Solar System’s earliest solids as tracers of the accretion region of Ryugu and Ivuna-type carbonaceous chondrites

Samples from the carbonaceous asteroid Ryugu and CI (Ivuna-type) chondrites are dominated by low-temperature, aqueously formed secondary minerals, with rare occurrences of anhydrous primary minerals that formed in the high-temperature region of the solar protoplanetary disk. Here, we show that small (<a few tens of micrometers) Ca-Al-rich inclusions (CAIs) in Ryugu and Ivuna formed within ~0.2 Ma of the Solar System’s birth. These CAIs exhibit mineralogical, O-isotopic, and chronological similarities to CAIs in ordinary and other carbonaceous chondrites, indicating their ubiquitous presence across chondrites. In contrast, larger (>submillimeter) CAIs, commonly found in other carbonaceous chondrites and thought to have been retained via pressure bump(s) in the disk, are absent in Ryugu and CI chondrites. This absence implies that their parent planetesimals formed at a greater heliocentric distance, beyond the influence of a pressure bump created by proto-Jupiter, accreting only small CAIs that evaded radial drift toward the Sun. The parent planetesimals of Ryugu and CI chondrites may have formed beyond a pressure bump created by proto-Jupiter, based on the absence of large CAIs and the ubiquitous presence.