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Abstract

A key cosmochemical discovery is the existence of a disk gradient in abundance of supernovea (SN) nuclides in planetary material with orbital distance. Volatile-poor inner Solar System bodies record SN depletions whereas water-rich outer Solar System objects show enrichments. As this nucleosynthetic variability can be used to trace the source of disk material that accretes to planets, understanding the mechanism responsible for this spatial variability is a major unresolved impediment. Here, we explore the hypothesis that interstellar ices were an important carrier of SN nuclides by conducting a search for the signature of SN nuclides in various types of chondrite meteorites, including carbonaceous and non-carbonaceous chondrites. Chondrites are known to have accreted variable amounts of ices as indicated by the pervasive aqueous alteration experienced by these meteorites while on their parent bodies. Thus, strategically-designed step leaching experiments using mild acids aimed at exclusively dissolving the labile alteration minerals can be used to determine the isotopic signal of the ice component. We focus on the refractory and immobile element zirconium, which owe its nucleosynthesis to both the s– and r–process. In particular, the neutron-rich 96Zr nuclide is overproduced in the explosive He-burning shells of core-collapse supernovae. Thus, 96Zr enrichments preserved in meteoritic components is a hallmark of a supernova signature. The isotopic compositon of the leachates returns highly anomalous signals characterized by variable and extreme enrichments in the neutron-rich 96Zr nuclide. These results are consistent with the ices being the main carrier of anomalous Zr characterized by large 96Zr excesses. By comparing the Zr isotopic composition of the leaches with that of bulk planetary material, we show that the Solar System’s Zr isotopic variability can be ascribed to admixing of variable amounts of interstellar ices to an ice-free rock endmember. These results have important implications for the origin of the Solar System nucleosynthetic variability, the solar ice/rock ratio and planet formation mechanisms. Finally, our data support models suggesting that a significant fraction of the primary reservoir of volatile-rich ices in the early Solar System was direct inherited from the molecular cloud as opposed to formed in the protoplanetary disk.