The abundant phyllosilicate and carbonate minerals characterizing most of the returned particles from asteroid Ryugu suggest a history of extensive aqueous alteration on its parent body, similar to the rare mineralogically altered, but chemically primitive, CI (Ivuna-type) chondrite meteorites. Particle C0009 differs mineralogically from other Ryugu particles examined so far by containing anhydrous silicates at a level of ~0.5 vol%, and thus can help shed light on the unaltered original materials that constituted Ryugu’s protolith. In situ oxygen isotope measurements of the most Mg-rich olivine and pyroxene in C0009 reveal two populations of Δ¹⁷O: −25‰ to −15‰ and −8‰ to −3‰. The former and the latter populations correlate well with silicate morphologies similar to those seen in amoeboid olivine aggregates and chondrule phenocrysts, respectively, both of which are abundant in less aqueously altered carbonaceous chondrites. This result also highlights the presence of olivine with Δ¹⁷O close to the solar value in either a CI chondrite or an asteroid with CI-chondrite characteristics, and provides strong evidence that amoeboid olivine aggregates and Mg-rich chondrules accreted into Ryugu’s protolith. Our data also raise the possibility that the protoliths of CI and other carbonaceous chondrites incorporated similar anhydrous silicates.

丰富的页硅酸盐和碳酸盐矿物是小行星 Ryugu 大部分返回颗粒的特征，这表明其母体有广泛的水蚀变历史，类似于罕见的矿物学变质但化学上原始的 CI（Ivuna 型）球粒陨石。粒子 C0009 在矿物学上不同于迄今为止检测的其他 Ryugu 粒子，因为它含有约 0.5 vol% 的无水硅酸盐，因此有助于阐明构成 Ryugu 原石的未改变的原始材料。C0009 中最富含镁的橄榄石和辉石的原位氧同位素测量揭示了两个 Δ ^17种群O：-25‰ 至 -15‰ 和 -8‰ 至 -3‰。前者和后者的种群与硅酸盐形态的相关性很好，类似于分别在变形虫橄榄石聚集体和球粒斑晶中看到的那些，这两种形态在较少水性改变的碳质球粒陨石中都很丰富。该结果还强调了在 CI 球粒陨石或具有 CI 球粒陨石特征的小行星中存在 Δ ¹⁷ O 接近太阳值的橄榄石，并提供了强有力的证据表明变形虫橄榄石聚集体和富含镁的球粒附着在 Ryugu 的原石中。我们的数据还提出了 CI 和其他碳质球粒陨石的原石包含类似无水硅酸盐的可能性。