The amino acid composition of the Sutter's Mill CM2 carbonaceous chondrite

Abstract

Abstract-We determined the abundances and enantiomeric compositions of amino acids in Sutter's Mill fragment #2 (designated SM2) recovered prior to heavy rains that fell April 25-26, 2012, and two other meteorite fragments, SM12 and SM51, that were recovered postrain. We also determined the abundance, enantiomeric, and isotopic compositions of amino acids in soil from the recovery site of fragment SM51. The three meteorite stones experienced terrestrial amino acid contamination, as evidenced by the low D/L ratios of several proteinogenic amino acids. The D/L ratios were higher in SM2 than in SM12 and SM51, consistent with rain introducing additional L-amino acid contaminants to SM12 and SM51. Higher percentages of glycine, b-alanine, and c-amino-n-butyric acid were observed in free form in SM2 and SM51 compared with the soil, suggesting that these free amino acids may be indigenous. Trace levels of D+L-b-aminoisobutyric acid (b-AIB) observed in all three meteorites are not easily explained as terrestrial contamination, as b-AIB is rare on Earth and was not detected in the soil. Bulk carbon and nitrogen and isotopic ratios of the SM samples and the soil also indicate terrestrial contamination, as does compound-specific isotopic analysis of the amino acids in the soil. The amino acid abundances in SM2, the most pristine SM meteorite analyzed here, are approximately 20-fold lower than in the Murchison CM2 carbonaceous chondrite. This may be due to thermal metamorphism in the Sutter's Mill parent body at temperatures greater than observed for other aqueously altered CM2 meteorites.

Infrared imaging spectroscopy with micron resolution of Sutter's Mill meteorite grains

“…Also, the amino acid analysis (Burton et al. ) suggests a higher contamination for SM12 than for SM2.…”

“…Studies of amino acids (Burton et al. ), which are present in the meteorite at only very low level, showed that SM2 and SM12 may contain amino acids of terrestrial origin, but the extent of the contamination is ambiguous.…”

The CM carbonaceous chondrite regolith Diepenveen

“…The β‐alanine to glycine ratio of Diepenveen at 1.95 is closer to that typical of CI chondrites (~2–3) than to CM chondrites (~0.5) (Burton et al. ) and indicates that the fragment analyzed experienced significant parent body alteration under mildly warmer temperatures than typical for CM chondrites. In comparison, the least known aqueously altered, and only weakly affected by thermal metamorphism CM chondrite Paris, had a ratio of 0.15 (Martins et al.…”

“…For comparison, in a terrestrial soil sample the ratio of glycine: β‐alanine: γ‐amino‐ n ‐butyric acid were measured to be 1:0.2:0.1, whereas in Diepenveen the ratio of these amino acids is 1:1.3:2.2 (Burton et al. ). The significantly higher relative abundances of β‐alanine and γ‐amino‐ n ‐butyric acid over glycine (even assuming all of the glycine is indigenous), suggest that the β‐alanine and γ‐amino‐ n ‐butyric acid in this meteorite are predominantly indigenous.…”

“…The propensity for n ‐ω amino acids has been observed in thermally altered meteorites, including CO, CV, CK, the CM Sutter's Mill, and in thermally altered CIs (Burton et al. , , , ), though in those cases the n ‐ω amino acids were primarily in the “free” form. The ratio of five‐carbon amino acids based on amine position (α‐, β‐, γ‐, and δ‐) has been shown to correlate with mineralogy and parent body alteration (e.g., Elsila et al.…”