Heliophysics Science Division
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Search for Thermalization of Na+ Pickup Ions in Mercury's Magnetosheath and Magnetosphere via Observation and Hybrid Simulation

Scott Boardsen (UMBC)

In previous studies it has been suggested that the incorporation of Na+ pickup ions into Mercury's magnetosphere could have a significant impact on various magnetospheric processes. Test particle simulations indicate that freshly created Na+ ions are rapidly energized and lost from the system. In order to incorporate these ions into the bulk magnetospheric plasma they must be thermalized. A recent study that used linear theory suggests that the wavelengths of electromagnetic ion cyclotron waves may be to large and may not grow to sufficient amplitudes to thermalize these ions and concluded that global thermalization of these ions is not possible. However, under certain solar wind and IMF conditions such thermalization might take place in limited regions of Mercury's magnetosphere, primarily in the sub-solar magnetosheath. Due the small scale size of Mercury's magnetosphere compared to the gyro-radii of these heavy ions and their associated wave modes, hybrid simulation with a kinetic treatment for the ions and a fluid treatment for the electrons may be the only way to study if thermalization of Na+ can occur. We will review our observational study that attempted to search for wave signatures of thermalization in the Mariner-10 data, and give preliminary results of a hybrid simulation that incorporates the Na+ pickup ions in its kinetic treatment will be presented.