Abstract

In this two-part talk, I review how key unsolved problems in our understanding of the magnetism of the ancient moon and solar nebula can be addressed with paleomagnetic measurements. Remanent magnetization in lunar rocks has long been hypothesized to be the product of a core dynamo. However, the paleofield’s apparent high intensity and longevity are major challenges to current theory. Two key difficulties are that the paleofield’s intensity has been poorly constrained and its direction has been essentially unknown. I describe three key new types of ongoing paleomagnetic measurements that address these issues. First, controlled atmosphere thermal demagnetization is enabling some of the first accurate lunar paleointensity measurements. Second, paleointensities are being measured for young samples to constrain the field’s lifetime. Finally, constraints on the field’s paleodirection are being derived from bedrock samples. The data collectively support the existence of an early (>~3.5 Ga) dynamo with a fluctuating intensity, perhaps powered by an unusually energetic mechanism like precession, followed by a weaker long-lived dynamo perhaps powered by core crystallization. The paleodirectional data are consistent with but do not require a Moon-centric axial dipole geometry like that of the Earth. A key stage in planet formation is the evolution of a gaseous and magnetized solar nebula. However, the intensity and lifetime of the nebular field and the history of mass transport in the early solar system have been poorly constrained. Here we present analyses of the remanent magnetization in meteorites demonstrating that an approximately Earth-strength nebular magnetic field existed throughout the inner solar system (