HomeKey points of this research results
- The chemical, isotopic and morphological compositions of macromolecular organic matter in the asteroid Ryugu samples were similar to those in primitive carbonaceous chondritic meteorites.
- The presence of macromolecular organic matter associated with phyllosilicates and carbonates in the Ryugu sample implies that much of the organic matter was modified by reaction with water on Ryugu’s parent body.
- The local enrichments of deuterium and/or nitrogen-15 indicate that some of the organic matter in Ryugu samples were formed in extreme cold environments below -200℃.
Outline
Hayabusa 2 is JAXA’s asteroid sample return mission which collected the surface samples from the carbonaceous asteroid Ryugu and returned them to the Earth for unveiling how life’s building blocks (organic molecules and water) were prebiotically formed in the early Solar System about 4.6 billion years ago.
After the return of the Ryugu samples in December 2020, the initial sample analysis has been conducted for one year. Organic macromolecule team, one of the six sub-teams in the Hayabusa 2 initial analysis team, has been led by Prof. Hikaru Yabuta, Hiroshima University. This team analyzed the elemental, isotopic, functional group compositions, structures and morphologies of macromolecular organic matter in the Ryugu samples by combining a variety of microscopic analytical techniques. The chemical and isotopic compositions of macromolecular organic matter in the Ryugu samples are similar to those in primitive carbonaceous chondritic meteorites.
This result has first proved the direct link between organic matter in the asteroid and that in meteorites. Nanometer-scale observations revealed that organic nanoglobules and diffuse organic matter were associated with phyllosilicates and carbonates in the Ryugu samples, indicating that much of the organic matter was resulted from aqueous alteration of their precursors on the Ryugu asteroidal parent body. Extreme deuterium and/or nitrogen-15 enrichments were detected from carbon-rich regions of the Ryugu samples. The isotopic features indicate that Ryugu’s organic precursors are derived from the interstellar medium or presolar nebula.
(A) Left：AFM-IR map of the Ryugu grains. Organic matter in the Ryugu grain appears as red-purple inclusions standing out from the dominant phyllosilicate signal. Colors indicate the C=O (1720 cm-1, red), C=C (1600 cm-1, blue) and Si-O (1020 cm-1, green) peaks. Upper right：AFM-IR spectrum (red) of the globule indicated in the AFM-IR map and the spectrum (green) taken in a phyllosilicate region. Lower right：Visible light image showing the location of the AFM-IR map.（Yabuta et al. 2023）
(B) Formation and evolution of macromolecular organic matter during the evolution of asteroid Ryugu（Yabuta et al. 2023）
Paper Info
Yabuta et al. (2023) Macromolecular organic matter in samples of the asteroid (162173) Ryugu, Science 379, DOI: 10.1126/science.abn9057
