Depleted carbon isotope compositions observed at Gale crater, Mars

Christopher H House; Gregory M Wong; Christopher R Webster; Gregory J Flesch; Heather B Franz; Jennifer C Stern; Alex Pavlov; Sushil K Atreya; Jennifer L Eigenbrode; Alexis Gilbert; Amy E Hofmann; Maëva Millan; Andrew Steele; Daniel P Glavin; Charles A Malespin; Paul R Mahaffy

doi:10.1073/pnas.2115651119

Depleted carbon isotope compositions observed at Gale crater, Mars

Proc Natl Acad Sci U S A. 2022 Jan 25;119(4):e2115651119. doi: 10.1073/pnas.2115651119.

Authors

Christopher H House^{1

2}, Gregory M Wong³, Christopher R Webster⁴, Gregory J Flesch⁴, Heather B Franz⁵, Jennifer C Stern⁵, Alex Pavlov⁵, Sushil K Atreya⁶, Jennifer L Eigenbrode⁵, Alexis Gilbert⁷, Amy E Hofmann⁴, Maëva Millan^{5

8}, Andrew Steele⁹, Daniel P Glavin⁵, Charles A Malespin⁵, Paul R Mahaffy⁵

Affiliations

¹ Department of Geosciences, The Pennsylvania State University, University Park, PA 16802; chrishouse@psu.edu.
² Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, PA 16802.
³ Department of Geosciences, The Pennsylvania State University, University Park, PA 16802.
⁴ NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109.
⁵ Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771.
⁶ Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109.
⁷ Department of Earth and Planetary Sciences and Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan.
⁸ Department of Biology, Georgetown University, Washington, DC 20057.
⁹ Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015.

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 (δ¹³C_VPDB) 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.

Keywords: Gale crater; Mars; carbon isotopes; methane; pyrolysis.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.