Japan Aerospace Exploration Agency

Hokkaido University

Tokyo Institute of Technology

Tohoku University

Kyoto University

Kyushu University

Hiroshima University

The University of Tokyo

Summary

The chemical and isotopic compositions of samples from the asteroid Ryuguu brought back by Hayabusa2 were measured. Ryuguu was found to be composed mainly of carbonaceous meteorites, especially Ivena-type carbonaceous meteorites called CI chondrites. Its main constituent minerals are secondary minerals precipitated from aqueous solutions in Ryuguu's parent body. The aqueous solution in the parent body altered the primary minerals originally on Ryuguu and deposited these secondary minerals about 5 million years after the birth of the solar system. The temperature at that time was about 40°C and the pressure was over 0.06 atm. Subsequently, to this day, the Ryuguu samples brought back to the site are not believed to have been heated above 100°C. Based on these results, it can be said that the Ryuguu sample has the most primitive characteristics of any natural sample available to mankind, including meteorites that have been found so far, and has not been differentiated in terms of chemical composition. In the future, the Ryuguu sample will be used internationally as a new solar system reference sample.

The results of this research have been published in Science.

Figure: Elemental abundances in the Ryuguu sample, normalized by CI chondrite analysis values; points above (below) 1.0 indicate elements contained in larger (smaller) amounts than in CI chondrites. (From ©Yokoyama et al., 2022)

Professor Shogo Tachibana of the Institute of Space and Planetary Science (ISAS) participated in the research results.

For more information, please visit the website of the Institute of Space and Astronautical Science (ISAS) of JAXA.