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Koronis asteroid dust within Antarctic ice

¹ Impact and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, UK, and Mineralogy Department, The Natural History Museum, Cromwell Road, London SW7 5BT, UK

Here I report the first discovery of large numbers of ordinary chondrite–derived micro-meteorites (MMs) recovered from Antarctic ice. Ordinary chondrite–derived MMs comprise 70% coarse-grained igneous particles and are identified on the basis of their distribution of petrologic types, accessory mineralogy, and minor element compositions, all of which are very similar to those of millimeter-sized igneous objects known as chondrules, from ordinary chondrites, and largely distinct from those of other meteorite groups. The majority of ordinary chondrite–derived MMs are unequilibrated materials; however, 15% are equilibrated, indicating parent body metamorphism, and have compositions consistent with both H (high iron) and L (low iron) chondrites. The total abundance of ordinary chondrite–derived MMs of ~18% is similar to predictions by numerical calculations for the abundance of dust generated by the recent breakup of the Karin group asteroids of the Koronis asteroid family, suggesting that these asteroids are the main source of the particles. These MMs represent the first to be associated with a known asteroid and imply that the Karin group progenitor asteroid was a rubble-pile asteroid that sampled different depths within the original internally metamorphosed Koronis parent body.

Key Words: micrometeorites • meteorites • asteroids • ordinary chondrites

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