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Origin of the CC-NC isotopic dichotomy in early planetesimals (iron meteorite parent bodies)

The isotopic dichotomy between carbonaceous (CC) and non-carbonaceous (NC) chondrites has been shown to exist also among iron meteorites[1], whose parent bodies are the first planetesimals that formed in the Solar System, within 1 My of CAIs. The distinct highly-siderophile-element concentration in CC and NC iron meteorites indicates that the parent bodies of the former were significantly more oxidized than those of the latter. The isotopic and oxidation dichotomies suggest that the earliest planetesimals in the solar system formed at two distinct sites, one of which richer in water than the other. In this work[2], by modeling the evolution of a disk with ongoing accretion of material from the collapsing molecular cloud, we show that planetesimal formation via the streaming instability may have been triggered within the first 0.5 million years by dust pile-up at both the snowline (at ~5 au) and the silicate sublimation line (at ~1 au). Particle concentration at ~1 au is due to the early outward radial motion of gas and is assisted by the sublimation and recondensation of silicates. Our results indicate that, although the planetesimals at the two locations formed about contemporaneously, those at the snowline accreted a large fraction of their mass (~60%) from materials delivered to the disk in the first few 10