11:30 〜 11:45
[PPS03-09] Ryugu asteroidal processes constrained by organic matter-mineral relationships: implications for the origin of life.
キーワード：Ryugu, Amino acids, Organic matter-mineral relationships, Building blocks of life, Asteroids, Aqueous alteration
Asteroids and comets represent the material that was left over after the formation of the planets. Such bodies would have initially formed from material within the protosolar nebular around the protosun and thus can preserve clues about the processes that operated during this period of the Solar System. While meteorites have revealed much about the early solar system, for organic geochemistry in particular, interpretations concerning the organic inventories of early solar system bodies have been limited by the influence of terrestrial contamination. The recent Hayabusa2 mission to the asteroid Ryugu represents an exceptional opportunity to study an almost pristine (in terms of terrestrial contamination) primitive asteroid. The results of a comprehensive geochemical analysis of 16 Ryugu samples were published by the Hayabusa2 Phase 2 curation team at the Pheasant Memorial Laboratory as an entire issue within the Proceedings of the Japan Academy, Series B, entitled “On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective” [1].
The comprehensive analysis of the Ryugu particles enabled an investigation of both mineral and organic phases. Further analysis of amino acids from the particles included in the initial comprehensive analysis, yielded quantitative amino acid abundance data [2]. In conjunction with the mineralogical information, a picture relating to the formation and evolution of soluble organic matter on the progenitor planetesimal of Ryugu was conceived. Ryugu particle A0022 was found to contain higher levels of carbonate, magnetite and Fe-sulfides, as well as evidence of mm-scale mobilization of its trace elements, compared to Ryugu particle C0008, which like the other touch down site 2 particles showed no evidence of trace element mobilization. The higher abundance of carbonate and other minerals arising from aqueous alteration for A0022, suggested that this particle had accreted more CO2-rich water ice than C0008.
Interestingly, A0022 contained lower abundances of glycine and a much higher abundance of dimethylglycine, when compared to C0008. A0022 also recorded a higher β-alanine/glycine ratio than C0008, indicating this particle had experienced higher levels of aqueous alteration, in line with the mineralogical and geochemical evidence. Dimethylglycine forms through the Eschweiler–Clarke reaction, which involves the reaction of glycine with formaldehyde and formic acid in an aqueous medium [3]. As both formaldehyde and formic acid were observed in the comet 67P/Churyumov–Gerasimenko [4], all the ingredients and conditions required for the formation of dimethylglycine during aqueous alteration on the progenitor planetesimal of Ryugu were likely present. The findings indicate that aqueous alteration did not proceed uniformly on the progenitor planetesimal of Ryugu and that aqueous alteration is important for defining the final soluble organic matter inventory of such extraterrestrial materials. As such, aqueous alteration is likely an incredibly important process for determining what building blocks of life are formed or survive to be deposited on planetary surfaces, and may thus be an essential process for determining the habitability of a given solar system.
[1] E. NAKAMURA et al., Proceedings of the Japan Academy, Series B. 98, 6, 227–282 (2022).
[2] C. Potiszil et al., Nature Communications, In Review.
[3] H. T. Clarke et al., J Am Chem Soc 55, 4571–4587 (1933).
[4] K. Altwegg et al., Monthly Notices of the Royal Astronomical Society 469, S130–S141 (2017).
The comprehensive analysis of the Ryugu particles enabled an investigation of both mineral and organic phases. Further analysis of amino acids from the particles included in the initial comprehensive analysis, yielded quantitative amino acid abundance data [2]. In conjunction with the mineralogical information, a picture relating to the formation and evolution of soluble organic matter on the progenitor planetesimal of Ryugu was conceived. Ryugu particle A0022 was found to contain higher levels of carbonate, magnetite and Fe-sulfides, as well as evidence of mm-scale mobilization of its trace elements, compared to Ryugu particle C0008, which like the other touch down site 2 particles showed no evidence of trace element mobilization. The higher abundance of carbonate and other minerals arising from aqueous alteration for A0022, suggested that this particle had accreted more CO2-rich water ice than C0008.
Interestingly, A0022 contained lower abundances of glycine and a much higher abundance of dimethylglycine, when compared to C0008. A0022 also recorded a higher β-alanine/glycine ratio than C0008, indicating this particle had experienced higher levels of aqueous alteration, in line with the mineralogical and geochemical evidence. Dimethylglycine forms through the Eschweiler–Clarke reaction, which involves the reaction of glycine with formaldehyde and formic acid in an aqueous medium [3]. As both formaldehyde and formic acid were observed in the comet 67P/Churyumov–Gerasimenko [4], all the ingredients and conditions required for the formation of dimethylglycine during aqueous alteration on the progenitor planetesimal of Ryugu were likely present. The findings indicate that aqueous alteration did not proceed uniformly on the progenitor planetesimal of Ryugu and that aqueous alteration is important for defining the final soluble organic matter inventory of such extraterrestrial materials. As such, aqueous alteration is likely an incredibly important process for determining what building blocks of life are formed or survive to be deposited on planetary surfaces, and may thus be an essential process for determining the habitability of a given solar system.
[1] E. NAKAMURA et al., Proceedings of the Japan Academy, Series B. 98, 6, 227–282 (2022).
[2] C. Potiszil et al., Nature Communications, In Review.
[3] H. T. Clarke et al., J Am Chem Soc 55, 4571–4587 (1933).
[4] K. Altwegg et al., Monthly Notices of the Royal Astronomical Society 469, S130–S141 (2017).