Perspectives on Magnetic Reconnection from MMS

Abstract:

Advances in plasma physics in the Earth’s magnetosphere over the past five years result in large part from the implementation of electron-scale measurements from four closely-spaced probes by the NASA Magnetospheric Multiscale (MMS) mission. Of equal importance is the rapid advances in kinetic plasma simulations, which allow full 3D treatments with sufficient numbers of electrons to match the MMS measurement cadence and expose turbulent effects. These new capabilities are focused primarily, although not exclusively, on magnetic reconnection in the boundary regions of the magnetosphere, most notably the dayside magnetopause and the neutral sheet in the magnetic tail. On the day side the predictions of asymmetric reconnection and effects of guide fields are tested and, in many cases, resolved. Tail events provide detailed studies of symmetric reconnection and energetic particle acceleration. In addition to providing our first look at reconnection in space at the electron scale, MMS reveals a much more ubiquitous nature of reconnection than was previously supposed. Reconnection is found in bow shocks, Kelvin-Helmholtz vortices, magnetic flux ropes, flux transfer events, and near-tail dipolarization fronts. Our overall perspective is that magnetic reconnection is much more widespread and important to magnetospheric dynamics than we ever imagined. The detailed physics of reconnection is also being revised as we go from testing predictions of theory and modeling, many of which are turning out to be correct, to explaining new and unanticipated measurements. It is indeed an exciting time for research on magnetospheric physics in general and on magnetic reconnection in particular.