Magnetic Reconnection: What do We Know Now, and What Remains Unsolved

Magnetic reconnection (MR) is one of the most important transport and energy-release processes in collisionless plasmas.  Although governed by highly localized kinetic physics, MR enables system-scale changes, often involving explosive conversion ofstored magnetic energy into particle energy. MR powers such diverse plasma phenomena as solar and stellar flares, geomagnetic storms, and the aurora, and underlies many of the deleterious effects collectively referred to as space weather. Magnetic reconnection therefore constitutes an important and accessible example of a fundamentally multiscale physical process.

While the global consequences of magnetic reconnection have been understood at a conceptual level for some time, the detailed physics governing its operation remained elusive until recently. The advent of the Magnetospheric Multiscale (MMS) mission, which has provided—and continues to provide—unprecedented in situ measurements, has supplied both new empirical insight and critical ground truth for theory and numerical modeling.

MMS has largely resolved how MR operates at its core: the small spatial region that enables large-scale plasma dynamics. More recent results have begun to illuminate the mechanisms of energy conversion and the physical coupling between this central region and its surrounding environment. This presentation will summarize the current understanding of MR and highlight emerging research directions that follow from these recent advances.