Evolution of the Solar Nebula. VIII. Spatial and Temporal Heterogeneity of Short-Lived Radioisotopes and Stable Oxygen Isotopes

Abstract

Isotopic abundances of short-lived radionuclides such as 26Al provide the most precise chronometers of events in the early solar system, provided that they were initially homogeneously distributed. On the other hand, the abundances of the three stable isotopes of oxygen in primitive meteorites show a mass-independent fractionation that survived homogenization in the solar nebula. As as result of this and other cosmochemical evidence, the degree of spatial heterogeneity of isotopes in the solar nebula has long been a puzzle. We show here that based on hydrodynamical models of the mixing and transport of isotopic anomalies formed at, or injected onto, the surface of the solar nebula, initially high levels of isotopic spatial heterogeneity are expected to fall to steady state levels (~10%) low enough to validate the use of 26Al for chronometry, but high enough to preserve the evidence for mass-independent fractionation of oxygen isotopes. The solution to this puzzle relies on the mixing being accomplished by the chaotic fluid motions in a marginally gravitationally unstable disk, as seems to be required for the formation of gas giant planets and by the inability of alternative physical processes to drive large-scale mixing and transport in the planet-forming midplane of the solar nebula. Such a disk is also capable of large-scale outward transport of the thermally annealed dust grains found in comets, and of driving the shock fronts that appear to be responsible for much of the thermal processing of the components of primitive meteorites, creating a self-consistent picture of the basic physical processes shaping the early solar nebula.

25 pages, 10 figures

References in corpus (5)

• The nucleosynthesis of Al26 and Fe60 in solar metallicity stars extending in mass from 11 to 120 Msun: the hydrostatic and explosive contributions
• The Evolution of the Water Distribution in a Viscous Protoplanetary Disk
• The Irradiation Origin of Beryllium Radioisotopes and Other Short-lived Radionuclides
• Turbulent Mixing in the Outer Solar Nebula
• Turbulence driven diffusion in protoplanetary disks - chemical effects in the outer disk

Cited by in corpus (13)

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• Extreme 54Cr-rich nano-oxides in the CI chondrite Orgueil -Implication for a late supernova injection into the Solar System
• Mixing in the Solar Nebula: Implications for Isotopic Heterogeneity and Large-Scale Transport of Refractory Grains
• Triggering Collapse of the Presolar Dense Cloud Core and Injecting Short-Lived Radioisotopes with a Shock Wave. I. Varied Shock Speeds
• Isotopic enrichment of forming planetary systems from supernova pollution
• Fingerprints of the protosolar cloud collapse in the Solar System II: Nucleosynthetic anomalies in meteorites
• Cosmochemical Consequences of Particle Trajectories During FU Orionis Outbursts by the Early Sun
• Evolution of the Solar Nebula. IX. Gradients in the Spatial Heterogeneity of the Short-Lived Radioisotopes ${}^{60}$Fe and ${}^{26}$Al and the Stable Oxygen Isotopes
• Mixing and Transport of Short-Lived and Stable Isotopes and Refractory Grains in Protoplanetary Disks
• The Accretion Disc Dynamo in the Solar Nebula
• Asteroids and Comets
• Microscopic folding model analysis of the radiative $(n,\gamma )$ reactions near the $Z=28$ shell-closure and the weak s-process