Unveiling the Chemical Origins of the Solar System through Ground-Based Infrared Spectroscopy of Comets

The composition of comets provides key insights into the physical, chemical, and evolutionary processes that shaped our and other planetary systems [1]. Furthermore, it can reveal whether the material in our Solar System was primarily inherited from the proto-solar nebula or reprocessed during its formation [2,3].

Ground-based high-resolution infrared spectroscopy (∼2 to 5 μm) reveals a complex chemical heterogeneity in comets [4,5], which may be consistent with the numerous processes that may have occurred in our protoplanetary disc during their formation [2,3,6], as well as the dynamical models that predict their dispersion into current reservoirs after formation [7]. This makes it difficult to chemically categorize comets and link the observed differences to their specific formation site. Nevertheless, with improved global observing facilities and instrumentation, the amount of available data has increased, allowing for a more accurate statistical approach.

Here, we present the statistical analysis of molecular abundances of a few species in 35 comets as measured by infrared high-resolution spectroscopy [8]. Our research aims to: (i) explore for significant differences across dynamical families (e.g., Jupiter-family/short-period vs. Oort-Cloud/long-period comets) that could be linked to disk processes and/or comet material evolution after storage; (ii) search and possibly compensate for observational biases in the data; (iii) find potential taxonomical classes for comets, and (iv) compare  the molecular abundance ratios measured in comets with those retrieved in planet-forming systems. Our database also includes recent results relative to comets observed with CRIRES⁺ at VLT/ESO (among them C/2023 A1 (Leonard) [9] and C/2023 H2 (Lemmon) [10]), which will be displayed individually to demonstrate this instrument capabilities.

Among other findings, we will show the existence of significant biases correlated to the observing conditions for specific molecular species (e.g., the excess of H₂CO in comets observed within 1 au from the Sun), and how these biases may influence our understanding of the comet chemistry in the context of planet formation. We will compare the database’s averaged molecular abundances to those obtained by the ESA-Rosetta mission [11], revealing significant differences between 67P/Churyumov-Gerasimenko and other comets. Finally, we will illustrate how the overall results can be generalized to planet formation by comparing molecular abundance ratios (such as [CH₃OH]/[H₂CO]) in comets and planet-forming systems.

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