Carbon, Carbides, and Methane in an Apollo 12 Sample

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Abstract
Total carbon in the Apollo 12 sample 12023 fines was 110 micrograms per gram of sample with a carbon isotopic abundance δ 13 C (relative to the Pee Dee belemnite standard) of +12 per mil. Hydrolysis of the fines with deuterium chloride yielded undeuterated methane along with deuterated hydrocarbons, thus confirming the presence of 7 to 21 micrograms of carbon per gram of sample as carbide and about 2 micrograms of carbon per gram of sample as indigenous methane. After vacuum pyrolysis of the fines to 1100°C the following gases were detected in the relative abundance: carbon monoxide ⪢ carbon dioxide > methane. Variations of the δ 13 C value with the pyrolysis temperature indicated the presence of carbon with more than one range of isotopic values. The observed δ 13 C value of +14 per mil for lunar carbide is much higher than that of carbide in meteorites. These results suggest that lunar carbide is either indigenous to the moon or a meteoritic contribution that has been highly fractionated isotopically.