Particle Acceleration in Mercury’s Magnetosphere

This paper is devoted to the problem of particle acceleration in the closest to the Sun Hermean magnetosphere. We discuss few available observations of energetic particles in Mercury environment made by Mariner-10 in 1974–1975 during Mercury flyby’s and by Helios in 1979 upstream of the Hermean bow shock. Typically ions are non-adiabatic in a very dynamic and compact Mercury magnetosphere, so one may expect that particle acceleration will be very effective. However, it works perfectly for electrons, but for ions the scale of magnetosphere is so small that it allows their acceleration only up to 100 keV. We present comparative analysis of the efficiency of various acceleration mechanisms (inductive acceleration, acceleration by the centrifugal impulse force, stochastic acceleration in a turbulent magnetic fields, wave–particle interactions and bow shock energization) in the magnetospheres of the Earth and Mercury. Finally we discuss several points which need to be addressed in a future Hermean missions.