Meteoritic Evidence for the Infall of Large Interstellar Dust Aggregates during the Formation of the Solar System

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Abstract
The presence of the short-lived radionuclide 26Al in some of the refractory inclusions of chondritic meteorites but not in others appears to mean that the substance of the 26Al-free inclusions was brought together in the presolar interstellar medium, before the astrophysical event occurred that synthesized solar system 26Al. The 26Al-free inclusions can be understood as evaporation residues that formed from presolar dust aggregations when they were intensely heated by gas drag as they fell into the solar nebula during the collapse phase of solar system formation. The inclusions containing 26Al were formed from dust that had been seeded with that nuclide prior to aggregation and thermal processing.