Abstract EANA2025-38

Carbon-rich matter is found in a variety of Solar System objects. Primitive small bodies such as asteroids and comets show a rich chemical inventory of organic molecules [1, 2]. Organics are also revealed on the surface of trans-Neptunian objects (TNOs) [3]. A relevant fraction of these materials is expected to have originated at the dawn of the Solar System or even earlier, in the interstellar medium, where species of astrobiological relevance are expected to form [4].
The harsh conditions of the Solar System formation would challenge the survival of organic matter. Energetic radiation and thermal processing in the protosolar envelope and in the disk could severely alter carbon-rich materials up to their destruction. It is thus necessary to shed light on the alteration of pristine organics to understand if they can survive enough to be incorporated by small bodies.
We thus produce laboratory simulants of the macromolecular organic matter formed by chemical processes involving energetic radiation in the ISM and during the formation of the Solar System, namely organic refractory residues (ORRs) and we thermally-process them up to 973 K. Experiments are performed at the Laboratory for Experimental Astrophysics (LASp) at INAF-Astrophysical Observatory of Catania (Italy) and at the Institute of Space Research, DLR, Berlin (Germany). Samples are produced in ultra-high vacuum and on inert substrates at 18 K by exposing H-, C-, N-, O-bearing frozen compounds to a 200 keV ion beam. The process is meant to simulate the bombardment of ices ubiquitous in star-forming regions by low-energy galactic cosmic rays (GCR) []. The warm-up of processed ices to 300 K, simulating the heating taking place during the formation of the Sun, determines the formation of ORRs. These samples are then annealed to shed light on their decay with increasing temperature.
We use mid-infrared spectroscopy to follow the decay of the main absorption features of organic matter during heating, and we inform on the chemical changes in annealed samples. Samples produced with varying ice mixtures and irradiation doses show diverse resistance to annealing. At the highest temperature we investigate, no infrared features can be detected although Raman spectroscopy performed at the Max Plank Institute for Extraterrestrial Physics, Garching (Germany), and at LASp allows us to detect the formation of amorphous carbon. Some of the properties of amorphous carbon can also be related to the initial ice mixture and irradiation dose.
Our study provides constraints on the temperatures that determine the change of spectral features of organic matter, up to its destruction. We provide implications for the origin and presence of organic matter in primitive bodies and on the alteration expected on the astrobiological relevance of these altered materials.

References
[1] Altwegg, K., et al. 2017, MNRAS, 469, S130
[2] Nakamura, T., et al. 2023, Science, 379, abn8671
[3] Pinilla-Alonso, N., et al. 2025, Nature Astronomy, 9, 230
[4] Urso, R. G., et al. 2020, A&A, 644, A115
[5] Rothard, H., et al. 2017, J. Phys. B, 50, 062011