[M-IS08] アストロバイオロジー

[MIS08-P08] Amino Acid Synthesis during Aqueous Alteration in Small Bodies :
A Comparison of Hexamethylenetetramine and Formaldehyde-Ammonia as Starting Materials

*方明 俊¹、藏 暁鳳¹、西内 久美子¹、上野 雄一郎¹、小林 憲正^1,2、癸生川 陽子¹ (1.東京科学大学、2.横浜国立大学)

The origin of organic compounds on Earth is a key to understand the origin of life. One prominent hypothesis proposes that organic compounds, formed in the parent bodies of meteorites, were delivered to Earth via meteorites and interplanetary dust particles. In this study, we conducted heating experiments simulating aqueous alteration in small bodies to evaluate how different starting materials and heating durations affect amino acid production. The starting materials used were formaldehyde and ammonia, both of which are abundant in comets and therefore expected to have been present in parent bodies prior to alteration (Kebukawa et al., 2017). Hexamethylenetetramine, which has been observed to form in experiments simulating interstellar ice (Bernstein et al., 2002), was also used for comparison. The results of our study revealed that formaldehyde and ammonia react immediately upon mixing to form hexamethylenetetramine, and that hexamethylenetetramine is almost completely consumed after being heated at 150°C for 72 hours. Moreover, a strong negative correlation was found between the concentration of amino acids and that of hexamethylenetetramine during the 72-hour heating period. This suggests that hexamethylenetetramine undergoes hydrolysis, breaking down into formaldehyde and ammonia, which then serve as precursors for amino acid synthesis. Given that hexamethylenetetramine is less volatile than formaldehyde and ammonia, it is plausible that it could have acted as a precursor for organic compound synthesis even within the inner regions of the ammonia snow line. Furthermore, although amino acid production initially increased with heating time, it began to decrease after a certain point, indicating that more complex organic compounds were likely synthesized through glycine as an intermediate.

References:
Bernstein, M. P. et al., Nature, 416(6881), 401-404 (2002)
Kebukawa, Y. et al., Sci. Adv. 3, e1602093 (2017)