Spontaneous Generation of Amino Acid Structures in the Interstellar Medium

Abstract

In dense interstellar clouds dust particles accrete ice mantles. As seen in infrared (IR) observations, this ice layer consists mainly of water ice, but also of carbon and nitrogen containing molecules. We deposited a gas mixture consisting of H₂O, CO₂, CO, CH₃OH, and NH₃ onto an aluminium surface at 12 K under high vacuum, 10^-7 mbar. During deposition the molecules were subjected to ultraviolet radiation with main intensity at Lyman-α. After warm-up, the refractory material was extracted from the aluminium block, hydrolysed for 24 h at 110 °C with 6 M HCl, derivatized and finally analysed by enantioselective gas chromatography coupled to a mass spectrometer. We were able to identify 16 amino acids in the room temperature products of irradiation. The results were confirmed by parallel experiments using ¹³C-labelled ices in order to exclude contamination. A first ‘group’ of the identified amino acids was suggested to serve as the precursors of peptides and proteins. A second ‘group’ namely the diamino carboxylic acids is assumed to contribute to the development of the first genetic material, the peptide nucleic acid PNA. Beside the two groups of amino acids, N-heterocyclic organic molecules were identified that resemble the molecular building block of biological cofactors. The obtained results support the assumption that the photochemical products could be preserved in interstellar objects, and in term be delivered to the Earth during the heavy bombardment which ended about 3.8 Gyr ago, where they triggered the appearance of live.