![]() ![]() During EGA, organic material can produce a range of products including CO 2, CH 4, CO, OCS, CS 2, and molecular organic fragments. The redox state of the oven, in practice, depends on the relative abundances of oxychlorine species and reduced minerals in each sample. A fraction of the evolved gas mixture is directly analyzed with a quadrupole mass spectrometer, and a specific preselected temperature cut of the remaining gas is diverted to the Herriott cell of the TLS. Methane abundances and δ 13C values were determined from analyzing TLS-SAM high-resolution spectra.įor evolved gas analysis (EGA) at Gale crater, drilled powder or scooped fines are heated at 35 ☌ min −1 under a helium flow in quartz cups up to ∼850 ☌. This study considered the carbon isotopic values of methane evolved during pyrolysis as observed by the MSL tunable laser spectrometer (TLS) of the Sample Analysis at Mars (SAM) instrument suite ( 3) from 24 samples from Gale crater, Mars. Methods used in this work are also described in the supplement to this manuscript. A description of the mission samples studied can be found in the supplement, and a stratigraphic column is shown in Fig. These samples have been collected from varied lithologies from hundreds of meters of stratigraphy in Gale crater that represent the complex history and evolution of the region. MSL has collected and analyzed more than 30 drilled samples on Mars between August 2012 and July 2021. Extended exploration by the Mars Science Laboratory (MSL) Curiosity rover of the fluvio-lacustrine sedimentary system at Gale crater provides unique opportunities, as samples are collected from a variety of locations within a known stratigraphic context ( 1, 2). All three of these scenarios are unconventional, unlike processes common on Earth.Ĭarbon isotopic data from Martian sedimentary organic carbon can potentially elucidate the origin of indigenous organics and reveal aspects of the Martian carbon cycle. Three possible explanations are the photolysis of biological methane released from the subsurface, photoreduction of atmospheric CO 2, and deposition of cosmic dust during passage through a galactic molecular cloud. There are multiple plausible explanations for the anomalously depleted 13C observed in evolved methane, but no single explanation can be accepted without further research. Included in these data are 10 measured δ 13C values less than −70‰ found for six different sampling locations, all potentially associated with a possible paleosurface. Carbon isotopic values (δ 13C 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. 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.
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