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Background levels of methane in Mars’ atmosphere show strong seasonal variations

Christopher R. Webster https://orcid.org/0000-0003-3448-9783 [email protected], Paul R. Mahaffy https://orcid.org/0000-0003-1896-1726, Sushil K. Atreya, John E. Moores https://orcid.org/0000-0001-9435-1095, Gregory J. Flesch https://orcid.org/0000-0001-5949-1586, Charles Malespin https://orcid.org/0000-0002-5852-5016, Christopher P. McKay https://orcid.org/0000-0002-6243-1362, German Martinez https://orcid.org/0000-0001-5885-236X, Christina L. Smith, Javier Martin-Torres, Javier Gomez-Elvira https://orcid.org/0000-0002-4492-9650, Maria-Paz Zorzano, Michael H. Wong https://orcid.org/0000-0003-2804-5086, Melissa G. Trainer https://orcid.org/0000-0003-1106-8580, Andrew Steele https://orcid.org/0000-0001-9643-2841, Doug Archer Jr., Brad Sutter https://orcid.org/0000-0002-3036-170X, Patrice J. Coll https://orcid.org/0000-0003-4184-4640, Caroline Freissinet, Pierre-Yves Meslin https://orcid.org/0000-0002-0703-3951, Raina V. Gough https://orcid.org/0000-0003-2755-7282, Christopher H. House, Alexander Pavlov https://orcid.org/0000-0001-8771-1646, Jennifer L. Eigenbrode https://orcid.org/0000-0003-3089-1986, Daniel P. Glavin https://orcid.org/0000-0001-7779-7765, John C. Pearson, Didier Keymeulen https://orcid.org/0000-0003-2990-724X, Lance E. Christensen, Susanne P. Schwenzer https://orcid.org/0000-0002-9608-0759, Rafael Navarro-Gonzalez https://orcid.org/0000-0002-6078-7621, Jorge Pla-García, Scot C. R. Rafkin, Álvaro Vicente-Retortillo, Henrik Kahanpää https://orcid.org/0000-0001-9108-186X, Daniel Viudez-Moreiras https://orcid.org/0000-0001-8442-3788, Michael D. Smith https://orcid.org/0000-0002-7601-1158, Ari-Matti Harri https://orcid.org/0000-0001-8541-2802, Maria Genzer https://orcid.org/0000-0002-3971-0152, Donald M. Hassler https://orcid.org/0000-0001-8830-1200, Mark Lemmon https://orcid.org/0000-0002-4504-5136, Joy Crisp https://orcid.org/0000-0002-3202-4416, Stanley P. Sander https://orcid.org/0000-0003-1424-3620, Richard W. Zurek https://orcid.org/0000-0003-1424-9723, and Ashwin R. Vasavada https://orcid.org/0000-0003-2665-286X
Science • 8 Jun 2018 • Vol 360, Issue 6393 • pp. 1093-1096 • DOI: 10.1126/science.aaq0131
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Measuring martian organics and methane

The Curiosity rover has been sampling on Mars for the past 5 years (see the Perspective by ten Kate). Eigenbrode et al. used two instruments in the SAM (Sample Analysis at Mars) suite to catch traces of complex organics preserved in 3-billion-year-old sediments. Heating the sediments released an array of organics and volatiles reminiscent of organic-rich sedimentary rock found on Earth. Most methane on Earth is produced by biological sources, but numerous abiotic processes have been proposed to explain martian methane. Webster et al. report atmospheric measurements of methane covering 3 martian years and found that the background level varies with the local seasons. The seasonal variation provides an important clue for determining the origin of martian methane.
Science, this issue p. 1096, p. 1093; see also p. 1068

Abstract

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.

Supplementary Material

Summary

Materials and Methods
Supplementary Text
Figs. S1 to S44
Tables S1 and S2
References (48–62)

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References and Notes

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8 June 2018

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Acknowledgments

The authors thank the reviewers for constructive comments that greatly improved the manuscript. The research described here was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). Funding: Funding from NASA’s Planetary Science Division is acknowledged by authors C.R.W., P.R.M., S.K.A., G.J.F., C.M., C.P.M., M.H.W., M.G.T., A.S., D.A., C.H.H., R.V.G., A.P., J.L.E., D.P.G., J.C.P., D.K., L.E.C., J.P.-G., S.C.R.R., M.D.S., D.M.H., M.L., J.C., R.W.Z., and A.R.V. R.N.-G. acknowledges funding from the National Autonomous University of Mexico and Consejo Nacional de Ciencia y Tecnología. J.E.M. and C.L.S. acknowledge funding from the Canadian Space Agency MSL participating scientist program. S.P.Sc. acknowledges funding from the UK Space Agency. A.-M.H. acknowledges funding from the Finnish Academy under grant 310509. J.P.-G. acknowledges funding from the Spanish Ministry of Economy and Competitiveness under contract ESP2016-79612-C3-1-R. Author contributions: C.R.W. and P.R.M. performed TLS-SAM instrument design, build, and testing (IDBT); surface operations (SO); test-bed activities (TBA); data analysis (DA); data correlations (DC); and science interpretation (SI). G.J.F. and C.M. performed IDBT, SO, TBA, and DA. S.K.A., J.E.M., C.P.M., C.L.S., A.S., D.A., B.S., P.J.C., C.F., P.-Y.M., R.V.G., C.H.H., A.P., J.L.E., D.P.G., S.P.Sa., and R.W.Z. performed SI. J.C. and A.R.V. performed SO. J.C.P., D.K., and L.E.C. performed IDBT. G.M., J.M.-T., J.G.-E., M.-P.Z., M.G.T., S.P.Sc., R.N.-G., A.V.-R., H.K., D.V.-M., M.D.S., A.-M.H., M.G., D.M.H., and M.L. performed DC. J.P.-G. and S.C.R.R. performed DC and SI. Competing interests: No potential conflicts of interest exist for any of the listed authors. Data and materials availability: The data described in this paper are publicly available from NASA’s Planetary Data System (PDS) under an arrangement with the Mars Science Laboratory (MSL) project at http://pds-geosciences.wustl.edu/missions/msl/sam.htm, under the run numbers given in table S2.

Authors

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Christopher R. Webster* https://orcid.org/0000-0003-3448-9783 [email protected]
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Paul R. Mahaffy https://orcid.org/0000-0003-1896-1726
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
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Sushil K. Atreya
Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA.
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John E. Moores https://orcid.org/0000-0001-9435-1095
Department of Earth and Space Science and Engineering, York University, Toronto, ON, Canada.
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Gregory J. Flesch https://orcid.org/0000-0001-5949-1586
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Charles Malespin https://orcid.org/0000-0002-5852-5016
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
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Christopher P. McKay https://orcid.org/0000-0002-6243-1362
NASA Ames Research Center, Moffett Field, CA, USA.
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German Martinez https://orcid.org/0000-0001-5885-236X
Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA.
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Christina L. Smith
Department of Earth and Space Science and Engineering, York University, Toronto, ON, Canada.
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Javier Martin-Torres
Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Luleå, Sweden.
Instituto Andaluz de Ciencias de la Tierra, Granada, Spain.
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Javier Gomez-Elvira https://orcid.org/0000-0002-4492-9650
Centro de Astrobiología, Instituto National de Tecnica Aerospacial, Madrid, Spain.
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Maria-Paz Zorzano
Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Luleå, Sweden.
Centro de Astrobiología, Instituto National de Tecnica Aerospacial, Madrid, Spain.
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Michael H. Wong https://orcid.org/0000-0003-2804-5086
Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA.
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Melissa G. Trainer https://orcid.org/0000-0003-1106-8580
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
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Andrew Steele https://orcid.org/0000-0001-9643-2841
Geophysical Laboratory, Carnegie Institution for Science, Washington, DC, USA.
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Doug Archer Jr.
Jacobs Technology, NASA Johnson Space Center, Houston, TX, USA.
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Brad Sutter https://orcid.org/0000-0002-3036-170X
Jacobs Technology, NASA Johnson Space Center, Houston, TX, USA.
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Patrice J. Coll https://orcid.org/0000-0003-4184-4640
Laboratoire Interuniversitaire des Systèmes Atmosphériques, Creteil Cedex, France.
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Caroline Freissinet
Laboratoire Atmosphères, Milieux, Observations Spatiales, Paris Cedex 05, France.
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Pierre-Yves Meslin https://orcid.org/0000-0002-0703-3951
Institut de Recherche en Astrophysique et Planétologie, Toulouse, France.
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Raina V. Gough https://orcid.org/0000-0003-2755-7282
Department of Chemistry and Biochemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA.
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Christopher H. House
Department of Geosciences, Pennsylvania State University, University Park, PA, USA.
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Alexander Pavlov https://orcid.org/0000-0001-8771-1646
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
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Jennifer L. Eigenbrode https://orcid.org/0000-0003-3089-1986
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
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Daniel P. Glavin https://orcid.org/0000-0001-7779-7765
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
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John C. Pearson
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Didier Keymeulen https://orcid.org/0000-0003-2990-724X
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Lance E. Christensen
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Susanne P. Schwenzer https://orcid.org/0000-0002-9608-0759
School of Environment, Earth and Ecosystem Sciences, Open University, Milton Keynes, UK.
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Rafael Navarro-Gonzalez https://orcid.org/0000-0002-6078-7621
Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico City, Mexico.
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Jorge Pla-García
Centro de Astrobiología, Instituto National de Tecnica Aerospacial, Madrid, Spain.
Space Science Institute, Boulder, CO, USA.
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Scot C. R. Rafkin
Department of Space Studies, Southwest Research Institute Boulder, Boulder, CO, USA.
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Álvaro Vicente-Retortillo
Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA.
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Henrik Kahanpää https://orcid.org/0000-0001-9108-186X
Finnish Meteorological Institute, Helsinki, Finland.
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Daniel Viudez-Moreiras https://orcid.org/0000-0001-8442-3788
Centro de Astrobiología, Instituto National de Tecnica Aerospacial, Madrid, Spain.
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Michael D. Smith https://orcid.org/0000-0002-7601-1158
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
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Ari-Matti Harri https://orcid.org/0000-0001-8541-2802
Finnish Meteorological Institute, Helsinki, Finland.
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Maria Genzer https://orcid.org/0000-0002-3971-0152
Finnish Meteorological Institute, Helsinki, Finland.
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Donald M. Hassler https://orcid.org/0000-0001-8830-1200
Department of Space Studies, Southwest Research Institute Boulder, Boulder, CO, USA.
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Mark Lemmon https://orcid.org/0000-0002-4504-5136
Department of Atmospheric Sciences, Texas A&M University, College Station, TX, USA.
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Joy Crisp https://orcid.org/0000-0002-3202-4416
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Stanley P. Sander https://orcid.org/0000-0003-1424-3620
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Richard W. Zurek https://orcid.org/0000-0003-1424-9723
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Ashwin R. Vasavada https://orcid.org/0000-0003-2665-286X
NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
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Notes

*Corresponding author. Email: [email protected]

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Science
Volume 360|Issue 6393
8 June 2018
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Accepted:4 May 2018
Published in print:8 June 2018
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Cited by
    • Thasshwin Mathanlal,
    • Anshuman Bhardwaj,
    • Abhilash Vakkada Ramachandran,
    • María-Paz Zorzano,
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    Subsurface robotic exploration for geomorphology, astrobiology and mining during MINAR6 campaign, Boulby Mine, UK: part II (Results and Discussion), International Journal of Astrobiology, 20, 1, (93-108), (2021).https://doi.org/10.1017/S1473550420000385
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Jumping to conclusions
Ewan Cameron
  • Statistician
  • University of Oxford

I worry that the key claim of this article ("The background levels of methane ... exhibit a strong, repeatable seasonal variation.") is in fact only weakly supported (< a 1.5 "sigma" claim) by the available evidence from a statistical point of view. As far as I can see there is no statistical modelling conducted herein to test the stated hypothesis against alternatives, nor a clear quantification of what specifically is considered "strong" and "seasonal" from a mathematical point of view. One way to quantify the shape of the signal perhaps seen in this dataset would be to examine the Bayesian posterior in the amplitude of a sinusoidal annual trend. Constructing this posterior myself with a regular Bayesian analysis suggests a 15% subjective probability that the amplitude is less than 0.1 ppbv, although even to choose that threshold as the boundary of "strong" variation might be too (generously) low. Bayesian bagging suggests that such a sine model is not a terrible misspecification and assigns an even higher posterior probability of 20% to the possibility that the amplitude is less than 0.1 ppbv.
For this reason one would hope that once more data becomes available it can be compared against the trend shown here and the conclusions updated through the Science publication platform if negative.

Variation of atmospheric methane concentration on Mars
Svatopluk Civis
  • researcher
  • J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, CZ18223 Prague 8, Czech Republic.
Antonin Knizek
  • PhD student
  • J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, CZ18223 Prague 8, Czech Republic.

In the issue of Science published on 8 June 2018, a team of scientists from NASA responsible for the Curiosity rover management published an article titled: "Background levels of methane in Mars' atmosphere show strong seasonal variation'(1). The article presents a detailed analysis of the past 5 years worth of measurement by Curiosity and concludes that strong seasonal fluctuation of methane concentration exists on Mars. In the Supplementary Information, the authors compare the results in terms of temperature, UV irradiation, atmospheric pressure throughout the Martian year.
The authors state that: 'Existing models including atmospheric transport and circulation are unable to reproduce the reported high concentrations of methane and its spatial and temporal variability, even when including possible clathrate release, surface/regolith adsorption/desoption, seasonally variable production from UV breakdown of surface organics, or proposed mechanisms of rapid loss.' The authors neglected to mention a viable abiotic explanation of the seasonal methane emission that we proposed in (2). Encouragingly, the predictions we made in that paper happen to fit very well to the new data. In our scenario, methane is a product of a photocatalytic reduction of CO2, the main constituent of the Martian atmosphere. We compared the production rates of methane to other conditions on Mars, namely water atmospheric content, atmospheric pressure and UV irradiation.
Back then, of course, the data from the last 5 years were not published and we had only a few data points from Curiosity, which were published in 2015(3). Based on these data and our model, we predicted that there would be variation of methane on Mars and explained its source. In search for more data to support the prediction, we even asked several of the authors of the now-published article for more data from Curiosity. Since the authors did not share their data with us, we weren't able to refine our model, so it is fairly impressive that it now fits the data so well.
In light of this newly published data, we would like to remind the community that there already exists a theory which successfully predicted and attempted to explain the seasonal variation 9 months ago(3).
1. C. R. Webster et al., Background levels of methane in Mars{\textquoteright} atmosphere show strong seasonal variations. Science (80-. ). 360, 1093–1096 (2018).
2. S. Civiš et al., Origin of methane and biomolecules from a CO2 cycle on terrestrial planets. Nat. Astron. 1, 721–726 (2017).
3. C. R. Webster et al., Mars methane detection and variability at Gale crater. Science (80-. ). 347, 415–417 (2015).

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