New insights into the heterogeneity of the Tagish Lake meteorite: Soluble organic compositions of variously altered specimens

Abstract

The Tagish Lake carbonaceous chondrite exhibits a unique compositional heterogeneity that may be attributed to varying degrees of aqueous alteration within the parent body asteroid. Previous analyses of soluble organic compounds from four Tagish Lake meteorite specimens (TL5b, TL11h, TL11i, TL11v) identified distinct distributions and isotopic compositions that appeared to be linked to their degree of parent body processing (Herd et al. 2011; Glavin et al. 2012; Hilts et al. 2014). In the present study, we build upon these initial observations and evaluate the molecular distribution of amino acids, aldehydes and ketones, monocarboxylic acids, and aliphatic and aromatic hydrocarbons, including compound‐specific δ13C compositions, for three additional Tagish Lake specimens: TL1, TL4, and TL10a. TL1 contains relatively high abundances of soluble organics and appears to be a moderately altered specimen, similar to the previously analyzed TL5b and TL11h lithologies. In contrast, specimens TL4 and TL10a both contain relatively low abundances of all of the soluble organic compound classes measured, similar to TL11i and TL11v. The organic‐depleted composition of TL4 appears to have resulted from a relatively low degree of parent body aqueous alteration. In the case of TL10a, some unusual properties (e.g., the lack of detection of intrinsic monocarboxylic acids and aliphatic and aromatic hydrocarbons) suggest that it has experienced extensive alteration and/or a distinct organic‐depleted alteration history. Collectively, these varying compositions provide valuable new insights into the relationships between asteroidal aqueous alteration and the synthesis and preservation of soluble organic compounds.

Extraterrestrial organic compounds and cyanide in the CM2 carbonaceous chondrites Aguas Zarcas and Murchison

“…The use of lower amounts of extracted sample hampered our ability to screen the full molecular diversity of carbonyl compounds in Aguas Zarcas and Murchison. Based on our previous experiences analyzing meteoritic carbonyl compounds (Simkus et al 2019b(Simkus et al , 2019c, if larger meteorite samples would have been extracted, additional carbonyl compounds present in relatively low abundances would have been detectable above background levels; as the background levels would have likely remained the same as the present study given that the analytical protocol would have remained unchanged. Formaldehyde is the most abundant aldehyde in Aguas Zarcas, making up~88% of the aldehyde content, while acetaldehyde is the most abundant aldehyde in Murchison, comprising~45% of the aldehyde (Table 1).…”

“…Triplicate injections of derivatives were made in split mode (split flow: 5 mL min À1 , held for 1 min) in aliquots of 1 µL. The mass spectra were used to identify and quantify the meteoritic carbonyl compounds and carboxylic acids by comparison to reference standards and application of calibration curves as described elsewhere (Aponte et al 2019;Simkus et al 2019bSimkus et al , 2019c.…”

Organic contamination on the surface of meteorites as a function of space and time: A case study of the Buzzard Coulee H4 chondrite

“…The instrument method for the GC‐MS analysis is similar to those described by Simkus et al. (2019) and is as follows. The gas chromatography separation was executed at the University of Alberta on an Agilent 5975C using a HP‐5MS column (30 m length, 0.25 µm film thickness, 250 µm internal diameter), with detection being performed using an Agilent 5975C mass selective detector (MSD).…”

Methodologies for Analyzing Soluble Organic Compounds in Extraterrestrial Samples: Amino Acids, Amines, Monocarboxylic Acids, Aldehydes, and Ketones

“…Meteoritic monocarboxylic acids are most often analyzed via GC-MS as underivatized compounds, either through direct solvent injection [74,76,115,117,118] or using SPME [70,75,77,78,80,119,120] (Table 3). Avoiding sample derivatization decreases sample processing time, minimizes sample transfer steps which may otherwise result in partial loss of relatively volatile acids, and reduces the risk of introducing contamination.…”