IIE Iron Meteorites Suggest a Single Parent Asteroid with a Core Dynamo and Layers of Chondritic and Achondritic Material

Image credit: Maurel et al., 2020

Most meteorites in our collection are materials derived from the main asteroid belt. The traditional classification of these meteorites suggests that they come from either primitive, undifferentiated asteroids that have never been melted (i.e., chondrites) or differentiated asteroids that were partially or completely melted (i.e., achondrites). Radiometric dating of differentiated meteorites, in combination with observations of exoplanetary systems, suggests that planetary formation and differentiation was a rapid process at the beginning of the solar system. In contrast, most undifferentiated (chondritic) meteorites have radiometric ages indicating that they formed later than their achondritic counterparts, which implies that the known chondrites do not necessarily represent the precursors of the achondrites.

However, a recent study by a team led by Clara Maurel from the Massachusetts Institute of Technology suggests an alternative view. The scientists analyzed a specific type of meteorite, the IIE irons. These meteorites contain a variety of fragments that appear to represent both differentiated and undifferentiated bodies. The team’s paleomagnetic study suggests that the parent asteroid of these meteorites had a dynamo, which requires a molten metallic core indicative of a differentiated body. To account for all of the observed properties of these samples, including the presence of undifferentiated material, the authors suggest that the parent asteroid of IIE iron meteorites had a multilayered onion-shell structure with a liquid metallic core, a differentiated silicate mantle, and outer layers of undifferentiated materials. Subsequent impacts into this asteroid resulted in excavation of material and/or complete disruption, mixing fragments from the different layers from the full range of differentiation stages to create the IIE iron meteorites. These results suggest that the traditional meteorite classification scheme may be misleading and that samples from the two different classes of meteorites, chondritic and achondritic meteorites, could in fact originate from the same parent body. READ MORE