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Comets and asteroids are among the most pristine objects in the Solar System, being formed out of the materials available in the proto-Solar Nebula 1. Especially interesting are the complex organic molecules in these bodies, as they likely contribute towards the elemental composition of forming planets, as well as potentially being delivered after accretion of planetary bodies via impacts and thus contribute to their molecular inventory 2, 3.Many primitive solar system objects, such as carbonaceous chondrites or interplanetary dust particles (IDPs), contain organic matter, which itself can be divided into a solvent-soluble (soluble organic matter, SOM) and insoluble fraction (Insoluble Organic Matter, IOM) 4, 5. The soluble fraction can contain PAHs, sugars, nucleobases, and amino acids 6, 7, 8, 9. The insoluble fraction is a mix of large macromolecules with numerous molecular links and functional groups 3, 14. The formation environment of the IOM is an area of ongoing research and IOM could have formed either in the interstellar medium or in the proto-Solar Nebula 3.In the proto-Solar Nebula, interstellar space, and protoplanetary disks, microscopic ice-coated dust grains are readily available. Laboratory experiments on the energetic processing of extraterrestrial and interstellar ice analogues show that a number of complex molecules form, including prebiotic molecules e.g., 10, 11, 12, 13, 14, therefore focussing on recreating the chemical inventory observed in SOM. Even though it makes up the majority of the organic carbon in solar system objects, IOM has not been extensively studied in the laboratory. However, the formation pathways of IOM are crucial to understand the complex insoluble organic molecules available for the formation of planetary bodies.MethodsIn this study, irradiation experiments on ice are performed with the ICEBEAR setup 15. The setup consists of a stainless-steel vacuum chamber with base pressures of
Kipfer et al. (Wed,) studied this question.