Chondrules reveal large-scale outward transport of inner Solar System materials in the protoplanetary disk.

Dynamic models of the protoplanetary disk indicate there should be large-scale material transport in and out of the inner Solar System, but direct evidence for such transport is scarce. Here we show that the ε ⁵⁰ Ti-ε ⁵⁴ Cr-Δ ¹⁷ O systematics of large individual chondrules, which typically formed 2 to 3 My after the formation of the first solids in the Solar System, indicate certain meteorites (CV and CK chondrites) that formed in the outer Solar System accreted an assortment of both inner and outer Solar System materials, as well as material previously unidentified through the analysis of bulk meteorites. Mixing with primordial refractory components reveals a "missing reservoir" that bridges the gap between inner and outer Solar System materials. We also observe chondrules with positive ε ⁵⁰ Ti and ε ⁵⁴ Cr plot with a constant offset below the primitive chondrule mineral line (PCM), indicating that they are on the slope ∼1.0 in the oxygen three-isotope diagram. In contrast, chondrules with negative ε ⁵⁰ Ti and ε ⁵⁴ Cr increasingly deviate above from PCM line with increasing δ ¹⁸ O, suggesting that they are on a mixing trend with an ordinary chondrite-like isotope reservoir. Furthermore, the Δ ¹⁷ O-Mg# systematics of these chondrules indicate they formed in environments characterized by distinct abundances of dust and H ₂ O ice. We posit that large-scale outward transport of nominally inner Solar System materials most likely occurred along the midplane associated with a viscously evolving disk and that CV and CK chondrules formed in local regions of enhanced gas pressure and dust density created by the formation of Jupiter.
Competing Interests: The authors declare no competing interest.
(Copyright © 2020 the Author(s). Published by PNAS.)