2026-07-23 北海道大学,京都大学,海洋研究開発機構
小惑星「ベヌー」から見つかった難揮発性包有物の例。そのうち一つ（左）は、太陽系誕生直後の約45億6,730万年前に形成されたことが判明。データはMg(赤)―Ca(緑)―Al(青)の合成X線元素マップ。スケールバーは0.01ミリメートル。（©Kawasaki et al. 2026）
＜関連情報＞
- https://www.hokudai.ac.jp/news/2026/07/post-2365.html
- https://www.nature.com/articles/s41467-026-73868-6
小惑星ベヌー試料中の難揮発性包有物が示す外側太陽系での集積 Refractory inclusions in Bennu samples indicative of outer Solar System accretion
Noriyuki Kawasaki,Toru Matsumoto,Sota Arakawa,Naoya Sakamoto,Ken-ichi Bajo,Sara S. Russell,Jessica J. Barnes,Ann N. Nguyen,Timothy J. McCoy,Pierre Haenecour,Hisayoshi Yurimoto,Harold C. Connolly Jr. & Dante S. Lauretta
Nature Communications Published:18 July 2026
DOI:https://doi.org/10.1038/s41467-026-73868-6 Unedited version
Abstract
NASA’s OSIRIS-REx mission returned material from the carbonaceous asteroid Bennu, which is dominated by aqueous-alteration products but preserves rare high-temperature components. Here we present an integrated petrographic, oxygen-isotopic and 26Al–26Mg chronological characterization of refractory inclusions in Bennu samples. All identified inclusions are small (<~100 µm) and commonly preserve mineralogical evidence of in situ aqueous alteration, indicating incorporation into Bennu’s parent body prior to hydration. Their mineralogical characteristics and oxygen-isotopic and 26Al–26Mg systematics demonstrate formation during the earliest stage of Solar System evolution and genetic affinity with refractory inclusions in asteroid Ryugu samples and chondritic meteorites. The shared refractory-inclusion signatures across diverse chondritic materials are consistent with widespread outward transport and mixing of early-formed inner-disk solids. In Bennu samples analyzed thus far, large (>submillimeter) refractory inclusions are absent, in contrast to most carbonaceous chondrites. This size distribution implies that Bennu’s constituents accreted in the outer Solar System beyond the pressure bump associated with proto-Jupiter, which effectively filtered distinct dust populations.
