Variability in the sulfur isotopic composition in sediments can reflect atmospheric, geologic and biological processes. Evidence for ancient fluvio-lacustrine environments at Gale crater on Mars and a lack of efficient crustal recycling mechanisms on the planet suggests a surface environment that was once warm enough to allow the presence of liquid water, at least for discrete periods of time, and implies a greenhouse effect that may have been influenced by sulfur-bearing volcanic gases. Here we report in situ analyses of the sulfur isotopic compositions of SO2 volatilized from ten sediment samples acquired by NASA’s Curiosity rover along a 13 km traverse of Gale crater. We find large variations in sulfur isotopic composition that exceed those measured for Martian meteorites and show both depletion and enrichment in 34S. Measured values of δ34S range from −47 ± 14‰ to 28 ± 7‰, similar to the range typical of terrestrial environments. Although limited geochronological constraints on the stratigraphy traversed by Curiosity are available, we propose that the observed sulfur isotopic signatures at Gale crater can be explained by equilibrium fractionation between sulfate and sulfide in an impact-driven hydrothermal system and atmospheric processing of sulfur-bearing gases during transient warm periods.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    et al. Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars. Science 350, AAC7575 (2015).

  2. 2.

    et al. Gale Crater: formation and post-impact hydrous environments. Planet. Space Sci. 70, 84–95 (2012).

  3. 3.

    & Impact-induced hydrothermal activity on early Mars. J. Geophys. Res. 110, E12S09 (2005).

  4. 4.

    et al. Impact-generated hydrothermal systems on Earth and Mars. Icarus 224, 347–363 (2013).

  5. 5.

    , , & The missing organic molecules on Mars. Proc. Natl Acad. Sci. USA 97, 2425–2430 (2000).

  6. 6.

    et al. Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars. Nature 508, 364–368 (2014).

  7. 7.

    , , & Evidence of atmospheric sulphur in the Martian regolith from sulphur isotopes in meteorites. Nature 404, 50–52 (2000).

  8. 8.

    , & Implications from sulfur isotopes of the Nakhla meteorite for the origin of sulfate on Mars. Earth Planet. Sci. Lett. 264, 1–8 (2007).

  9. 9.

    , & Sulfide isotopic compositions in shergottites and ALH 84001, and possible implications for life on Mars. Geochim. Cosmochim. Acta 61, 4449–4453 (1997).

  10. 10.

    , , & Modified sulfur isotopic compositions of sulfides in the nakhlites and Chassigny. Geochim. Cosmochim. Acta 64, 1121–1131 (2000).

  11. 11.

    , & Sulfur isotopic compositions of individual sulfides in Martian meteorites ALH 84001 and Nakhla: implications for crust-regolith exchange on Mars. Earth Planet. Sci. Lett. 184, 23–35 (2000).

  12. 12.

    , , & Sulfur isotopic systematics in alteration assemblages in Martian meteorite Allan Hills 84001. Geochim. Cosmochim. Acta 60, 2921–2926 (1996).

  13. 13.

    in Sulfide Mineralogy and Geochemistry Vol. 61 (ed. Vaughan, D. J.) 633–677 (Min. Soc. Amer., 2006).

  14. 14.

    et al. Mineralogy of a mudstone at Yellowknife Bay, Gale Crater, Mars. Science 343, 1243480 (2014).

  15. 15.

    et al. Calcium sulfate veins characterized by ChemCam/Curiosity at Gale crater, Mars. J. Geophys. Res. 119, 1991–2016 (2014).

  16. 16.

    , & Theoretical estimates of equilibrium sulfur isotope effects in aqueous sulfur systems: highlighting the role of isomers in the sulfite and sulfoxylate systems. Geochim. Cosmochim. Acta 195, 171–200 (2016).

  17. 17.

    et al. Fluids during diagenesis and sulfate vein formation in sediments at Gale crater Mars. Met. Planet. Sci. 51, 2175–2202 (2016).

  18. 18.

    et al. Sulfur isotope signatures for rapid colonization of an impact crater by thermophilic microbes. Geology 38, 271–274 (2010).

  19. 19.

    et al. Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars. J. Geophys. Res. 120, 495–514 (2015).

  20. 20.

    , , & Mass-independent fractionation of sulfur isotopes during broadband SO2 photolysis: comparison between 16O- and 18O-rich SO2. Chem. Geol. 362, 56–65 (2013).

  21. 21.

    , , & Sulfur isotopic fractionation in vacuum UV photodissociation of hydrogen sulfide and its potential relevance to meteorite analysis. Proc. Natl Acad. Sci. USA 110, 17650–17655 (2013).

  22. 22.

    , , & Rare sulfur and triple oxygen isotope geochemistry of volcanogenic sulfate aerosols. Geochim. Cosmochim. Acta 71, 2326–2343 (2007).

  23. 23.

    UV induced mass-independent sulfur isotope fractionation in stratospheric volcanic sulfate. Geophys. Res. Lett. 30, 2131 (2003).

  24. 24.

    & Episodic warming of early Mars by punctutated volcanism. Nat. Geosci. 7, 865–868 (2014).

  25. 25.

    , & Sulfur isotopic fractionation in the gas-phase oxidation of sulfur dioxide initiated by hydroxyl radicals. J. Phys. Chem. A 105, 8073–8076 (2001).

  26. 26.

    & in Geochemistry of Hydrothermal Ore Deposits (ed. Barnes, H. L.) 509–567 (John Wiley, 1997).

  27. 27.

    , & Fate of SO2 in the ancient Martian atmosphere: implications for transient greenhouse warming. J. Geophys. Res. 114, E11011 (2009).

  28. 28.

    et al. Diagenetic origin of nodules in the Sheepbed member, Yellowknife Bay formation, Gale crater, Mars. J. Geophys. Res. 119, 1637–1664 (2014).

  29. 29.

    et al. Multiple stages of aqueous alteration along fractures in mudstone and sandstone strata in Gale Crater, Mars. Earth Planet. Sci. Lett. 471, 186–198 (2017).

  30. 30.

    et al. Light and variable 37Cl/35Cl ratios in rocks from Gale Crater, Mars: possible signature of perchlorate. Earth Planet. Sci. Lett. 438, 14–24 (2016).

  31. 31.

    et al. Analytical techniques for retrieval of atmospheric composition with the quadrupole mass spectrometer of the Sample Analysis at Mars instrument suite on Mars Science Laboratory. Planet. Space Sci. 96, 99–113 (2014).

  32. 32.

    et al. Calibrated sulfur isotope abundance ratios of three IAEA sulfur isotope reference materials and V-CDT with a reassessment of the atomic weight of sulfur. Geochim. Cosmochim. Acta 65, 2433–2437 (2001).

Download references


This work was funded by NASA’s Mars Exploration Program. The authors thank T. B. Griswold for assistance with figure preparation, B. Franz for editorial support, J. Farquhar for manuscript review, J. Farquhar and A. J. Kaufman for facilitating isotopic analyses of calibrants, and the technical team at the NASA GSFC Planetary Environments Laboratory for laboratory support.

Author information


  1. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

    • H. B. Franz
    • , A. C. McAdam
    • , C. Freissinet
    • , P. R. Mahaffy
    • , P. G. Conrad
    • , J. L. Eigenbrode
    • , D. P. Glavin
    • , C. A. Knudson
    • , A. A. Pavlov
    •  & J. C. Stern
  2. NASA Johnson Space Center, Houston, Texas 77058, USA

    • D. W. Ming
    • , P. D. Archer Jr
    • , R. V. Morris
    • , E. B. Rampe
    •  & B. Sutter
  3. Center for Space Science and Technology, University of Maryland Baltimore County, Baltimore, Maryland 21250, USA

    • C. Freissinet
  4. Department of Geology, University of Maryland, College Park, Maryland 20742, USA

    • D. L. Eldridge
    • , J. W. Dottin III
    •  & R. Plummer
  5. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA

    • W. W. Fischer
    • , J. P. Grotzinger
    •  & K. A. Farley
  6. Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA

    • C. H. House
  7. Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, USA

    • J. A. Hurowitz
    •  & S. M. McLennan
  8. Department of Environment, Earth and Ecosystems, The Open University, Milton Keynes MK7 6AA, UK

    • S. P. Schwenzer
  9. Planetary Science Institute, Tucson, Arizona 85719, USA

    • D. T. Vaniman
  10. Jacobs Technology, Houston, Texas 77058, USA

    • P. D. Archer Jr
    •  & B. Sutter
  11. Department of Climate and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA

    • S. K. Atreya
  12. Department of Biology/STIA, Georgetown University, Washington DC 20057, USA

    • S. S. Johnson
  13. Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA

    • C. A. Knudson
  14. Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Cuidad Universitaria, Mexico City 04510, Mexico

    • R. Navarro-González
  15. Aerodyne Industries, Houston, Texas 77058, USA

    • E. B. Rampe
  16. Geophysical Laboratory, Carnegie Institute of Washington, Washington DC 20015, USA

    • A. Steele
  17. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • R. E. Summons


  1. Search for H. B. Franz in:

  2. Search for A. C. McAdam in:

  3. Search for D. W. Ming in:

  4. Search for C. Freissinet in:

  5. Search for P. R. Mahaffy in:

  6. Search for D. L. Eldridge in:

  7. Search for W. W. Fischer in:

  8. Search for J. P. Grotzinger in:

  9. Search for C. H. House in:

  10. Search for J. A. Hurowitz in:

  11. Search for S. M. McLennan in:

  12. Search for S. P. Schwenzer in:

  13. Search for D. T. Vaniman in:

  14. Search for P. D. Archer Jr in:

  15. Search for S. K. Atreya in:

  16. Search for P. G. Conrad in:

  17. Search for J. W. Dottin III in:

  18. Search for J. L. Eigenbrode in:

  19. Search for K. A. Farley in:

  20. Search for D. P. Glavin in:

  21. Search for S. S. Johnson in:

  22. Search for C. A. Knudson in:

  23. Search for R. V. Morris in:

  24. Search for R. Navarro-González in:

  25. Search for A. A. Pavlov in:

  26. Search for R. Plummer in:

  27. Search for E. B. Rampe in:

  28. Search for J. C. Stern in:

  29. Search for A. Steele in:

  30. Search for R. E. Summons in:

  31. Search for B. Sutter in:


H.B.F. developed analytical methods, calculated and interpreted sulfur isotope ratios, performed calibration experiments, and wrote the manuscript and most of the Supplementary Information. A.C.M. wrote the mineralogy section of the Supplementary Information. H.B.F., A.C.M. and C.A.K. performed supporting laboratory EGA studies. C.F. contributed to analysis of calibration data. D.L.E. calculated theoretical equilibrium fractionation factors for relevant sulfur-bearing species. H.B.F., J.W.D. and R.P. performed ground-truth isotopic analyses of calibrants. All authors participated in discussion of results and/or editing of the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to H. B. Franz.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Information

  2. 2.

    Supplementary Tables

    Supplementary data tables 1–4 (this file was missing when this Article was originally published).

About this article

Publication history