A Long‐Lived Planetesimal Dynamo Powered by Core Crystallization

The existence of numerous iron meteorite groups indicates that some planetesimals underwent melting led to metal-silicate segregation, sometimes producing metallic cores. Meteorite paleomagnetic records suggest crystallization these cores generated dynamo magnetic fields. Here we describe the history partially differentiated IIE parent body. This is first planetesimal for which have a time-resolved record constrained by 40Ar/39Ar chronometry spanning several tens million years (Ma). We find core body dynamo, likely powered crystallization, starting before 78 ± 13 Ma after solar system formation and lasting at least 80 Ma. Such extended suggests composed substantial fraction ( 13%–19% core-to-body radius ratio depending on body’s radius), indicating efficient within planetesimals.