Gamma-Ray-Induced Synthesis of Sugars in Meteorite Parent Bodies

Sugars play an indispensable role for all living organisms. Given that certain sugars have been identified in carbonaceous chondrites, these compounds might have been delivered to the early Earth via meteorites. The genesis of these sugars, however, has been a subject of debate; they are considered to have either originated from UV irradiation of interstellar ice or from hydrothermal reactions within the environments of meteorite parent bodies. The parent bodies of carbonaceous chondrites contained water ice which underwent hydrothermal alteration as a result of the internal warming of these bodies. The most likely source of this heat is believed to be the decay of radioactive nuclides, such as Al-26. In our previous research, we demonstrated that gamma-ray exposure significantly enhances the synthesis of amino acids from aqueous solutions of formaldehyde, ammonia, and methanol. Nonetheless, the impact of radiation on sugar formation has not been investigated. Hence, the current study is conducted with a focus on the formation of aldose sugars through gamma-ray irradiation to such solution mixtures. Our results reveal that gamma-rays indeed promote the formation of sugars, including ribose, without the presence of a catalyst such as glycolaldehyde. Furthermore, we demonstrated that the presence of ammonia enhanced the yield of aldose sugars, although higher concentration of ammonia inhibited sugar production. Our findings suggest that gamma-rays from the decay of Al-26 played a significant role in the formation of sugars during low-temperature aqueous alteration inside meteorite parent bodies.