2025-08-25 北海道大学
探査機「オサイリスレックス」により撮影された小惑星「ベヌー」の写真（左）と、「ベヌー」に含まれる高温環境で生成された鉱物の電子顕微鏡写真（右）。鉱物は北海道大学にて研究されたもの。 （NASA, Barnes, Nguyen et al. 2025）
＜関連情報＞
- https://www.hokudai.ac.jp/news/2025/08/nasa-1.html
- https://www.hokudai.ac.jp/news/pdf/250825_pr.pdf
- https://www.nature.com/articles/s41550-025-02631-6
ベヌーの母天体に集積した物質の多様性と起源 The variety and origin of materials accreted by Bennu’s parent asteroid
J. J. Barnes,A. N. Nguyen,F. A. J. Abernethy,K. Bajo,D. V. Bekaert,E. Bloch,G. A. Brennecka,H. Busemann,J. S. Cowpe,S. A. Crowther,M. Ek,L. J. Fawcett,M. A. Fehr,I. A. Franchi,E. Füri,J. D. Gilmour,M. M. Grady,R. C. Greenwood,P. Haenecour,N. Kawasaki,P. Koefoed,D. Krietsch,L. Le,K. M. Liszewska,… D. S. Lauretta
Nature Astronomy Published:22 August 2025
DOI:https://doi.org/10.1038/s41550-025-02631-6
Abstract
The first bodies to form in the Solar System acquired their materials from stars, the presolar molecular cloud and the protoplanetary disk. Asteroids that have not undergone planetary differentiation retain evidence of these primary accreted materials. However, geologic processes such as hydrothermal alteration can dramatically change their bulk mineralogy, isotopic compositions and chemistry. Here we analyse the elemental and isotopic compositions of samples from asteroid Bennu to uncover the sources and types of material accreted by its parent body. We show that some primary accreted materials escaped the extensive aqueous alteration that occurred on the parent asteroid, including presolar grains from ancient stars, organic matter from the outer Solar System or molecular cloud, refractory solids that formed close to the Sun, and dust enriched in neutron-rich Ti isotopes. We find Bennu to be richer in isotopically anomalous organic matter, anhydrous silicates, and light isotopes of K and Zn than its closest compositional counterparts, asteroid Ryugu and Ivuna-type (CI) carbonaceous chondrite meteorites. We propose that the parent bodies of Bennu, Ryugu and CI chondrites formed from a common but spatially and/or temporally heterogeneous reservoir of materials in the outer protoplanetary disk.
