High molecular diversity of extraterrestrial organic matter in Murchison meteorite revealed 40 years after its fall

Abstract

Numerous descriptions of organic molecules present in the Murchison meteorite have improved our understanding of the early interstellar chemistry that operated at or just before the birth of our solar system. However, all molecular analyses were so far targeted toward selected classes of compounds with a particular emphasis on biologically active components in the context of prebiotic chemistry. Here we demonstrate that a nontargeted ultrahigh-resolution molecular analysis of the solvent-accessible organic fraction of Murchison extracted under mild conditions allows one to extend its indigenous chemical diversity to tens of thousands of different molecular compositions and likely millions of diverse structures. This molecular complexity, which provides hints on heteroatoms chronological assembly, suggests that the extraterrestrial chemodiversity is high compared to terrestrial relevant biological- and biogeochemical-driven chemical space.

Fig. 1.

Progressive detailed visualization of the methanolic Murchison extract in the ESI(−) FTICR/MS spectra in the mass ranges (A) 150–1,000 Da, (B) 315–324 Da, (C) 318.9–319.4 Da, and (D) 319.130–319.142 Da with credible elemental formula assignments; (E) the bars (red/green) correspond to all 14 possible CHNOS compounds (N, S ≤ 4) in this mass range, which more than half (8 out of 14) were found in the experimental data (green). (F) Frequency of assigned elemental formulas as a function of the allowed error windows. (G) Distribution of the number of signals per nominal mass [for ESI(+) mode see Fig. S1].

Fig. 2.

Extraction efficiency of the solvents. (A) Number of total elemental compositions found in ESI(−) mode for the various extraction solvents classified into CHO, CHOS, CHNO, CHNOS molecular series with (B) relative distributions of the 14,197 unique compositions attributed to molecular formulas (Table 1). (C) Analogous counts and distributions for the ESI(+) mode. (D) Section of ESI(−) FTICR/MS spectra between m/z 318.95 and 319.40 Da (nominal mass of neutrals 320 Da) for all solvents, demonstrating the huge chemical diversity of selective extracts.

Fig. 3.

Integrated representations of the molecular diversity in the methanol extracted fraction, derived from ESI(−) FTICR/MS spectra in the (A) 150–700 m/z range. (B–D) Relationships between m/z, H/C, and O/C elemental ratios corresponding to the mass spectra shown in A.

Fig. 4.

Distribution of mass peaks within the CHO, CHOS, CHNO, and CHNOS series for molecules with 19 carbon atoms. CHO and CHOS series exhibit increasing intensities of mass peaks for aliphatic (hydrogen-rich) compounds, whereas CHNO and CHNOS series exhibit a slightly skewed near Gaussian distribution of mass peaks with large occurrences of mass peaks at average H/C ratio. The apparent odd/even pattern in the CHNO and CHNOS series denotes occurrence of even (N₂) and odd (N_1,3) counts of nitrogen atoms in CHNO(S) molecules in accordance with the nitrogen rule (Fig. S8E).