Organic compounds in the Tarda C2 ungrouped carbonaceous chondrite: Evaluating the sources of contamination in a desert fall

Abstract

Studying organic compounds in meteorites provides important insight into the chemical processes that occurred in the early solar system. Once meteorites reach the Earth's surface, they are subject to terrestrial organic contamination that may confound the conclusions that we draw from meteorite organic analyses. Within this study, specimens of the Tarda C2 ungrouped carbonaceous chondrite, collected within a few days of its fall on August 25, 2020, from a barren desert in Morocco, were analyzed for their organic compound contents. In addition, a sand sample from the strewn field was analyzed to confirm the sources of a handful of contaminating compounds detected in the Tarda stones. Using dichloromethane (DCM) rinses of the Tarda stone exteriors and DCM and hot water extractions of meteorite specimen powders and sand sample, and analysis of the soluble organics by gas chromatography-mass spectrometry, we distinguish between extraterrestrial and contaminant sources for each organic compound. In this study, N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) was used to derivatize the hot water extractions to utilize its single-step derivatization reaction ability. The compounds determined to be intrinsic to Tarda include propanoic acid, propanedioic acid, butanedioic acid, fumaric acid, methylmaleic acid, threonine, proline, glycine, urea, and cyclic octaatomic sulfur. We detected numerous terrestrial organic compounds, all of which were traced back to the meteorites' collection area, with several being confirmed in the sand sample. Our results have implications for best practices for the collection of freshly fallen meteorites, especially carbonaceous chondrites, as well as how specimens should be handled and curated after collection.

Testing materials to mitigate terrestrial organic contamination of meteorites: Implications for collection, curation, and handling of astromaterials

“…Combining results from this study with previous studies of soluble organic analyses on meteorites (Lee et al., 2021; Tunney et al., 2020; Tunney, Hill, Herd, & Hilts, 2022; Tunney, Hill, Herd, Hilts, et al., 2022), as well as previous considerations for curation of astromaterials (Calaway et al., 2014), we have developed 16 key recommendations for recovering, handling, and curating freshly fallen meteorites: Meteorite specimens should be collected as rapidly as possible in order to avoid unwanted chemical or physical modifications (e.g., weathering) and accumulation of contaminants (either chemical or biological). Although terrestrial contamination is essentially instantaneous once within the Earth's atmosphere, accumulation of organics can be prevented, particularly with microbial communities that colonize samples at a lower rate (Lee et al., 2021).…”

“…The presence of life and other processes at the Earth's surface can destroy, alter, or contaminate a meteorite's intrinsic properties and replace them with terrestrial signatures. Terrestrial organic compounds have been shown to rapidly, and potentially in most cases, extensively contaminate meteorites with a range of compounds from primarily agricultural products, fuels, pharmaceuticals, and plastics (e.g., Botta et al., 2010; Elsila et al., 2016; Glavin et al., 2010; Martins, 2019; Sephton, 2002; Steele et al., 2000; Tunney et al., 2020; Tunney, Hill, Herd, & Hilts, 2022; Tunney, Hill, Herd, Hilts, et al., 2022). Although terrestrial contamination has become increasingly documented, few studies examining contamination resulting from recovery and curation have been carried out thus far.…”

Insoluble macromolecular organic matter in the Winchcombe meteorite

“…Semivolatiles are typically are in the diesel range of hydrocarbons (C 10‐20 ) and include terpenoids that are produced by plants and are used in fragrances and cleaning products (e.g., Watson et al., 2003). There are a number of studies that have looked at common contaminants in the organic analysis of geological and meteorite samples that cover this subject in much greater detail (e.g., Brocks et al., 2008; George et al., 2010; Greenwood et al., 2009; Herd et al., 2016; Illing et al., 2014; Tunney et al., 2022).…”

The amino acid and polycyclic aromatic hydrocarbon compositions of the promptly recovered CM2 Winchcombe carbonaceous chondrite

“…However, not all CM falls were investigated using compound targeted analysis, as such an approach requires a substantial mass of samples for the effective detection of the containing SOM species, while some meteorite falls such as Maribo were recovered below such limits (only ~30 g of specimens recovered). The condition of the meteorite fall site also played a role; for example, Maribo was intensely rained on before collection, which hampered the SOM inventory (Haack et al., 2012), whereas Tarda was collected from a barren hot desert in Morocco and thus not as extensively influenced by terrestrial water as Maribo (Tunney et al., 2022).…”