Re-characterization of complex organic molecules and their fragments in comet 67P

Nitrogen, oxygen, phosphorus, and sulfur are key elements in carbon-based biochemistry, and in-situ comet missions are a unique opportunity to study these elements' prevalence in pristine organics.  A milestone was ESA's Rosetta mission, which investigated comet 67P/Churyumov-Gerasimenko (hereafter 67P). The on-board high-resolution Double Focusing Mass Spectrometer (DFMS), part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA; Balsiger et al. 2007) analyzed the chemical composition of 67P in great detail (Altwegg et al. 2019). Subsequent studies revealed a plethora of complex organic molecules reaching from pure hydrocarbons (Hänni et al. 2022), O-bearing molecules (Hänni et al. 2023), N-bearing compounds (Hänni et al. 2025) as well as dimethyl sulfide (Hänni et al. 2024). In these previous studies, the chemical species formed during the experiments were primarily identified based on signals corresponding to their molecular masses and (major) fragments produced by electron-impact in the mass spectra. However, such an approach can lead to ambiguities, as best-fitting molecules are hand-picked, introducing human bias and error propagation. In addition, isomers with similar fragmentation patterns further increase such degeneracies.

In this work, the previously acquired mass spectra will therefore be reanalyzed using a Monte Carlo-based deconvolution approach (Gautier et al. 2020) to obtain a more standardized, reproducible, and intercomparable interpretation of the chemical composition. By statistically exploring large numbers of possible combinations of candidate molecules and their associated fragmentation patterns, this method aims to disentangle overlapping contributions in the spectra and improve the identification of true molecular compounds while minimizing misassignments caused by fragmentation artifacts.

Introducing this statistical approach standardizes the analysis procedure and reduces the influence of human bias on the spectral interpretation, while also testing whether the results align with previous studies. Furthermore, the results will be compared to those reported by the Cometary Sampling and Composition Experiment (COSAC; Goesmann et al. 2007) aboard the Philae lander, where the same software was used for the deconvolution of the mass spectra (Leseigneur et al. 2022).

 

References:

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Gautier, T., Serigano, J., Bourgalais, J., Hörst, S. M., & Trainer, M. G. (2020). Decomposition of electron ionization mass spectra for space application using a Monte‐Carlo approach. Rapid Communications in Mass Spectrometry, 34(8), e8684.

Goesmann, F., Rosenbauer, H., Roll, R., Szopa, C., Raulin, F., Sternberg, R., ... & Munoz-Caro, G. (2007). COSAC, the cometary sampling and composition experiment on Philae. Space Science Reviews, 128(1), 257-280.

Hänni, N., Altwegg, K., Combi, M., Fuselier, S. A., De Keyser, J., Rubin, M., & Wampfler, S. F. (2022). Identification and characterization of a new ensemble of cometary organic molecules. Nature Communications, 13(1), 3639.

Hänni, N., Altwegg, K., Baklouti, D., Combi, M., Fuselier, S. A., De Keyser, J., ... & Wampfler, S. F. (2023). Oxygen-bearing organic molecules in comet 67P’s dusty coma: First evidence for abundant heterocycles. Astronomy & Astrophysics, 678, A22.

Hänni, N., Altwegg, K., Combi, M., Fuselier, S. A., De Keyser, J., Ligterink, N. F., ... & Wampfler, S. F. (2024). Evidence for abiotic dimethyl sulfide in cometary matter. The Astrophysical Journal, 976(1), 74.

Hänni, N., Altwegg, K., Baklouti, D., Combi, M., Fuselier, S. A., De Keyser, J., ... & Wampfler, S. F. (2025). Nitrogen-and nitrogen-oxygen-bearing organic molecules in comet 67P/Churyumov-Gerasimenko: An untargeted investigation. Astronomy & Astrophysics, 699, A135.

Leseigneur, G., Bredehöft, J. H., Gautier, T., Giri, C., Krüger, H., MacDermott, A. J., ... & Goesmann, F. (2022). ESA's Cometary Mission Rosetta—Re‐Characterization of the COSAC Mass Spectrometry Results. Angewandte Chemie International Edition, 61(29), e202201925.