Advances in the Study of Collisionless Plasma Turbulence in the Era of NASA's Magnetospheric Multiscale Mission*

Many plasmas throughout the Universe contain complex turbulent dynamics that serve to facilitate plasma heating and particle energy exchange, generate structure that is observed in the plasma, and mix different plasma populations. The study of turbulence is a key challenge in the field of plasma physics and the detailed measurements of large plasma systems that can be made with in situ spacecraft measurements of near-Earth space provide an exciting opportunity to directly examine the fundamental physics of plasma turbulence. Launched in 2015, NASA’s Magnetospheric Multiscale (MMS) mission is a four-spacecraft formation of Earth-orbiting spacecraft, capable of measuring high-resolution 3D particle distribution functions, electromagnetic fields, and spatial gradients at scales approaching the characteristic scales of the electrons. This talk will give an overview of several unique studies of plasma turbulence that have been enabled by MMS measurements in the region of shocked solar wind plasma downstream of Earth’s bow shock, known as the magnetosheath. In the first set of studies, multipoint MMS observations are used to directly measure the linear and nonlinear contributions to generalised Ohm’s law, providing insight into the nature of the dynamics that give rise to turbulent electric fields in a collisionless plasma from fluid to electron scales. In the second set of studies, high-resolution measurements from MMS are used to systematically identify and examine the significance of small-scale magnetic reconnection events embedded within the turbulent plasma. Both these studies provide new advances to our understanding of how turbulent dynamics and energy dissipation are impacted by the kinetic-scale effects that come into play as the fluid approximation breaks down in the nearly collisionless plasmas that are often found in space.