Elemental and isotopic variability in solar system materials by mixing and processing of primordial disk reservoirs

TL;DR

This study investigates the isotopic variability in solar system materials, revealing that planetary anomalies result from mixing of distinct primordial reservoirs inherited from the molecular cloud, shaped by nebular processing.

Contribution

It identifies the main nebular reservoirs responsible for planetary isotopic variations and links these to inherited heterogeneity from the solar system's parental cloud.

Findings

Nebular isotopic heterogeneity is largely decoupled from planetary-scale anomalies.

Mixing of non-carbonaceous and a CAI-like reservoir explains isotopic differences.

Inherited heterogeneity of the molecular cloud influenced nebular reservoir composition.

Abstract

Isotope anomalies among planetary bodies provide key constraints on planetary genetics and the Solar System's dynamical evolution. However, to unlock the full potential of these anomalies for constraining the processing, mixing, and transport of material in the disk it is essential to identify the main components responsible for producing planetary-scale isotope variations, and to investigate how they relate to the isotopic heterogeneity inherited from the Solar System's parental molecular cloud. To address these issues we measured the Ti and Sr isotopic compositions of Ca,Al-rich inclusions (CAIs) from the Allende CV3 chondrite, as well as acid leachates and an insoluble residue from the Murchison CM2 chondrite, and combine these results with literature data for presolar grains, hibonites, chondrules, and bulk meteorites. Our analysis reveals that the mineral-scale nebular isotopic heterogeneity as sampled by leachates and presolar grains is largely decoupled from the planetary-scale isotope anomalies. Combining isotope anomaly data for a large number of elements reveals that the difference between non-carbonaceous (NC) and carbonaceous (CC) meteorites is the product of mixing between NC material and a nebular reservoir (termed IC) whose isotopic composition is similar to that of CAIs, but whose chemical composition is similar to bulk chondrites. In our preferred model, the distinct isotopic compositions of these two nebular reservoirs reflect an inherited heterogeneity of the solar system's parental molecular cloud core, which therefore has never been fully homogenized during collapse. Planetary-scale isotopic anomalies are thus caused by variable mixing of isotopically distinct primordial disk reservoirs, the selective processing of these reservoirs in different nebular environments, and the heterogeneous distribution of the thereby forming nebular products.