Mercury's Plasma Mantle during Solar Wind Dynamical Pressure Enhancements
Résumé
Because of the weak planetary magnetic field as well as proximity to the Sun, the magnetosphere of Mercury is very dynamical and at times subjected to prominent compression. Recent observations from MESSENGER reveal that during events of enhanced solar wind dynamical pressure, the subsolar magnetopause may actually be pushed until the immediate vicinity of the planet surface. Using three-dimensional single-particle simulations, we examine the dynamics of solar wind originating protons during such events. We show that these impulsive events can lead to substantial (several hundreds of eVs or a few keVs) H energization in the plasma mantle. Unlike ions with large mass-to-charge ratios (e.g., Na of planetary origin), H are transported adiabatically during these events, their energization being due to the ExB convection surge. MESSENGER observations of the plasma mantle show repeated evidences of such a transient H energization which may follow from the variable character of Mercury's magnetosphere.