Prolonged early migration of dust from the inner Solar System to the comet-forming region

Abstract

The most abundant group of meteorites currently falling to Earth, ordinary chondrites, originate from S-type (Si-rich) asteroids and are thought to have originated in the inner Solar System. These asteroids typically underwent only minor aqueous alteration but experienced varying degrees of thermal metamorphism that altered their primary compositions and textures. However, some rare members remain unaltered and retain the pristine compositions they obtained in the protoplanetary disk prior to accretion of their parent asteroids. In contrast, comets formed in the icy reaches of the outer Solar System. Here we report on silicate minerals in pristine ordinary chondrites that are compositionally distinct from those in all other known chondrites but show similarities to those found in comet samples returned from Comet Wild 2 by NASA's Stardust mission and those sourced from an unknown number of comets represented by interplanetary dusty particles. The identification of this material suggests that comets may have formed from diverse far-flung Solar System materials, including grains that migrated from the inner Solar System to the comet-forming region between ∼1 Myr and potentially ⪆3 Myr after the first Solar System solids formed. This finding suggests that migration from the inner to the outer Solar System lasted for millions of years and that comets are composed of residual materials from the entire early Solar System.