The parent bodies of Ryugu and Ivuna formed before those of other carbonaceous chondrites.

Kawasaki, Noriyuki; Nagashima, Kazuhide; Sakamoto, Naoya; Fujiya, Wataru; Arakawa, Sota; Bajo, Ken-Ichi; Kita, Noriko T; Kitajima, Kouki et al. · Science · 2026

basic_science · Level V

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Abstract

Most carbonaceous chondrite (CC) meteorites contain abundant chondrules, millimeter-scale spherical inclusions of previously molten material. Ivuna-type carbonaceous chondrites (CIs) do not contain chondrules, nor do samples of the carbonaceous asteroid Ryugu. CIs and Ryugu share isotopic properties distinct from those of other CCs, implying that their parent bodies formed at a different time or place than those of other CCs. We applied manganese-chromium dating and oxygen isotope thermometry to Ryugu and Ivuna samples. The results indicate that the parent bodies of Ryugu and Ivuna formed less than 2 million years after the beginning of Solar System formation-before the majority of chondrules in CCs and the parent bodies of other CCs formed. This implies that Ryugu and CIs are remnants of an earlier generation of carbonaceous planetesimals.