Low Hesperian P_(CO2) constrained from in situ mineralogical analysis at Gale Crater, Mars

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Bristow, Thomas F., Haberle, Robert M., Blake, David F., Des Marais, David J., Eigenbrode, Jennifer L., Fairén, Alberto G., Grotzinger, John P., Stack, Kathryn M., Mischna, Michael A., Rampe, Elizabeth B., Siebach, Kirsten L., Sutter, Brad, Vaniman, David T., Vasavada, Ashwin R.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: National Academy of Sciences 2017
• Subjects: Hesperian Mars; martian atmosphere; Mars Science Laboratory; Gale Crater; carbon dioxide; Sadler; Yellowknife; Yellowknife Bay
• Online Access: https://doi.org/10.1073/pnas.1616649114; https://www.ncbi.nlm.nih.gov/pmc/PMC5338541

Carbon dioxide is an essential atmospheric component in martian climate models that attempt to reconcile a faint young sun with planetwide evidence of liquid water in the Noachian and Early Hesperian. In this study, we use mineral and contextual sedimentary environmental data measured by the Mars Science Laboratory (MSL) Rover Curiosity to estimate the atmospheric partial pressure of CO_2 (P_(CO2)) coinciding with a long-lived lake system in Gale Crater at ∼3.5 Ga. A reaction–transport model that simulates mineralogy observed within the Sheepbed member at Yellowknife Bay (YKB), by coupling mineral equilibria with carbonate precipitation kinetics and rates of sedimentation, indicates atmospheric P_(CO2) levels in the 10s mbar range. At such low P_(CO2) levels, existing climate models are unable to warm Hesperian Mars anywhere near the freezing point of water, and other gases are required to raise atmospheric pressure to prevent lake waters from being lost to the atmosphere. Thus, either lacustrine features of Gale formed in a cold environment by a mechanism yet to be determined, or the climate models still lack an essential component that would serve to elevate surface temperatures, at least locally, on Hesperian Mars. Our results also impose restrictions on the potential role of atmospheric CO_2 in inferred warmer conditions and valley network formation of the late Noachian. © 2017 National Academy of Sciences. Freely available online through the PNAS open access option. Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved December 27, 2016 (received for review October 6, 2016). Published ahead of print February 6, 2017. We acknowledge the support of the Jet Propulsion Lab engineering and MSL operations staff. Thanks to K. Zahnle, E. Kite, and M. Daswani for discussions, and constructive reviews from I. Halevy, J. Kasting, P. Niles, and two anonymous reviewers on this and a previous version of the manuscript. We thank P. Sadler for advice and access to sedimentation ...