Abstract

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today1. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations2,3,4,5. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere6,7, which—given methane’s lifetime of several centuries—predicts an even, well mixed distribution of methane1,6,8. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections2,4. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally.

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Data availability

The datasets generated by the NOMAD and ACS instruments and analysed during the current study will be available in the ESA Planetary Science Archive repository, https://archives.esac.esa.int/psa, after the six months prior access period, following the ESA Rules on Information, Data and Intellectual Property. The data used for the figures are available on request from the corresponding author.

Code availability

The computer codes used to decipher the upper limits of CH4 are available on request from the corresponding author.

Additional information

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

Change history

  • 17 April 2019

    The surname of author Cathy Quantin-Nataf was misspelled ‘Quantin-Nata’, authors Ehouarn Millour and Roland Young were missing from the ACS and NOMAD Science Teams list, and minor changes have been made to the author and affiliation lists; see accompanying Amendment. These errors have been corrected online.

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Acknowledgements

ExoMars is the space mission of ESA and Roscosmos. The ACS experiment is led by IKI, the Space Research Institute in Moscow, assisted by LATMOS in France. The project acknowledges funding by Roscosmos and CNES. The science operations of ACS are funded by Roscosmos and ESA. IKI affiliates acknowledge funding under grant number 14.W03.31.0017 and contract number 0120.0 602993 (0028-2014-0004) of the Russian government. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (BIRA-IASB), assisted by co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the UK (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination of the ESA Prodex Office (PEA 4000103401 and PEA 4000121493), by Spanish MICINN through its Plan Nacional and by European funds under grants ESP2015-65064-C2-1-P and ESP2017-87143-R (MINECO/FEDER), as well as by the UK Space Agency through grants ST/R005761/1, ST/P001262/1, ST/R001405/1, ST/S00145X/1, ST/R001367/1, ST/P001572/1 and ST/R001502/1, and the Italian Space Agency through grant 2018-2-HH.0. This work was supported by the Belgian Fonds de la Recherche Scientifique—FNRS under grant number 30442502 (ET_HOME). We are indebted to the large number of people responsible for designing, building, testing, launching, communicating to and operating the spacecraft and science instruments, whose efforts made the success of TGO possible.

Reviewer information

Nature thanks Jonathan Lunine, John Moores, Kevin Zahnle and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information

Author notes

  1. A list of participants and their affiliations appears at the end of the paper.

Affiliations

  1. Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia

    • Oleg Korablev
    • , Anna A. Fedorova
    • , Alexander Trokhimovskiy
    • , Alexey V. Grigoriev
    • , Nikolay I. Ignatiev
    • , Alexey Shakun
    • , Andrey Patrakeev
    • , Denis A. Belyaev
    • , Jean-Loup Bertaux
    • , Lev Zelenyi
    • , Konstantin Anufreychik
    • , Igor Khatuntsev
    • , Nikita Kokonkov
    • , Ruslan Kuzmin
    • , Mikhail Luginin
    • , Igor Maslov
    • , Boris Moshkin
    • , Dmitry Patsaev
    •  & Ludmila Zasova
  2. Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium

    • Ann Carine Vandaele
    • , Frank Daerden
    • , Ian R. Thomas
    • , Loïc Trompet
    • , Justin T. Erwin
    • , Shohei Aoki
    • , Séverine Robert
    • , Lori Neary
    • , Sébastien Viscardy
    • , Bojan Ristic
    • , Yannick Willame
    • , Cédric Depiesse
    • , Laszlo Hetey
    • , Sophie Berkenbosch
    • , Roland Clairquin
    • , Claudio Queirolo
    • , Bram Beeckman
    • , Eddy Neefs
    • , David Bolsée
    • , Fabiana Da Pieve
    • , Didier Fussen
    • , Arnaud Mahieux
    • , Arianna Piccialli
    •  & Valérie Wilquet
  3. Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Paris, France

    • Franck Montmessin
    • , Franck Lefèvre
    • , Jean-Loup Bertaux
    • , Kevin S. Olsen
    • , Lucio Baggio
    • , Gaétan Lacombe
    • , Anni Määttänen
    •  & Emmanuel Marcq
  4. Laboratoire de Météorologie Dynamique (LMD), CNRS Jussieu, Paris, France

    • François Forget
    • , Sandrine Guerlet
    • , Ehouarn Millour
    •  & Roland Young
  5. Department of Physics, Oxford University, Oxford, UK

    • Juan Alday
    •  & Colin F. Wilson
  6. Main Astronomical Observatory (MAO), National Academy of Sciences of Ukraine, Kiev, Ukraine

    • Yuriy S. Ivanov
  7. School of Physical Sciences, The Open University, Milton Keynes, UK

    • Jon Mason
    • , Manish R. Patel
    • , James Holmes
    •  & Stephen Lewis
  8. Instituto de Astrofisica e Planetologia Spaziali, INAF, Rome, Italy

    • Giancarlo Bellucci
    • , Giuseppe Etiope
    • , Francesca Altieri
    • , Giacomo Carrozzo
    • , Emiliano D’Aversa
    • , Marco Giuranna
    • , Davide Grassi
    • , Fabrizio Oliva
    •  & Paulina Wolkenberg
  9. Instituto de Astrofìsica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Granada, Spain

    • Jose-Juan López-Moreno
    • , Bernd Funke
    • , Maia Garcia-Comas
    • , Francisco Gonzalez-Galindo
    • , Manuel López-Puertas
    •  & Miguel López-Valverde
  10. Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy

    • Giuseppe Etiope
  11. Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania

    • Giuseppe Etiope
  12. European Space Research and Technology Centre (ESTEC), ESA, Noordwijk, The Netherlands

    • Håkan Svedhem
    •  & Jorge L. Vago
  13. Instituto Universitario de Microgravedad, Universidad Politécnica de Madrid (IDR-UPM), Madrid, Spain

    • Gustavo Alonso-Rodrigo
  14. Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institute of Planetary Research, Berlin, Germany

    • Gabriele Arnold
  15. Université Libre de Bruxelles, Brussels, Belgium

    • Sophie Bauduin
    •  & Jean Vander Auwera
  16. Space Science Institute, Boulder, CO, USA

    • R. Todd Clancy
    •  & Michael J. Wolff
  17. Department of Geography, University of Winnipeg, Winnipeg, Canada

    • Edward Cloutis
  18. NASA Goddard Space Flight Center, Greenbelt, MD, USA

    • Matteo Crismani
    • , Giuliano Liuzzi
    • , Michael J. Mumma
    • , Robert E. Novak
    • , Michael D. Smith
    •  & Geronimo Villanueva
  19. Moscow University, Moscow, Russia

    • Natalia Duxbury
  20. Laboratoire d’études spatiales et d’instrumentation en astrophysique (LESIA), Observatoire de Paris-Meudon, Paris, France

    • Therese Encrenaz
    • , Thierry Fouchet
    •  & Emmanuel Lellouch
  21. Laboratory for Planetary and Atmospheric Physics (LPAP), University of Liège, Liège, Belgium

    • Jean-Claude Gérard
    • , Leo Gkouvelis
    • , Benoît Hubert
    •  & Birgit Ritter
  22. Max Planck Institute, Göttingen, Germany

    • Paul Hartogh
    •  & Alexander Medvedev
  23. Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland

    • Jacek Kaminski
  24. Royal Observatory of Belgium, Brussels, Belgium

    • Ozgur Karatekin
  25. Tohoku University, Sendai, Japan

    • Yasumasa Kasaba
    •  & Hiromu Nakagawa
  26. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    • David Kass
    •  & Armin Kleinböhl
  27. Catholic University of America, Washington, DC, USA

    • Vladimir Krasnopolsky
  28. School of Fundamental and Applied Physics, Moscow Institute of Physics and Technology (MIPT), Moscow, Russia

    • Vladimir Krasnopolsky
    •  & Alexander Rodin
  29. Vernadsky Institute, Russian Academy of Sciences (RAS), Moscow, Russia

    • Ruslan Kuzmin
  30. Agenzia Spaziale Italiana (ASI), Rome, Italy

    • Orietta Lanciano
  31. Luleå University of Technology, Luleå, Sweden

    • Javier Martin-Torres
    •  & Maria Paz Zorzano
  32. Instituto Andaluz de Ciencias de la Tierra, Universidad de Granada, Granada, Spain

    • Javier Martin-Torres
  33. Laboratoire de Géologie de Lyon, Université Claude Bernard, Lyon, France

    • Cathy Quantin-Nataf
  34. Advanced Mechanical and Optical Systems (AMOS), Liège, Belgium

    • Etienne Renotte
  35. Geosciences Paris Sud (GEOPS), Université Paris Sud, Orsay, France

    • Frédéric Schmidt
  36. Laboratory for Atmospheric and Space Physics (LASP), Boulder, CO, USA

    • Nick Schneider
    •  & Ed Thiemann
  37. Institute of Astronomy, Russian Academy of Sciences (RAS), Moscow, Russia

    • Valery Shematovich
  38. School of Earth Sciences, University of Bristol, Bristol, UK

    • Nicholas A. Teanby
  39. University of Bern, Bern, Switzerland

    • Nicolas Thomas
  40. Universidad Complutense de Madrid, Madrid, Spain

    • Luis Vazquez
  41. Institut d’Astrophysique Spatiale (IAS), Université Paris Sud, Orsay, France

    • Matthieu Vincendon
  42. Centre for Research in Earth and Space Science, York University, Toronto, Canada

    • James Whiteway
  43. Lunar and Planetary Laboratory (LPL), University of Arizona, Tucson, AZ, USA

    • Roger Yelle
  44. Centro de Astrobiología, Instituto Nacional de Técnica Aeroespacial (CSIC/INTA), Madrid, Spain

    • Maria Paz Zorzano

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Consortia

  1. The ACS and NOMAD Science Teams

Contributions

O.K., A.C.V. and F.M. conceived the study, collected inputs and wrote the paper. A.A.F. calibrated the ACS data and analysed the profiles (assisted by A.T., K.S.O. and J.A.). The ACS dataset was prepared by A.T. (assisted by L.B., J.A. and Y.S.I.). A.T., A.V.G., N.I.I., A.S. and A.P. designed the ACS observations. D.A.B. analysed the ACS CO2 data. F.M. derived the methane detection limits from ACS. I.R.T. analysed the solar occultation data and provided transmittances from the NOMAD SO channel. J.T.E. and L.T., with S.A., derived the NOMAD methane detection limits. The initial General Circulation Model fields were provided by L.N. and F.D., and J.T.E. and S.R. provided and analysed the a priori knowledge and initial General Circulation Model fields. C.D. and Y.W. were involved in UVIS calibration and the data pipeline. B.R., B.B., C.Q. and E.N. designed the NOMAD observations, helped by J.M. for the UVIS channel. L.H., S.B. and R.C. are responsible for the uplink and downlink of telemetry and science data, and the first conversion of those data. M.R.P., G.B. and J.-J.L.-M. provided support in the selection of the NOMAD observations on the basis of their scientific interest. F.F., F.L. and F.D. provided critical inputs regarding the model chemistry and circulation (assisted by J.-L.B. L.N., S.V. and G.E.). C.F.W., L.Z., H.S. and J.L.V. coordinated observations of the various instruments on TGO. All authors contributed to the preparation of the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Oleg Korablev.

Extended data figures and tables

  1. Extended Data Fig. 1 A sequence of transmittance spectra measured with the ACS MIR channel.

    The spectra are for an example orbit (Lsolar = 180.9°) obtained using the secondary grating position 12 (ref. 17). Different diffraction orders (top axis) are denoted by the changing colour of the transmission curves, and their numbers are indicated on the upper scale. Diffraction orders used in this study are 178 (for CO2), 180 (the CH4 Q-branch), and 182 (the CH4 R-branch). Enhanced extinction on the short wavelength edge of the spectra is due to H2O ice absorption.

  2. Extended Data Fig. 2 Retrieval of trace gases from ACS MIR spectra using Rodger’s regression.

    The spectra are for one aerosol-free polar case (upper panels), and for a more cloudy low-latitude case (lower panels). Both occultations were observed before the global dust event. Left-hand-side panels show water vapour profiles retrieved using faint H2O absorption lines separately in diffraction orders 180 and 182. Middle panels show attempts to retrieve CH4 in the same diffraction orders (order 180 gives access to the CH4 Q-branch, and order 182 to the CH4 R-branch). Curves with error bars indicate the regularized profiles (denoted as Tikhonov Qb). The error bars give the 1σ uncertainty on the retrieved parameters. To illustrate the accuracy for the individual spectra, the regularization was also turned off (scatter points). Right-hand-side panels show profiles for the optical depth on the line of sight (red), and of the SNR in the MIR spectra (black). The SNR for each spectrum was calculated over the whole diffraction order, excluding spectral intervals with gaseous features.

  3. Extended Data Fig. 3 Theoretical relation between the instrument SNR and the methane detection limit, and the step-by-step outputs of the CH4 retrieval.

    Top panel, the theoretical relation between SNR per pixel and the retrieved 1σ uncertainty on the CH4 line-of-sight density expressed in units of molecules per cm2. At SNR >1,000 per pixel, the associated uncertainty is 1014 molecules per cm2, which would yield an equivalent vmr uncertainty of 0.1 p.p.b.v. of CH4 in the 10-km altitude range where the CO2 density is usually around 1024 molecules per cm2. Bottom panels (from left to right), altitude profiles of SNR per pixel (left), CO2 and the error on the CH4 line-of-sight (LOS) density in units of cm−2 (middle) and the resulting upper limits retrieved for CH4 molecules (right). The displayed observation corresponds to high northern latitudes after the equinox (Lsolar 192°; 13 June 2018). The prevailing clear conditions allowed sounding very close to the surface with high SNR, yielding optimal conditions for the retrieval of CH4. The black, red and blue colours refer respectively to CO2 (in order 178), CH4 (in order 180) and CH4 (in order 182).

  4. Extended Data Fig. 4 A compilation of all the retrieved upper limits from the ACS-MIR dataset covering the period from 21 April to 4 September 2018.

    Top, limits from the Q-branch of CH4 absorption; bottom, limits from the R-branch of CH4 absorption. The colour scale denotes Lsolar. Different symbols of similar colour designate individual profiles.

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DOI

https://doi.org/10.1038/s41586-019-1096-4

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