Source: https://www.nature.com/articles/s41561-019-0331-9?error=cookies_not_supported&code=52877580-bfc2-4482-bc42-7f60cb194de8
Timestamp: 2019-04-19 21:18:58+00:00

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Reports of methane detection in the Martian atmosphere have been intensely debated. The presence of methane could enhance habitability and may even be a signature of life. However, no detection has been confirmed with independent measurements. Here, we report a firm detection of 15.5 ± 2.5 ppb by volume of methane in the Martian atmosphere above Gale Crater on 16 June 2013, by the Planetary Fourier Spectrometer onboard Mars Express, one day after the in situ observation of a methane spike by the Curiosity rover. Methane was not detected in other orbital passages. The detection uses improved observational geometry, as well as more sophisticated data treatment and analysis, and constitutes a contemporaneous, independent detection of methane. We perform ensemble simulations of the Martian atmosphere, using stochastic gas release scenarios to identify a potential source region east of Gale Crater. Our independent geological analysis also points to a source in this region, where faults of Aeolis Mensae may extend into proposed shallow ice of the Medusae Fossae Formation and episodically release gas trapped below or within the ice. Our identification of a probable release location will provide focus for future investigations into the origin of methane on Mars.
The PFS data used in this study are publicly available via the ESA Planetary Science Archive. References of terrestrial gas seepage data are reported in the Supplementary Information. Data used to map water-equivalent hydrogen are available from J. T. Wilson (Johns Hopkins University Applied Physics Laboratory, Jack.Wilson@jhuapl.edu). All other geological data of Mars used in this study are in the public domain and include published papers, data provided in the US Geological Survey Mars Global GIS version 2.1 (which can be accessed on the Mars GIS FTP site: ftp://pdsimage2.wr.usgs.gov/pub/pigpen/mars/Global_GIS_Mars/; file name: MarsGIS_Equi0_v21.zip (note that v21 is used in the file name for v2.1)), and Context Camera and Visible data image mosaics provided by Google Earth (Mars).
The core GEM model used for this work is publicly available through http://collaboration.cmc.ec.gc.ca/science/rpn.comm/. The routines that were modified for the application to Mars are explained in ref. 39 and available upon request from F.D. (Frank.Daerden@aeronomie.be) and L.N. (Lori.Neary@aeronomie.be). The model output used in this paper is available upon request from F.D., L.N. and S.V. (Sebastien.Viscardy@aeronomie.be). The equations for the statistical analysis are included in the Methods. The computer code to reproduce the results is available from S.V.
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We thank Environment and Climate Change Canada for providing the GEM model for research purposes, and for support. We thank J. T. Wilson for providing the data used to map the water-equivalent hydrogen from improved-resolution Mars Odyssey Neutron Spectrometer data. We thank O. Witasse, D. Titov, P. Martin and the ESA Science Ground Segment and Flight Control teams for successful operation of the MEx mission over more than a decade. The PFS experiment was built at the Institute for Space Astrophysics and Planetology (formerly the Institute for Interplanetary Space Physics) of the National Institute for Astrophysics, and is currently funded by the Italian Space Agency (agreement number 2018-2-HH.0) in the context of the science activities for the Nadir and Occultation for Mars Discovery spectrometer and the Atmospheric Chemistry Suite onboard the Trace Gas Orbiter ExoMars 2016, and for PFS-MEx. D.O. is supported by the Planetary Science Institute. S.V. and L.N. are supported by the ESA PRODEX Office (contract number Prodex_NOMADMarsScience_C4000121493_2017-2019). S.V. is also supported by the ‘Excellence of Science’ project ‘Evolution and Tracers of Habitability on Mars and the Earth’ (FNRS 30442502). P.W. is supported by the ‘UPWARDS’ project, funded from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 633127. S.A. has been supported by the FNRS ‘CRAMIC’ project under grant agreement number T.0171.16. This paper is dedicated to our colleague, V. Formisano, who recently passed away.
M.G. and S.A. developed the new approach to PFS data selection and treatment. M.G. performed the CH4 retrieval. A.A., P.W. and S.A. supervised the PFS science operations, planning, commanding and data archiving. A.C.-M. provided ancillary data and other geometrically relevant models for PFS and MEx through the SPICE software suite. A.C.-M., J.M.-Y.l.P. and D.M. contributed to planning the PFS observations and successful implementation and execution of the PFS spot-tracking observations. V.F. developed the concept and was the former principal investigator for PFS-MEx. S.V., F.D. and L.N. developed and performed the GCM simulations and analysis. G.E. and D.O. performed the geological analysis and evaluation of terrestrial seepage patterns. M.A. was responsible for the PFS-MEx project from the Italian Space Agency side. All authors contributed to interpretation of the results and preparation of the manuscript.

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