate, while other phyllosilicate-rich outcrops exhibit layered morphologies and broad stratigraphies7 consistent with surface formation. Here, we develop a new geochemical model for early Mars to explain the formation of these clay-bearing rocks in warm and wet surface locations. We propose that sporadic, short-term warm and wet environments during a generally cold early Mars enabled phyllosilicate formation without requiring long-term warm and wet conditions. We conclude that Mg-rich clay-bearing rocks with lateral variations in mixed Fe/Mg smectite, chlorite, talc, serpentine and zeolite occurrences formed in subsurface hydrothermal environments, whereas dioctahedral (Al/Fe3+-rich) smectite and widespread vertical horizonation of Fe/Mg smectites, clay assemblages and sulphates formed in variable aqueous environments on the surface of Mars. Our model for aluminosilicate formation on Mars is consistent with the observed geological features, diversity of aqueous mineralogies in ancient surface rocks and state-of-the-art palaeoclimate scenarios.

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Acknowledgements

The authors are grateful for support from the National Aeronautics and Space Administration Astrobiology Institute (grant NNX15BB01 to J.L.B.) and Mars Data Analysis Program (grant NNX12AJ33G to J.L.B.), as well as the project ‘icyMARS’, European Research Council Starting Grant 307496 (to A.G.F.), a Smithsonian Senior Fellowship (to M.A.V.) and Deutsches Zentrum für Luft- und Raumfahrt grant 50QM1702 ‘HRSC on Mars Express’ on behalf of the German Federal Ministry for Economic Affairs and Energy (to C.G.). The authors also thank L. Maltagliati, J. W. Head, J. F. Mustard and S. Clifford for helpful comments that improved the manuscript.

Author information

Affiliations

  1. SETI Institute, Mountain View, CA, USA

    • Janice L. Bishop
  2. National Aeronautics and Space Administration’s Ames Research Center, Moffett Field, CA, USA

    • Janice L. Bishop
  3. Centro de Astrobiología (Consejo Superior de Investigaciones Científicas–Instituto Nacional de Técnica Aeroespacial), Madrid, Spain

    • Alberto G. Fairén
  4. Cornell University, Ithaca, NY, USA

    • Alberto G. Fairén
  5. Department of Earth Sciences & Laboratory for Space Research, University of Hong Kong, Hong Kong, China

    • Joseph R. Michalski
  6. University of Vigo, Vigo, Spain

    • Luis Gago-Duport
  7. University of Idaho, Moscow, ID, USA

    • Leslie L. Baker
  8. Michigan State University, East Lansing, MI, USA

    • Michael A. Velbel
  9. Smithsonian Institution, Washington, DC, USA

    • Michael A. Velbel
  10. Freie Universität Berlin, Berlin, Germany

    • Christoph Gross
  11. National Aeronautics and Space Administration–Johnson Space Center, Houston, TX, USA

    • Elizabeth B. Rampe

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Contributions

J.L.B. generated the idea of short-term warm and wet events, performed remote sensing of Mars using orbital visible and near-infrared spectra and wrote most of the paper. A.G.F. contributed preliminary discussions defining the direction of the project and provided insights on the nature of the early Mars climate, thermodynamics of clay minerals and current Mars Science Laboratory rover results. J.R.M. provided analyses of Fe/Mg phyllosilicates from hydrothermal ocean environments and remote sensing results of Mars, and prepared figures. L.G.-D. conducted the clay synthesis modelling and prepared figures. L.L.B. contributed insights on basalt alteration and the formation of clays and poorly crystalline phases. M.A.V. provided insights on the weathering of Martian meteorites and basalt. C.G. prepared the HRSC and HiRISE images. E.B.R. contributed analyses of poorly crystalline phases of Mars in remote sensing thermal infrared emission orbital spectra and provided insights on current Mars Science Laboratory rover results regarding clays and poorly crystalline materials. All authors contributed to writing and commenting on drafts of the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Janice L. Bishop.

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https://doi.org/10.1038/s41550-017-0377-9