Raman analysis of organic refractory materials after energetic processing: Evidence for amorphous carbon on TNOs and comets

Amorphous carbon (αC) is found in various extraterrestrial particles, including those thought to originate from the outer Solar System. αC can form through two main processes involving C‐rich materials: exposure to energetic charged particles and thermal processing. Laboratory analyses can constrain the origin of αC in space, as it is not easily detectable through remote sensing. We here investigate the formation of αC on the icy surface of Trans‐neptunian objects and Oort cloud comets throughout their exposure to energetic ions. We use organic refractory residues (ORRs), which are laboratory simulants of refractory organics in space, obtained from the irradiation (200 keV ions) of various icy mixtures (N 2 , CO, CH 4 , CH 3 OH). As formed ORRs were further irradiated at room temperature (αC‐ORRs) and analyzed by Raman spectroscopy. Our as formed ORRs do not exhibit αC that is in turn detected in αC‐ORRs. The carbonaceous structure of αC‐ORRs shows high disorder and dependence on the initial icy composition. Nitrogen‐bearing αC‐ORRs exhibit structural properties similar to some extraterrestrial particles likely originating from icy outer bodies, whereas annealed αC‐ORRs mimic materials that underwent different degrees of metamorphism. Our findings highlight how Raman characterization of αC in extraterrestrial samples serves as a strong analysis tool in providing insights into the evolution of different Solar System objects.