Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Isotopic fractionation of water and its photolytic products in the atmosphere of Mars

Nature Astronomy volume 5, pages 943–950 (2021)Cite this article

Subjects

Abstract

The current Martian atmosphere is about five times more enriched in deuterium than Earth’s, providing direct testimony that Mars hosted vastly more water in its early youth than nowadays. Estimates of the total amount of water lost to space from the current mean D/H value depend on a rigorous appraisal of the relative escape between deuterated and non-deuterated water. Isotopic fractionation of D/H between the lower and the upper atmospheres of Mars has been assumed to be controlled by water condensation and photolysis, although their respective roles in influencing the proportions of atomic D and H populations have remained speculative. Here we report HDO and H2O profiles observed by the Atmospheric Chemistry Suite (ExoMars Trace Gas Orbiter) in orbit around Mars that, once combined with expected photolysis rates, reveal the prevalence of the perihelion season for the formation of atomic H and D at altitudes relevant for escape. In addition, while condensation-induced fractionation is the main driver of variations of D/H in water vapour, the differential photolysis of HDO and H2O is a more important factor in determining the isotopic composition of the dissociation products.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Example of ACS MIR spectra and summary of the retrieval scheme.
Fig. 2: Climatology from the retrieved atmospheric parameters.
Fig. 3: Seasonal evolution of the isotopic fractionation of D/H during the photodissociation of water vapour.

Similar content being viewed by others

Data availability

The datasets generated by the ExoMars Trace Gas Orbiter instruments analysed in this study are available in the ESA Planetary Science Archive (PSA) repository, https://archives.esac.esa.int/psa, following a six months prior access period, following the ESA Rules on Information, Data and Intellectual Property. The data products generated in this study (retrieved atmospheric parameters) are available on https://github.com/juanaldayparejo/opendata.

Code availability

The spectral fitting and retrievals were performed using the NEMESIS radiative transfer and retrieval algorithm29. The code can be downloaded from https://doi.org/10.5281/zenodo.4303976

References

  1. Jakosky, B. M. Mars volatile evolution: evidence from stable isotopes. Icarus 94, 14–31 (1991).

    Article  ADS  Google Scholar 

  2. Owen, T., Maillard, J. P., de Bergh, C. & Lutz, B. L. Deuterium on Mars: the abundance of HDO and the value of D/H. Science 240, 1767–1767 (1988).

    Article  ADS  Google Scholar 

  3. Webster, C. R. et al. Isotope ratios of H, C, and O in CO2 and H2O of the Martian atmosphere. Science 341, 260–263 (2013).

    Article  ADS  Google Scholar 

  4. Villanueva, G. L. et al. Strong water isotopic anomalies in the Martian atmosphere: probing current and ancient reservoirs. Science 348, 218–221 (2015).

    Article  ADS  Google Scholar 

  5. Krasnopolsky, V. A. Variations of the HDO/H2O ratio in the Martian atmosphere and loss of water from Mars. Icarus 257, 377–386 (2015).

    Article  ADS  Google Scholar 

  6. Aoki, S. et al. Seasonal variation of the HDO/H2O ratio in the atmosphere of Mars at the middle of northern spring and beginning of northern summer. Icarus 260, 7–22 (2015).

    Article  ADS  Google Scholar 

  7. Encrenaz, T. et al. A map of D/H on Mars in the thermal infrared using EXES aboard SOFIA. Astron. Astrophys. 586, A62 (2016).

    Article  Google Scholar 

  8. Encrenaz, T. et al. New measurements of D/H on Mars using EXES aboard SOFIA. Astron. Astrophys. 612, A112 (2018).

    Article  Google Scholar 

  9. Khayat, A. S., Villanueva, G. L., Smith, M. D. & Guzewich, S. D. IRTF/CSHELL mapping of atmospheric HDO, H2O and D/H on Mars during northern summer. Icarus 330, 204–216 (2019).

    Article  ADS  Google Scholar 

  10. Vandaele, A. C. et al. Martian dust storm impact on atmospheric H2O and D/H observed by ExoMars Trace Gas Orbiter. Nature 568, 521–525 (2019).

    Article  ADS  Google Scholar 

  11. Alday, J. et al. Oxygen isotopic ratios in Martian water vapour observed by ACS MIR on board the ExoMars Trace Gas Orbiter. Astron. Astrophys. 630, A91 (2019).

    Article  Google Scholar 

  12. Villanueva, G. L. et al. Water heavily fractionated as it ascends on Mars as revealed by ExoMars/NOMAD. Sci. Adv. 7, eabc8843 (2021).

    Article  ADS  Google Scholar 

  13. Carr, M. H. & Clow, G. D. Martian channels and valleys: their characteristics, distribution, and age. Icarus 48, 91–117 (1981).

    Article  ADS  Google Scholar 

  14. Baker, V. R. Water and the Martian landscape. Nature 412, 228–236 (2001).

    Article  ADS  Google Scholar 

  15. Krasnopolsky, V. On the deuterium abundance on Mars and some related problems. Icarus 148, 597–602 (2000).

    Article  ADS  Google Scholar 

  16. Krasnopolsky, V. A. Mars’ upper atmosphere and ionosphere at low, medium, and high solar activities: implications for evolution of water. J. Geophys. Res. Planets 107, 11-1–11-11 (2002).

    Article  Google Scholar 

  17. Fox, J. L. & Hać, A. Isotope fractionation in the photochemical escape of O from Mars. Icarus 208, 176–191 (2010).

    Article  ADS  Google Scholar 

  18. Cangi, E. M., Chaffn, M. S. & Deighan, J. Higher Martian atmospheric temperatures at all altitudes increase the D/H fractionation factor and water loss. J. Geophys. Res. Planets 125, e2020JE006626 (2020).

    Article  ADS  Google Scholar 

  19. Krasnopolsky, V. A. Photochemistry of water in the Martian thermosphere and its effect on hydrogen escape. Icarus 321, 62–70 (2019).

    Article  ADS  Google Scholar 

  20. Clarke, J. T. et al. A rapid decrease of the hydrogen corona of Mars: the Martian hydrogen corona. Geophys. Res. Lett. 41, 8013–8020 (2014).

    Article  ADS  Google Scholar 

  21. Chaffin, M. S. et al. Unexpected variability of Martian hydrogen escape. Geophys. Res. Lett. 41, 314–320 (2014).

    Article  ADS  Google Scholar 

  22. Chaffin, M., Deighan, J., Schneider, N. & Stewart, A. Elevated atmospheric escape of atomic hydrogen from Mars induced by high-altitude water. Nat. Geosci. 10, 174–178 (2017).

    Article  ADS  Google Scholar 

  23. Stone, S. W. et al. Hydrogen escape from Mars is driven by seasonal and dust storm transport of water. Science 370, 824–831 (2020).

    Article  ADS  Google Scholar 

  24. Cheng, B.-M. et al. Photo-induced fractionation of water isotopomers in the Martian atmosphere. Geophys. Res. Lett. 26, 3657–3660 (1999).

    Article  ADS  Google Scholar 

  25. Merlivat, L. & Nief, G. Fractionnement isotopique lors des changements d’état solide–vapeur et liquide–vapeur de l’eau á des températures inférieures á 0 °C. Tellus 19, 122–127 (1967).

    Article  ADS  Google Scholar 

  26. Bertaux, J.-L. & Montmessin, F. Isotopic fractionation through water vapor condensation: the deuteropause, a cold trap for deuterium in the atmosphere of Mars. J. Geophys. Res. Planets 106, 32879–32884 (2001).

    Article  ADS  Google Scholar 

  27. Montmessin, F., Fouchet, T. & Forget, F. Modeling the annual cycle of HDO in the Martian atmosphere. J. Geophys. Res. Planets 110, E03006 (2005).

    Article  ADS  Google Scholar 

  28. Korablev, O. et al. The Atmospheric Chemistry Suite (ACS) of three spectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev. 214, 7 (2018).

    Article  ADS  Google Scholar 

  29. Irwin, P. et al. The NEMESIS planetary atmosphere radiative transfer and retrieval tool. J. Quant. Spectrosc. Radiat. Transf. 109, 1136–1150 (2008).

    Article  ADS  Google Scholar 

  30. Rodgers, C. D. Inverse Methods for Atmospheric Sounding: Theory and Practice (Series on Atmospheric, Oceanic and Planetary Physics Vol. 2, World Scientific, 2000).

  31. Shaposhnikov, D. S., Medvedev, A. S., Rodin, A. V. & Hartogh, P. Seasonal water ‘pump’ in the atmosphere of Mars: vertical transport to the thermosphere. Geophys. Res. Lett. 46, 4161–4169 (2019).

    Article  ADS  Google Scholar 

  32. Olsen, K. S. et al. The vertical structure of CO in the Martian atmosphere from the ExoMars Trace Gas Orbiter. Nat. Geosci. 14, 67–71 (2021).

    Article  ADS  Google Scholar 

  33. Neary, L. et al. Explanation for the increase in high-altitude water on Mars observed by NOMAD during the 2018 global dust storm. Geophys. Res. Lett. 47, e2019GL084354 (2020).

    Article  ADS  Google Scholar 

  34. Trokhimovskiy, A. et al. Mars’ water vapor mapping by the SPICAM IR spectrometer: five Martian years of observations. Icarus 251, 50–64 (2015).

    Article  ADS  Google Scholar 

  35. Fedorova, A. A. et al. Stormy water on Mars: the distribution and saturation of atmospheric water during the dusty season. Science 367, 297–300 (2020).

    Article  ADS  Google Scholar 

  36. Aoki, S. et al. Water vapor vertical profiles on Mars in dust storms observed by TGO/NOMAD. J. Geophys. Res. Planets 124, 3482–3497 (2019).

    Article  ADS  Google Scholar 

  37. Fedorova, A. et al. Multi-annual monitoring of the water vapor vertical distribution on Mars by SPICAM on Mars Express. J. Geophys. Res. Planets 126, e2020JE006616 (2020).

    ADS  Google Scholar 

  38. Montmessin, F., Forget, F., Rannou, P., Cabane, M. & Haberle, R. M. Origin and role of water ice clouds in the Martian water cycle as inferred from a general circulation model. J. Geophys. Res. Planets 109, E10004 (2004).

    Article  ADS  Google Scholar 

  39. Liuzzi, G. et al. Strong variability of Martian water ice clouds during dust storms revealed from ExoMars Trace Gas Orbiter/NOMAD. J. Geophys. Res. Planets 125, e2019JE006250 (2020).

    Article  ADS  Google Scholar 

  40. Luginin, M. et al. Properties of water ice and dust particles in the atmosphere of Mars during the 2018 global dust storm as inferred from the Atmospheric Chemistry Suite. J. Geophys. Res. Planets 125, e2020JE006419 (2020).

    Article  ADS  Google Scholar 

  41. Lamb, K. D. et al. Laboratory measurements of HDO/H2O isotopic fractionation during ice deposition in simulated cirrus clouds. Proc. Natl Acad. Sci. USA 114, 5612–5617 (2017).

    Article  ADS  Google Scholar 

  42. Majoube, M. Fractionation factor of 18O between water vapour and ice. Nature 226, 1242–1242 (1970).

    Article  ADS  Google Scholar 

  43. Casado, M. et al. Experimental determination and theoretical framework of kinetic fractionation at the water vapour–ice interface at low temperature. Geochim. Cosmochim. Acta 174, 54–69 (2016).

    Article  ADS  Google Scholar 

  44. Lefévre, F. Three-dimensional modeling of ozone on Mars. J. Geophys. Res. 109, E07004 (2004).

    ADS  Google Scholar 

  45. González-Galindo, F. Extension of a Martian general circulation model to thermospheric altitudes: UV heating and photochemical models. J. Geophys. Res. 110, E09008 (2005).

    ADS  Google Scholar 

  46. Lefévre, F. & Krasnopolsky, V. in The Atmosphere and Climate of Mars (eds Haberle, R. M. et al.) 405–432 (Cambridge University Press, 2017).

  47. Bhattacharyya, D., Clarke, J. T., Bertaux, J.-L., Chaufray, J.-Y. & Mayyasi, M. A strong seasonal dependence in the Martian hydrogen exosphere. Geophys. Res. Lett. 42, 8678–8685 (2015).

    Article  ADS  Google Scholar 

  48. Halekas, J. S. Seasonal variability of the hydrogen exosphere of Mars. J. Geophys. Res. Planets 122, 901–911 (2017).

    Article  ADS  Google Scholar 

  49. Clarke, J. T. et al. Variability of D and H in the Martian upper atmosphere observed with the MAVEN IUVS echelle channel. J. Geophys. Res. Space Phys. 122, 2336–2344 (2017).

    Article  ADS  Google Scholar 

  50. Krasnopolsky, V. A., Mumma, M. J. & Gladstone, G. R. Detection of atomic deuterium in the upper atmosphere of Mars. Science 280, 1576–1580 (1998).

    Article  ADS  Google Scholar 

  51. Miller, C. E. & Yung, Y. L. Photo-induced isotopic fractionation. J. Geophys. Res. Atmos. 105, 29039–29051 (2000).

    Article  ADS  Google Scholar 

  52. Jakosky, B. M. & Phillips, R. J. Mars’ volatile and climate history. Nature 412, 237–244 (2001).

    Article  ADS  Google Scholar 

  53. Jakosky, B. M., Pepin, R. O., Johnson, R. E. & Fox, J. Mars atmospheric loss and isotopic fractionation by solar-wind-induced sputtering and photochemical escape. Icarus 111, 271–288 (1994).

    Article  ADS  Google Scholar 

  54. Gordon, I. et al. The HITRAN2016 molecular spectroscopic database. J. Quant. Spectrosc. Radiat. Transf. 203, 3–69 (2017).

    Article  ADS  Google Scholar 

  55. Régalia, L. et al. Laboratory measurements and calculations of line shape parameters of the H2O–CO2 collision system. J. Quant. Spectrosc. Radiat. Transf. 231, 126–135 (2019).

    Article  ADS  Google Scholar 

  56. Devi, V. M. et al. Line parameters for CO2- and self-broadening in the ν1 band of HD16O. J. Quant. Spectrosc. Radiat. Transf. 203, 133–157 (2017).

    Article  ADS  Google Scholar 

  57. Devi, V. M. et al. Line parameters for CO2 broadening in the ν2 band of HD16O. J. Quant. Spectrosc. Radiat. Transf. 187, 472–488 (2017).

    Article  ADS  Google Scholar 

  58. Devi, V. M. et al. Line parameters for CO2- and self-broadening in the ν3 band of HD16O. J. Quant. Spectrosc. Radiat. Transf. 203, 158–174 (2017).

    Article  ADS  Google Scholar 

  59. Forget, F. et al. Improved general circulation models of the Martian atmosphere from the surface to above 80 km. J. Geophys. Res. Planets 104, 24155–24175 (1999).

    Article  ADS  Google Scholar 

  60. Quémerais, E. et al. Stellar occultations observed by SPICAM on Mars Express. J. Geophys. Res. 111, E09S04 (2006).

    Google Scholar 

  61. Montmessin, F. et al. Stellar occultations at UV wavelengths by the SPICAM instrument: retrieval and analysis of Martian haze profiles. J. Geophys. Res. 111, E09S09 (2006).

    Google Scholar 

  62. Irwin, P. G. et al. Probable detection of hydrogen sulphide (H2S) in Neptune’s atmosphere. Icarus 321, 550–563 (2019).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

The ExoMars mission is a joint mission of the European Space Agency (ESA) and Roscosmos. The ACS experiment is led by the Space Research Institute (IKI) in Moscow, assisted by LATMOS in France. This work was funded by Roscosmos, the National Centre for Space Studies of France (CNES), the Ministry of Science and Education of Russia, the Natural Sciences and Engineering Research Council of Canada (NSERC) (PDF 178-516895-2018) and the UK Space Agency (ST/T002069/1, ST/R001502/1 and ST/P001572/1). L.R. acknowledges the support he received from the Excellence Laboratory ‘Exploration Spatiale des Environnements Planétaires (ESEP)’ and from CNES. M.V. is supported by DIM ACAV labelled by the Île-de-France region for the research (Domaine d’Intérêt Majeur, Astrophysique et Conditions d’Apparition de la Vie). Science operations are funded by Roscosmos and ESA.

Author information

Authors and Affiliations

  1. AOPP, Department of Physics, University of Oxford, Oxford, UK

    Juan Alday, Patrick G. J. Irwin, Colin F. Wilson & Kevin S. Olsen

  2. Space Research Institute (IKI), Moscow, Russia

    Alexander Trokhimovskiy, Anna A. Fedorova, Denis A. Belyaev, Oleg Korablev, Andrey Patrakeev & Alexey Shakun

  3. LATMOS/CNRS, Guyancourt, France

    Franck Montmessin, Franck Lefévre, Margaux Vals, Loïc Rossi, Lucio Baggio & Jean-Loup Bertaux

Authors
  1. Juan Alday
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Alexander Trokhimovskiy
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Patrick G. J. Irwin
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Colin F. Wilson
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Franck Montmessin
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Franck Lefévre
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Anna A. Fedorova
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Denis A. Belyaev
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Kevin S. Olsen
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Oleg Korablev
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Margaux Vals
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Loïc Rossi
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. Lucio Baggio
    View author publications

    You can also search for this author in PubMed Google Scholar

  14. Jean-Loup Bertaux
    View author publications

    You can also search for this author in PubMed Google Scholar

  15. Andrey Patrakeev
    View author publications

    You can also search for this author in PubMed Google Scholar

  16. Alexey Shakun
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

Atmospheric retrievals from the ACS MIR spectra and interpretation of the retrieved parameters were performed by J.A. A.T., P.G.J.I., C.F.W., F.M., A.A.F., D.A.B. and K.S.O. provided input and help with spectral fitting and retrievals. Processing of the spectra was done at LATMOS by L.B. and at IKI by A.T. A.A.F. provided ACS NIR profiles for comparison and validation of the dataset. F.L. generated the photolysis rates of water vapour. F.M., F.L., O.K., M.V., L.R. and J.-L.B. provided input on the analysis and interpretation of the retrieved atmospheric parameters. The ACS instrument was operated by A.T., A.P. and A.S. All co-authors contributed to the preparation of the manuscript.

Corresponding author

Correspondence to Juan Alday.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Astronomy thanks Shohei Aoki, Vladimir Krasnopolsky and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Histogram of the measured D/H and 18O/16O isotope ratios, as well as their relation with the water vapour mixing ratio and temperature.

Only the points with uncertainties of D/H < 1 VSMOW and 18O/16O < 0.13 VSMOW are shown. The black dashed lines on the histogram plots represent typical measurement uncertainties, centred at D/H = 4.9 ± 0.4 VSMOW and 18O/16O = 1.14 ± 0.11 VSMOW. The colour of the points on the plots in the middle and right columns represents the density of measured points. The red cross in the temperature panels represents the most frequently measured value of the isotope ratios at temperatures > 180 K, which we take as the average non-fractionated isotope ratios in the Martian atmosphere.

Extended Data Fig. 2 Evolution of the water vapour mixing ratio and the D/H and 18O/16O isotopic ratios in the perihelion and aphelion seasons of MY34 and MY35.

The different panels show the retrieved profiles separated in different seasons, with the colour of the lines representing the latitude of the observations. For the clarity of the figure, only the points with uncertainties of D/H < 1 VSMOW and 18O/16O < 0.13 VSMOW are shown.

Extended Data Fig. 3 Comparison of the estimated impact of fractionation during photolysis for the perihelion and aphelion seasons during MY34 and MY35.

a, Calculated H2O dissociation rates, with the colour of the lines representing the latitude of the observations. b, Column-integrated photolysis rates (red dots) as a function of latitude. The yellow dots represent the column-integrated photolysis rates when using the part of the column in which the measurements are sensitive to HDO. c, Fractionation factor R between the D/H ratio representative of water vapour in the lower atmosphere and that of the photolysis products for the cases of photolysis-induced (black line) and condensation-induced fractionation (coloured lines). d, Column-integrated fractionation factor R as a function of latitude for the cases of photolysis-induced (blue dots) and condensation-induced (yellow dots) fractionation, as well as the combination of the two (red dots). The condensation-induced fractionation factor is only plotted if the column-integrated photolysis rate using the part of the column in which the measurements are sensitive to HDO (yellow dots in b) is at least 75% of that calculated when using the whole column (red dots in b).

Extended Data Fig. 4 Evolution of the water vapour photolysis rates and D/H fractionation factor.

a, Latitudinal coverage of the ACS MIR observations, with the colour of the points representing the column-integrated photolysis rate of H2O. b, Column-integrated photolysis rate of H2O. c, Column-integrated photolysis rates of H2O above (green dots) and below (yellow dots) 60 km. d, Column-integrated fractionation factor R for the cases of photolysis-induced (blue dots) and condensation-induced (yellow dots) fractionation, as well as the combination of the two (red dots).

Supplementary information

Supplementary Information

Supplementary information and Figs. 1–9.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Alday, J., Trokhimovskiy, A., Irwin, P.G.J. et al. Isotopic fractionation of water and its photolytic products in the atmosphere of Mars. Nat Astron 5, 943–950 (2021). https://doi.org/10.1038/s41550-021-01389-x

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41550-021-01389-x

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing