O-bearing molecules in comet 67P revisited: evidence for abundant heterocycles

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Alongside meteorites, impacting comets are considered a major source of pristine organic matter delivered to the early Earth, see, e.g., Rubin et al. (2019). Their chemical inventory, hence, is a key towards understanding prebiotic chemistry and the processes that led to the evolution of carbon-based life on Earth. For comet 67P/Churyumov-Gerasimenko (hereafter 67P), especially the high-resolution Double Focusing Mass Spectrometer (DFMS) – part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA; Balsiger et al. 2007) onboard the European Space Agency’s Rosetta spacecraft – obtained data that allows the study of this comet’s chemical composition in unprecedented detail (LeRoy et al. 2015, Schuhmann et al. 2019). For the time period around its perihelion in early August 2015, the comet was very active and extensive dust ejection was observed (Vincent et al. 2016). Decoupled from the cometary surface, the dust particles heat up and sublimation of also larger molecules is enhanced. Relying on reference spectra – either calibrated or from the database of the National Institute of Standards and Technology –, Hänni et al. (2022) showed how the mass spectrum of pure hydrocarbon species could be fully deconvolved, which led to the identification of new cometary organic species. Following the same approach, also heteroatom-bearing species can be investigated. After the pure hydrocarbon species, O-bearing organic molecules of the general formula CnHmOx (where n = 1-8, m = 0-14, and x = 1-2) depict the second-most abundant group of cometary volatile organics. This group of species is in the focus of our ongoing work, not only for their comparably high abundance in comets but also for their prebiotic relevance. The heteroelement O is common in biomolecules such as fatty acids, amino acids, and sugars. For the first time and with great certainty, we confirm abundant heterocycles like furan and pyran (including several derivatives), which have been long sought but not yet detected in the Interstellar Medium (ISM; Barnum et al. 2022). The presence especially of furan is of great interest because of the furanose moiety in the sugar/phosphate backbone of (deoxy)ribonucleic acid. Eventually, we compare and contrast 67P’s updated and extended inventory of O-bearing organic molecules to other comets (Biver and Bockelée-Morvan 2019) and the ISM (McGuire 2022), showing that our data delivers evidence for many new species. Rubin et al. ACS Earth Space Chem. 2019, 3, 1792−1811.Balsiger et al. Space Sci. Rev. 2007, 128, 745-801.Le Roy et al. Astron. Astrophys. 2015, 583, A1.Schuhmann et al. ACS Earth Space Chem. 2019, 3, 1854–1861.Vincent et al. MNRAS 2016, 462 (Suppl_1), 184-194.Hänni et al. Nat. Commun. 2022 13:3639.Barnum et al. J. Phys. Chem. A 2022, 126, 2716−2728.Biver and Bockelée-Morvan ACS Earth Space Chem. 2019, 3, 1550−1555.McGuire The Astrophysical Journal Supplement Series 2022, 259:30, 51.