Energization of particles in Saturn's inner magnetosphere: Monte Carlo simulation of stochastic electric field effects

Institute of Geophysics, Department of Space Physics, National University of Mexico, Ciudad Universitaria 04510, Mexico e-mail: affabeca@gmail.com; hdurand_manterola@yahoo.com; perezdet@geofisica.unam.mx

Received: 10 October 2006
Accepted: 23 April 2007

Abstract

Context.Our knowledge of energetic particles in Saturn's inner magnetosphere is based on observations made during the flybys of Pioneer 11, Voyager 1, Voyager 2, and recently by Cassini. The most important features of the energetic particle population in the inner Saturnian magnetosphere are: 1) the rings and the many large and small satellites inside this region reduce the population of particles whose energies are higher than 0.5 MeV to values of the order of 10³ times less than would otherwise be present; 2) the sputtering and outgassing of the surfaces of the satellites injects particles into the system and by some physical process, particles of the resultant plasma are accelerated to energies of the order of tens of keV; 3) the radial distribution of very energetic protons E_p > tens of MeV exhibits three major peaks associated with rings and satellites; 4) a proton population E_p ~ 1 MeV lies outside the orbit of Enceladus; 5) a proton population E_p < 0.25 MeV has an apparent origin associated with Dione, Tethys, Enceladus, E-ring, Mimas, and G-ring; 6) a population of low-energy electrons is associated with the satellites.

Aims.We propose a mechanism to explain the energetic particle population observed in Saturn's inner magnetosphere based on the stochastic behavior of the electric field.

Methods.To simulate the stochastic electric field we employ a Monte Carlo Method taking into account the magnetic field fluctuations obtained from the observations made by Voyager 1 spacecraft.

Results.Assuming different initial conditions, like the source of charged particles and the distribution function of their velocities, we find that particles injected with very low energies ranging from 0.104 eV to 0.526 keV can be accelerated to reach much higher energies ranging from 0.944 eV to 0.547 keV after a few seconds.