Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars

Creators: Eigenbrode, Jennifer L.; Summons, Roger E.; Steele, Andrew; Freissinet, Caroline; Millan, Maëva; Navarro-González, Rafael; Sutter, Brad; McAdam, Amy C.; Franz, Heather B.; Glavin, Daniel P.; Archer, Paul D., Jr.; Mahaffy, Paul R.; Conrad, Pamela G.; Hurowitz, Joel A.; Grotzinger, John P.; Gupta, Sanjeev; Ming, Doug W.; Sumner, Dawn Y.; Szopa, Cyril; Malespin, Charles; Buch, Arnaud; Coll, Patrice

Abstract

Establishing the presence and state of organic matter, including its possible biosignatures, in martian materials has been an elusive quest, despite limited reports of the existence of organic matter on Mars. We report the in situ detection of organic matter preserved in lacustrine mudstones at the base of the ~3.5-billion-year-old Murray formation at Pahrump Hills, Gale crater, by the Sample Analysis at Mars instrument suite onboard the Curiosity rover. Diverse pyrolysis products, including thiophenic, aromatic, and aliphatic compounds released at high temperatures (500° to 820°C), were directly detected by evolved gas analysis. Thiophenes were also observed by gas chromatography–mass spectrometry. Their presence suggests that sulfurization aided organic matter preservation. At least 50 nanomoles of organic carbon persists, probably as macromolecules containing 5% carbon as organic sulfur molecules.

Additional Information

© 2018 American Association for the Advancement of Science. Received 4 January 2018; accepted 29 March 2018. We thank reviewers for their constructive comments, the MSL and SAM teams for successful operations of SAM on Mars and thoughtful science discussions, and K. Irikura for calculating ionization cross sections. This work was funded by NASA's Mars Exploration Program. NASA's MSL Participating Scientist program supported J.L.E., R.E.S., and D.P.G. for this effort. S.G. acknowledges funding from the UK Space Agency. R.N.-G. was funded by the Universidad Nacional Autónoma de México and the Consejo Nacional de Ciencia y Tecnología de México. Author contributions: J.L.E. developed data processing methods, calculated and interpreted EGA data, and wrote most of the manuscript and supplementary materials. R.E.S, A.S, B.S., and P.R.M. wrote sections of text on pyrolysis, meteorites, geological context, and methods, respectively. C.F., M.M., D.P.G., A.S., and C.S. calculated and interpreted GC-MS data. M.M. performed SAM GC breadboard tests. H.B.F., P.D.A., and B.S. contributed to analysis of EGA data. R.N-G. performed laboratory analyses necessary to understand the SAM background. All authors participated in data acquisition, discussion of results, and/or editing of the manuscript. The authors declare no competing financial interests. Data and materials availability: Reduced data records (RDRs) from SAM flight experiments are archived in the Planetary Data System (https://pds.nasa.gov) and are identifiable by the sol or test identification (TID) numbers listed in table S6. All processed data are available in the text or the supplementary materials.

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