Depleted carbon isotope compositions observed at Gale crater, Mars
Abstract
Obtaining carbon isotopic information for organic carbon from Martian sediments has long been a goal of planetary science, as it has the potential to elucidate the origin of such carbon and aspects of Martian carbon cycling. Carbon isotopic values (δ¹³CVPDB) of the methane released during pyrolysis of 24 powder samples at Gale crater, Mars, show a high degree of variation (−137 ± 8‰ to +22 ± 10‰) when measured by the tunable laser spectrometer portion of the Sample Analysis at Mars instrument suite during evolved gas analysis. Included in these data are 10 measured δ¹³C values less than −70‰ found for six different sampling locations, all potentially associated with a possible paleosurface. There are multiple plausible explanations for the anomalously depleted ¹³C observed in evolved methane, but no single explanation can be accepted without further research. Three possible explanations are the photolysis of biological methane released from the subsurface, photoreduction of atmospheric CO₂, and deposition of cosmic dust during passage through a galactic molecular cloud. All three of these scenarios are unconventional, unlike processes common on Earth.
Additional Information
© 2022 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY). Edited by Mark Thiemens, Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA; received August 26, 2021; accepted December 1, 2021. We thank the MSL, Mastcam, and SAM teams for their dedicated work operating the mission, crafting and sequencing scripts that are sent to the Curiosity rover and the SAM instrument to make these measurements possible, and their support in data collection, analyses, and discussions. We also acknowledge the NASA Mars Exploration Program for providing support through the MSL Participating Scientist Program (C.H.H., J.L.E., M.M.), and the NASA Earth and Space Science Fellowship and NASA Space Grant Programs for participant support (G.M.W.). Additionally, the NASA Astrobiology Center for Isotopologue Research project facilitated the collaboration involving intramolecular isotopes (A.G.). We also thank Dr. Richard Becker for useful discussions, Dr. Todd Sowers and Zhidan Zhang for assistance with laboratory experiments, and two anonymous reviewers for their comments and excellent suggestions. Data Availability: All MSL SAM data are available at the Geosciences Node of NASA's Planetary Data System (https://pds-geosciences.wustl.edu/missions/msl/sam.htm). All study data are included in the article and/or SI Appendix. Author contributions: C.R.W. and P.R.M. designed research; C.H.H., G.M.W., C.R.W., G.J.F., H.B.F., and J.C.S. performed research; C.H.H., G.M.W., C.R.W., G.J.F., H.B.F., J.C.S., A.P., S.K.A., J.L.E., A.G., A.E.H., M.M., A.S., D.P.G., C.A.M., and P.R.M. analyzed data; C.H.H. performed laboratory pyrolysis experiments; C.H.H. and G.M.W. wrote the paper with contributions from all authors; C.R.W. wrote method description for the tunable laser spectrometer data analyses; G.M.W. calculated sulfur isotopes and analyzed EGA profiles; C.R.W. and G.J.F. developed and implemented methods for calculating the methane isotopic composition from MSL-TLS spectra; H.B.F. calculated BSW abundances from EGA profiles and calculated sulfur isotopes; A.P. contributed to the concept of interplanetary dust as an explanation of results; S.K.A. contributed to the concept of the photochemical explanations of the results; H.B.F., J.C.S., and J.L.E. contributed to numerous discussions of results and the development of explanations for the results; A.G. and A.E.H. contributed new reagents/analytic tools; and C.A.M. and P.R.M. led discussions for instrument team for this work. The authors declare no competing interest. This article is a PNAS Direct Submission. This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2115651119/-/DCSupplemental.Attached Files
Published - e2115651119.full.pdf
Supplemental Material - pnas.2115651119.sapp.pdf
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Additional details
- Eprint ID
- 112974
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- CaltechAUTHORS:20220119-460984800
- NASA Earth and Space Science Fellowship
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2022-01-19Created from EPrint's datestamp field
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2022-07-25Created from EPrint's last_modified field