Tokyo Institute of Technology

Hokkaido University

Graduate School of Science, The University of Tokyo

Summary of Presentations

A research group led by Professor Tetsuya Yokoyama of the Department of Earth and Planetary Science, Graduate School of Science, Tokyo Institute of Technology, Professor Naoyoshi Yurimoto of the Graduate School of Science, Hokkaido University, and Professor Shogo Tachibana of The University of Tokyo has measured the isotopic composition of copper and zinc in the Cb-type asteroid "Ryugu" and found that Ryugu-like material originating from the outer solar system also exists on Earth. They found that Ryuguu-like material originating from the outer solar system also exists on Earth, amounting to about 5% of the Earth's mass.

Initial analysis of the Ryuguu samples revealed that the Cb-type asteroid Ryuguu has a chemical and isotopic composition similar to that of Ivena-type carbonaceous meteorites. However, the isotopic compositions measured so far are for difficult-to-volatile elements ( titanium, chromium, and iron) and highly volatile elements (oxygen, etc.), and there was no information on isotopic compositions for moderately volatile elements, which are important in discussing the formation process of the Earth.

The research group measured the isotopic compositions of copper and zinc, which are moderately volatile elements, and found that the analyzed values of Ryuguu and Ivna-type carbonaceous meteorites are consistent. The isotopic compositions of copper and zinc in Ryuguu and Ivna-type carbonaceous meteorites are clearly different from those of other carbonaceous meteorites. This is consistent with the conclusion drawn from the isotopic analysis of Liugu's titanium, iron, and chromium, namely, that Liugu and the Ivna-type carbonaceous meteorites originated in completely different places from other meteorites. Furthermore, a comparison of the zinc isotopic compositions of Ryuguu and the Earth inferred that about 30% of the zinc present on Earth is derived from Ryuguu-like material. This suggests that the material that existed in the outer solar system where Ryuguu was born also contributed to the formation of the Earth, and the amount is expected to be about 5% of the Earth's mass.

The research results will be published online in Nature Astronomy on December13, 2022 (Japan Standard Time).

Figure: Cu and Zn isotopic compositions of Ryugu sample ( Ryugu), Ivna-type carbonaceous meteorites ( CI, in purple range), and other carbonaceous meteorites ( C-ung, CM, CV, CO ). Alais,Orgueil,Tarda,Murchison, andAllende are the names of the meteorites. (© Paquet et al., 2022 with some modifications).

For more information, please visit the Tokyo Institute of Technology website.