Depleted carbon isotope compositions observed at Gale crater, Mars

House, Christopher H.; Wong, G. M.; Webster, Christopher R.; Flesch, Gregory J.; Franz, H. B.; Stern, J. C.; Pavlov, Alexander A.; Atreya, S. K.; Eigenbrode, J. L.; Gilbert, Alexis; Hofmann, Amy E.; Millan, Maëva; Steele, A.; Glavin, Daniel P.; Malespin, C. A.; Mahaffy, P. R.

doi:10.1073/pnas.2115651119

Cited by 56 publications

(82 citation statements)

References 76 publications

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“…The source of the organic carbon evolving high-temperature CO 2 during combustion is not easily resolved. Our δ 13 C values for combusted CO 2 (δ 13 C = −10.1‰ to −32.9‰) do not show the same extreme 13 C depletions as recently reported δ 13 C values for CH 4 evolved during SAM EGA pyrolysis experiments (−96‰ to −71‰) on the same CB samples ( 37 ). This is likely because δ 13 C of combusted CO 2 is a bulk measurement of all carbon in the sample, and CH 4 only represents a very small portion (∼0.2‰) of the total carbon in the sample.…”

Section: Discussionsupporting

confidence: 72%

Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars

Stern

Malespin

Eigenbrode

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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The Sample Analysis at Mars instrument stepped combustion experiment on a Yellowknife Bay mudstone at Gale crater, Mars revealed the presence of organic carbon of Martian and meteoritic origins. The combustion experiment was designed to access refractory organic carbon in Mars surface sediments by heating samples in the presence of oxygen to combust carbon to CO 2 . Four steps were performed, two at low temperatures (less than ∼550 °C) and two at high temperatures (up to ∼870 °C). More than 950 μg C/g was released at low temperatures (with an isotopic composition of δ 13 C = +1.5 ± 3.8‰) representing a minimum of 431 μg C/g indigenous organic and inorganic Martian carbon components. Above 550 °C, 273 ± 30 μg C/g was evolved as CO 2 and CO (with estimated δ 13 C = −32.9‰ to −10.1‰ for organic carbon). The source of high temperature organic carbon cannot be definitively confirmed by isotopic composition, which is consistent with macromolecular organic carbon of igneous origin, meteoritic infall, or diagenetically altered biomass, or a combination of these. If from allochthonous deposition, organic carbon could have supported both prebiotic organic chemistry and heterotrophic metabolism at Gale crater, Mars, at ∼3.5 Ga.

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Section: Discussionsupporting

confidence: 72%

Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars

Stern

Malespin

Eigenbrode

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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“… 2017b ) and 13 C (House et al. 2022 ). In all cases, non-biological explanations are available, and furthermore, the understanding of martian geochemical and isotopic processes is limited.…”

Section: Assessment Of Habitabilitymentioning

confidence: 99%

Mission Overview and Scientific Contributions from the Mars Science Laboratory Curiosity Rover After Eight Years of Surface Operations

Vasavada

2022

Space Sci Rev

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NASA’s Mars Science Laboratory mission, with its Curiosity rover, has been exploring Gale crater (5.4° S, 137.8° E) since 2012 with the goal of assessing the potential of Mars to support life. The mission has compiled compelling evidence that the crater basin accumulated sediment transported by marginal rivers into lakes that likely persisted for millions of years approximately 3.6 Ga ago in the early Hesperian. Geochemical and mineralogical assessments indicate that environmental conditions within this timeframe would have been suitable for sustaining life, if it ever were present. Fluids simultaneously circulated in the subsurface and likely existed through the dry phases of lake bed exposure and aeolian deposition, conceivably creating a continuously habitable subsurface environment that persisted to less than 3 Ga in the early Amazonian. A diversity of organic molecules has been preserved, though degraded, with evidence for more complex precursors. Solid samples show highly variable isotopic abundances of sulfur, chlorine, and carbon. In situ studies of modern wind-driven sediment transport and multiple large and active aeolian deposits have led to advances in understanding bedform development and the initiation of saltation. Investigation of the modern atmosphere and environment has improved constraints on the timing and magnitude of atmospheric loss, revealed the presence of methane and the crater’s influence on local meteorology, and provided measurements of high-energy radiation at Mars’ surface in preparation for future crewed missions. Rover systems and science instruments remain capable of addressing all key scientific objectives. Emphases on advance planning, flexibility, operations support work, and team culture have allowed the mission team to maintain a high level of productivity in spite of declining rover power and funding.

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“…In the case of a collision between CH 3 radicals, the kinetic isotope effects are calculated to be k’ / k = 0.9842 and k” / k = 0.9682, where the prime and double prime refers to singly and doubly substituted isotopologues, respectively. If kinetic isotope effects follow a stochastic distribution, ( k” / k )/( k’ / k ) 2 must be equal to 1 (see Supplementary Note 1 ). Any deviation from unity leads to Δ 13 C 13 C values different from 0.…”

Section: Resultsmentioning

confidence: 99%

“…The 13 C- 13 C signature may thus be applied in investigations of the origin of ethane in terrestrial and extra-terrestrial settings. Moreover, not only ethane but a variety of organic molecules containing C-C bonds can be subjected to this analytical approach to distinguish abiotic formation pathways, in geological and even extra-terrestrial settings, such as Mars, Titan, and Enceladaus 2 , 5 , 42 .…”

Section: Resultsmentioning

confidence: 99%

Low 13C-13C abundances in abiotic ethane

et al. 2022

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Distinguishing biotic compounds from abiotic ones is important in resource geology, biogeochemistry, and the search for life in the universe. Stable isotopes have traditionally been used to discriminate the origins of organic materials, with particular focus on hydrocarbons. However, despite extensive efforts, unequivocal distinction of abiotic hydrocarbons remains challenging. Recent development of clumped-isotope analysis provides more robust information because it is independent of the stable isotopic composition of the starting material. Here, we report data from a 13C-13C clumped-isotope analysis of ethane and demonstrate that the abiotically-synthesized ethane shows distinctively low 13C-13C abundances compared to thermogenic ethane. A collision frequency model predicts the observed low 13C-13C abundances (anti-clumping) in ethane produced from methyl radical recombination. In contrast, thermogenic ethane presumably exhibits near stochastic 13C-13C distribution inherited from the biological precursor, which undergoes C-C bond cleavage/recombination during metabolism. Further, we find an exceptionally high 13C-13C signature in ethane remaining after microbial oxidation. In summary, the approach distinguishes between thermogenic, microbially altered, and abiotic hydrocarbons. The 13C-13C signature can provide an important step forward for discrimination of the origin of organic molecules on Earth and in extra-terrestrial environments.

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Depleted carbon isotope compositions observed at Gale crater, Mars

Cited by 56 publications

References 76 publications

Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars

Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars

Mission Overview and Scientific Contributions from the Mars Science Laboratory Curiosity Rover After Eight Years of Surface Operations

Low 13C-13C abundances in abiotic ethane

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