Abstract DGP2026-79

A variety of primitive bodies in the Solar System exhibit the presence of carbon-rich matter. Observations of asteroids, comets, and trans-Neptunian objects (TNOs) and the analysis of meteorites, interplanetary dust particles (IDPs), and samples returned by space missions provide information on the rich and diverse chemical inventory of extraterrestrial organics [1, 2, 3, 4]. A significant fraction of these materials is expected to be pristine, preserving a record of the chemistry at work at the dawn of the Solar System or even earlier, in the interstellar medium [5]. However, the harsh conditions during the Solar System formation, including ionizing radiation and thermal processing in the protosolar envelope and in the disk, would challenge the survival of organic matter, leading to its alteration or destruction [6]. Understanding the changes induced in organic compounds by processing prior to their incorporation into small bodies would therefore shed light on the conditions during the bodies formation.

We performed experiments to shed light on the role of thermal processing on complex organic materials. We produced laboratory simulants of the macromolecular organic matter possibly present during the formation of the Solar System, namely organic refractory residues (ORRs) and followed their evolution with increasing the temperature. ORRs were produced at the Laboratory for Experimental Astrophysics (LASp) at INAF-Astrophysical Observatory of Catania (Italy) and further processed at the Institute of Space Research, DLR, Berlin (Germany). ORRs were 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 in the presolar cloud by low-energy galactic cosmic rays (GCR) [8]. 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 [8, 9]. ORRs were then annealed to about 1000 K to shed light on the alteration induced by the increasing temperature, simulating the thermal processing in the protoplanetary disk.
During each experimental step, we analyze samples by means of mid-infrared spectroscopy and we identify absorption features that inform on the chemical changes during the processing. 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, but 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.

We provide constraints on the temperatures that drive changes in the spectral features of organic matter, up to its destruction. We also discuss possible evidence of thermally-processed organics in outer Solar System bodies.

References

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