New Analysis Unveils True Nature of Ancient Asteroid

Direct samples from near-Earth asteroid Ryugu provide scientists a glimpse into the raw materials of solid matter in the outer regions of the early solar system.

Since as far back as Ancient Greece, humans have been fascinated by the solar system. However, Japanese researchers have now collected asteroid data that provides insights into the development of the solar system that earlier scientists such as Ptolemy, Galileo, and Copernicus could only have dreamed of.

Asteroid explorer Hayabusa2, launched in 2014, set out for Ryugu, a carbon-rich C-type asteroid. In 2018, it arrived in the area of Ryugu, conducting a number of remote observations and collecting samples from two locations on the asteroid. Before the launch of Hayabusa2, a research team at Osaka University had been developing a non-destructive method of light element analysis utilizing muons to analyze Ryugu.

(Left) An example of a muonic X-ray created after a muon is captured by an irradiated material. (Right) The sample obtained from the asteroid Ryugu. Credit: (left) Muon analysis team, (right) JAXA

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Against such a backdrop, an initial analysis project involving international researchers began in 2021, conducted by Dr. Nakamura of Tohoku University, leader of the “Stone Analysis Team” from the Hayabusa2 Initial Analysis Team. The information expected to come from the Ryugu stone is diverse, and the Stone Analysis Team carried out various studies on the shape of the stone as well as its elemental distribution and mineral composition. The Osaka University research group was interested in the type and quantity of the elements that Ryugu contains, particularly the light elemental composition (C, N, O) of the material substance of life, and joined the initial analysis team.

Figure 2: Comparison between muonic X-ray spectra from the Ryugu sample and the Orgueil CI chondrite. Credit: Muon Analysis Team

One of the advantages of muon analysis is that the high penetrating power of muon characteristic X-rays makes it possible to non-destructively identify elements inside a sample.

Data obtained from the Ryugu samples (figure 2) are consistent with the classification of Ryugu as a CI chondrite, clearly suggesting that the Ryugu rocks are extremely primordial material in the solar system. A further important finding is that the asteroid contains 25% less oxygen relative to silicon than typical CI chondrite meteorites that have impacted Earth (figure 3). This suggests that CI chondrites, which were previously regarded as a benchmark for the chemical compositions of solid materials in the solar system, may in fact record some contamination from terrestrial materials.

Figure 3: Comparison of the elemental compositions of the Ryugu sample and the Orgueil CI chondrite (K. Lodders, The Astrophysical Journal, 591, 1220–1247, 2003), showing the relatively lower oxygen content in the Ryugu sample compared with CI chondrite. Credit: Muon Analysis Team

Professor Terada says “Carbon, nitrogen, and oxygen are the material substances of life. Therefore, our successful detection of these substances without destroying the Ryugu samples is a groundbreaking achievement.”

Given that analysis of the pristine samples from Ryugu provides a rare opportunity to compare material obtained directly from the asteroid with meteorites on Earth, the new data from the Ryugu samples may help to redefine the standard elemental compositions of solid materials in the solar system.

Reference: “Formation and evolution of carbonaceous asteroid Ryugu: Direct evidence from returned samples” by T. Nakamura, M. Matsumoto, K. Amano, Y. Enokido, M. E. Zolensky, T. Mikouchi, H. Genda, S. Tanaka, M. Y. Zolotov, K. Kurosawa, S. Wakita, R. Hyodo, H. Nagano, D. Nakashima, Y. Takahashi, Y. Fujioka, M. Kikuiri, E. Kagawa, M. Matsuoka, A. J. Brearley, A. Tsuchiyama, M. Uesugi, J. Matsuno, Y. Kimura, M. Sato, R. E. Milliken, E. Tatsumi, S. Sugita, T. Hiroi, K. Kitazato, D. Brownlee, D. J. Joswiak, M. Takahashi, K. Ninomiya, T. Takahashi, T. Osawa, K. Terada, F. E. Brenker, B. J. Tkalcec, L. Vincze, R. Brunetto, A. Aléon-Toppani, Q. H. S. Chan, M. Roskosz, J.-C. Viennet, P. Beck, E. E. Alp, T. Michikami, Y. Nagaashi, T. Tsuji, Y. Ino, J. Martinez, J. Han, A. Dolocan, R. J. Bodnar, M. Tanaka, H. Yoshida, K. Sugiyama, A. J. King, K. Fukushi, H. Suga, S. Yamashita, T. Kawai, K. Inoue, A. Nakato, T. Noguchi, F. Vilas, A. R. Hendrix, C. Jaramillo-Correa, D. L. Domingue, G. Dominguez, Z. Gainsforth, C. Engrand, J. Duprat, S. S. Russell, E. Bonato, C. Ma, T. Kawamoto, T. Wada, S. Watanabe, R. Endo, S. Enju, L. Riu, S. Rubino, P. Tack, S. Takeshita, Y. Takeichi, A. Takeuchi, A. Takigawa, D. Takir, T. Tanigaki, A. Taniguchi, K. Tsukamoto, T. Yagi, S. Yamada, K. Yamamoto, Y. Yamashita, M. Yasutake, K. Uesugi, I. Umegaki, I. Chiu, T. Ishizaki, S. Okumura, E. Palomba, C. Pilorget, S. M. Potin, A. Alasli, S. Anada, Y. Araki, N. Sakatani, C. Schultz, O. Sekizawa, S. D. Sitzman, K. Sugiura, M. Sun, E. Dartois, E. De Pauw, Z. Dionnet, Z. Djouadi, G. Falkenberg, R. Fujita, T. Fukuma, I. R. Gearba, K. Hagiya, M. Y. Hu, T. Kato, T. Kawamura, M. Kimura, M. K. Kubo, F. Langenhorst, C. Lantz, B. Lavina, M. Lindner, J. Zhao, B. Vekemans, D. Baklouti, B. Bazi, F. Borondics, S. Nagasawa, G. Nishiyama, K. Nitta, J. Mathurin, T. Matsumoto, I. Mitsukawa, H. Miura, A. Miyake, Y. Miyake, H. Yurimoto, R. Okazaki, H. Yabuta, H. Naraoka, K. Sakamoto, S. Tachibana, H. C. Connolly, D. S. Lauretta, M. Yoshitake, M. Yoshikawa, K. Yoshikawa, K. Yoshihara, Y. Yokota, K. Yogata, H. Yano, Y. Yamamoto, D. Yamamoto, M. Yamada, T. Yamada, T. Yada, K. Wada, T. Usui, R. Tsukizaki, F. Terui, H. Takeuchi, Y. Takei, A. Iwamae, H. Soejima, K. Shirai, Y. Shimaki, H. Senshu, H. Sawada, T. Saiki, M. Ozaki, G. Ono, T. Okada, N. Ogawa, K. Ogawa, R. Noguchi, H. Noda, M. Nishimura, N. Namiki, S. Nakazawa, T. Morota, A. Miyazaki, A. Miura, Y. Mimasu, K. Matsumoto, K. Kumagai, T. Kouyama, S. Kikuchi, K. Kawahara, S. Kameda, T. Iwata, Y. Ishihara, M. Ishiguro, H. Ikeda, S. Hosoda, R. Honda, C. Honda, Y. Hitomi, N. Hirata, N. Hirata, T. Hayashi, M. Hayakawa, K. Hatakeda, S. Furuya, R. Fukai, A. Fujii, Y. Cho, M. Arakawa, M. Abe, S. Watanabe and Y. Tsuda, 22 September 2022, Science.
DOI: 10.1126/science.abn8671