Formation of amino acid precursors in early aqueous alteration in small bodies: Synergetic effects of gamma rays and hydrothermal processing

Abstract

Organic compounds such as amino acids may have been delivered to the early Earth via carbonaceous chondrites and interplanetary dust particles. Mineralogical and petrological evidence has shown that liquid water was formed from water ice in the early stages of the formation of the parent bodies of carbonaceous chondrites, due to the heat from the radioactive decay of short-lived radionuclides such as ²⁶Al. In previous research, amino acid precursors were produced from aqueous solutions containing formaldehyde and ammonia by hydrothermal experiments and gamma-ray irradiation experiments to evaluate organic formation during aqueous alteration processes in meteorite parent bodies. However, the differences in the effects and reactions of gamma rays and heating, as well as the synergetic effects, are not well understood. In this study, both heating and gamma irradiation were applied to aqueous solutions containing formaldehyde, methanol, and ammonia to investigate the synergistic effects of heating and gamma rays on amino acid formation. The results showed that gamma irradiation followed by heating was more efficient in producing amino acid precursors compared to heating followed by gamma irradiation. The characteristic features of UV-visible and fluorescence spectra of the experimental products were consistent with Maillard-type reactions, suggesting that Maillard-type reactions led to the formation of amino acid precursors.