Impact of environmental conditions on organic matter in astrophysical ice analogues

The existence of organic matter presenting a high molecular diversity in extraterrestrial environments is well documented. To understand the origin of this organic diversity, laboratory experiments were developed and showed that irradiation and thermal alteration of simple molecules such as methanol, water, and ammonia in conditions mimicking astrophysical ice environments. Ices containing water, methanol, and ammonia (H₂O: MeOH: NH₃) photolyzed and monitored by infrared spectroscopy, while the organic matter formed at room temperature was analyzed in situ with infrared spectroscopy and ex situ with high-resolution mass spectrometry. Those ices irradiated at 77 K and 10^-8 mbar shows a significant organic molecular diversity: residual organic compounds contain up to 78 C, 188 H, 123 N, and 37 O. Most of them contains all four CHNO atoms (76-86 per cent), followed by CHO (11-17 per cent), and CHN compounds (5-6 per cent). CHNO and CHO compounds are more aliphatic (34-53 per cent), while CHN compounds are mostly condensed aromatics (83-90 per cent). In this work, our objective is to investigate impacts of environment on this organic molecular diversity by focusing on three parameters: photon dose, pressure, and heating rate during the warming process. Analyses of the residue formed showed that the heating rate and pressure weakly alter the abundance of the final organic material, while the irradiation rate reduced its abundance at high photon doses by a factor of 8. These results give insights on the impact of icy environment conditions in the evolution of astrophysical organic matter.