Chondrule-like objects and CAIs in asteroid Ryugu: earlier generations of chondrules

Abstract Chondrule-like objects and Ca-Al-rich inclusions (CAIs) are discovered in the retuned samples from asteroid Ryugu. Three chondrule-like objects, which are 16O-rich and -poor with D17O (= d17O – 0.52 × d18O) values of ~ − 23‰ and ~ − 3‰, are dominated by Mg-rich olivine, resembling what proposed as earlier generations of chondrules. The 16O-rich objects are likely to be melted amoeboid olivine aggregates that escaped from incorporation into 16O-poor chondrule precursor dust. Two CAIs composed of spinel, hibonite, and perovskite are 16O-rich with D17O of ~ − 23‰ and possibly as old as the oldest CAIs. The chondrule-like objects and CAIs (< 30 µm) are as small as those from comets, suggesting radial transport favoring smaller objects from the inner solar nebula to the formation location of the Ryugu original parent body, which is farther from the Sun and scarce in chondrules. The transported objects may have been mostly destroyed during aqueous alteration.