Kinetic-Scale Magnetic Fluctuations in the Near-Mercury Space Environment

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to address several critical questions regarding the formation and evolution of the terrestrial planets, including fundamental processes controlling the dynamics of Mercury's magnetosphere. In this talk, we present statistical properties of the magnetic field fluctuations recorded by the Magnetometer obnoard MESSENGER during its three flybys through the near-Mercury space environment prior to orbit insertion. We apply turbulent analysis tools as a means of characterizing ion kinetic scales in different plasma structures surrounding Mercury. Our methodology is based on the existence of scaling crossover separating MHD and ion kinetic regimes of magnetic fluctuations. By identifying this crossover in the temporal domain and mapping the results to the wave-number space using predicted values of flow velocity, we evaluate the ion gyro radius and temperature in several locations in the magnetosphere. These measurements are compared with earlier theoretical estimates and simulation results. We show that scaling regimes of magnetic fluctuations vary greatly in Mercury's foreshock, magnetosheath, and the magnetosphere. The observed regimes involve contributions from a variety of non-random processes and structures, including boundary layers, rotating flows, and propagating waves. Our analysis suggests that ion kinetic turbulence is present in all plasma structures at Mercury and is the leading source of stochastic variability inside the magnetopause up to the largest resolvable scales imposed by a data nonstationarity.