Combustion of organic matter in Mars analogs using SAM-like techniques
Abstract
The combustion experiment on the Sample Analysis at Mars (SAM) suite on Curiosity will heat a sample of Mars regolith in the presence of oxygen and measure the carbon isotopic composition (δ13C) of the evolved CO2 using the Tunable Laser Spectrometer (TLS). The degree to which the δ13C of the sample is representative of any organic carbon present depends on a) whether complete combustion has been achieved, and b) the simultaneous presence of inorganic, or mineralogical carbon in the sample, and our ability to quantify its contribution to the bulk δ13C. To optimize and characterize combustion of a variety of organic molecules in a range of rock matrices, combustion experiments simulating those to be performed on SAM were conducted at NASA Goddard. CO2 gas generated by heating Mars analogs in a SAM-like oven in the presence of oxygen on a laboratory breadboard was captured and analyzed via IRMS for δ13C. These values were compared to bulk and total organic carbon (TOC) abundance and δ13C values using commercial flash combustion EA- IRMS techniques to determine whether quantitative conversion of reduced carbon to CO2 was achieved. Factors contributing to incomplete combustion and isotopic fractionation include structural complexity of reduced organics, their thermal decomposition temperatures, and mineral-organic associations. An additional consideration must be made for unintentional combustion by oxidizing salts (perchlorates), which may partially or totally oxidize reduced organic compounds to CO2, depending on soil perchlorate concentration, sample matrix, and how refractory the organics are. Thus, to investigate the oxidizing potential of a salt known to exist on the Martian surface, laboratory breadboard experiments heating simple and complex organics in the presence of Mg perchlorate were performed using a SAM-like oven coupled to a Hiden Mass Spectrometer and gas collection manifold. Samples were heated in the absence and presence of Mg perchlorate to ~900 °C and mass spectral data were monitored for O2, CO2, CO, and chlorinated hydrocarbons. If CO2 was produced by perchlorate-induced oxidation of organics, a second experiment was conducted and CO2 was captured for δ13C analysis. These results could help determine whether δ13C of CO2 evolved during decomposition of organics could provide useful information in lieu of the organics themselves, in the case of the coexistence of organics with highly oxidizing materials in the regolith.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.P13A1887S
- Keywords:
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- 1041 GEOCHEMISTRY / Stable isotope geochemistry;
- 1060 GEOCHEMISTRY / Planetary geochemistry;
- 5494 PLANETARY SCIENCES: SOLID SURFACE PLANETS / Instruments and techniques;
- 6225 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS / Mars