Abstract
Ice mantles of interstellar dust particles in molecular clouds are one of the most suitable sites for prebiotic molecular formation. Organic compounds including amino acid precursors are thought to have been produced by galactic cosmic ray irradiation in the ice mantle of interstellar dust particles in molecular clouds. Previous studies have shown that macromolecular amino acid precursors (CAW) are produced from carbon monoxide, ammonia, and water abiotically in experiments simulating molecular cloud environments. 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 the interior of small bodies. Amino acids (glycine, alanine, valine, Isovaline, alpha-aminobutyric acid, alpha-aminoisobutyric acid) or CAW was dissolved in ammonia aqueous solution or in an aqueous solution of formaldehyde and ammonia. These solutions were irradiated with gamma-rays from 60Co source. The results showed that the macromolecular amino acid precursors (CAW) were more stable than free amino acids against gamma-ray irradiations. Moreover, we confirmed that amino acid precursors could be newly synthesized by gamma-ray irradiation.
