Puzzles in Planetary Dynamos: Implications for Planetary Interiors

Intrinsic magnetic fields were once commonplace across our Solar System, and many planetary bodies have sustained active dynamos to the present day. The nature and behavior of these dynamos vary widely, however, reflecting the diverse internal conditions of planets as summarized in this review. For the terrestrial planets, the existence of active dynamos and/or ancient remanent magnetization recorded in crustal rocks, or lack thereof, lead to questions about their timing and power sources. Paleomagnetic studies reveal that many small bodies in the Solar System exhibit remanent magnetization, often attributed to ancient core dynamos with little known about the fluid dynamics. For the gas giants, their dipole-dominated magnetic fields and internal structures are relatively well-characterized, with dilute cores that are not centrally concentrated and other stable layers that likely affect the dynamo in ways that are not yet understood. For the ice giants, their multipolar magnetic fields and internal structures are unusual yet poorly constrained, to the extent that even the water-to-rock ratio is not well-known. Through adoption of a broader comparative planetology approach, the study of dynamos in exoplanets and cool stars enriches our understanding of dynamo theories. ▪ Planetary dynamos exhibit diverse magnetic fields shaped by their distinct physical and chemical conditions. ▪ The study of planets and stars connects planetary science, geophysics, and astrophysics, revealing shared dynamo processes. ▪ While significant progress has been made in understanding planetary and stellar magnetic fields, many puzzles still persist.