Energization of charged particles in planetary magnetospheres

Abstract

A model is presented to describe the energiza- tion of charged particles in planetary magnetospheres. The model is based on the stochastic acceleration produced by a random electric field that is induced by the magnetic field fluctuations measured within the magnetospheres. The sto- chastic behavior of the electric field is simulated through a Monte Carlo method. We solve the equation of motion for a single charged particle—which comprises the stochastic acceleration due to the stochastic electric field, the Lorentz acceleration (containing the local magnetic field and the corotational electric field) and the gravitational planetary ac- celeration of the particle—under several initial conditions. The initial conditions include the ion species and the ve- locity distribution of the particles which depends on the sources they come from (solar wind, ionospheres, rings and satellites). We applied this model to Saturn's inner magne- tosphere using a sample of particles (H + ,H 2O + ,N + ,O + and OH + ) initially located on Saturn's north pole, above the C-Ring, on the south pole of Enceladus, in the north pole of Dione and above the E-Ring. The results show that the particles tend to increase the value of their energy with time reaching several eV in a few seconds and the large en- ergization is observed far from the planet. We can distin- guish three main energization regions within Saturn's inner magnetosphere: minimum (Saturn's ionosphere), intermedi- ate (Dione) and high-energy (Enceladus and the E-ring). The resulting energy spectrum follows a power-law distribution