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Don Brownlee Colloquium Abstract (Feb 22, 2017)

What Samples of a Comet Tell Us About the Origin of the Solar System

The return of comet samples collected by the NASA Stardust mission provided a unique opportunity to do detailed laboratory analyses on materials that formed small icy bodies at the edge of the solar system.  Unexpectedly, isotopically anomalous presolar grains were found to be only a trace component. The comet does however contain a remarkable of array of materials that are close analogs to materials found in primitive meteorites such as fragments of chondrules and calcium aluminum inclusions, the oldest solar system solids.  The results suggest that this comet is a mix of organics and ices that formed in cold environments along with rocky components that formed at incandescent temperatures, presumably in inner solar system environments.  The results provide "ground truth" evidence for large-scale radial movement of solid grains in the early solar system.  Although the comet contains "meteoritic materials", it does not appear to closely match any class of meteorite and the comet solids appear to be a mix of components from a broad range of inner solar system environments. A major difference between comets and asteroids may be that comet solids are mixes of distantly made materials while asteroids contain major amounts of regionally made materials that give asteroids and their meteorites their distinctive properties. A prediction from this work is that most icy planetesimals in the early solar system may typically have contained a similar standard mix of nebular solids made in distant locales and transported outwards.