Stability of Amino Acids and Their Precursors of Interstellar Origin in the Interior of Small Bodies

Abstract

In the interstellar environment, icy dust particles in molecular clouds are one of the most suitable sites for prebiotic molecular formation. Organic compounds including amino acids are thought to have been produced by galactic cosmic ray irradiation in the ice mantle around the nucleus of dust particles in molecular clouds. Previous studies have shown that macromolecular amino acid precursors (CAW) are produced abiotically in experiments simulating molecular clouds. It was possible that the amino acid precursors produced in interstellar molecular clouds were incorporated into the primitive small bodies during the solar system formation and were affected by gamma-rays and heat from the radioactive decay of ²⁶Al. Considering these factors, experiments were conducted to investigate the stability of amino acids and macromolecular amino acid precursors against gamma-rays in simulated interiors of small bodies. Glycine or CAW was dissolved in ammonia water or in a mixture of formaldehyde, ammonia, and water, and was irradiated by gamma-rays from ⁶⁰Co source. The results showed that macromolecular amino acid precursors from molecular clouds were more stable than free amino acids against gamma-ray irradiations, in an environment that simulates the interior of small bodies.