Physics & Astronomy Benjamin Weiss '95, MIT: "History of the solar nebula from meteorite and cometary paleomagnetism"

Theoretical studies have long suggested that magnetic fields played a central role in the formation of planetary systems by mediating angular momentum and mass transport during the protoplanetary disk stage. In particular, magnetic fields are thought to have driven stellar accretion, influenced the accretion of planetesimals, and may be associated with processes that formed the first solar system solids. However, until recently the existence and intensity of the nebular field have been unknown. Here we present analyses of the remanent magnetization in several meteorite groups demonstrating that an approximately Earth-strength nebular magnetic field existed in the inner solar system (<3 AU) during the first 3 million years after solar system formation. The strong intensity of the field supports the hypothesis that magnetic fields played a fundamental role in planet formation. Furthermore, measurements from the Philae lander on the surface comet 67P Churyumov-Gerasimenko suggest that the outer solar system (i.e., 14-45 AU) field was near-zero at the same time. Our measurements of the remanent magnetization in younger meteorites indicate that the inner solar system field then declined to near-zero by ~4 million years after solar system formation, implying that the solar nebula had dispersed by this time. This supports the hypothesis that giant planets form by a two-stage process involving formation of a rock-ice core followed by runaway gas accretion.