Energetic Proton and Electron Distributions in Saturn Magnetosphere as Revealed by Cassini / Voyager Observations and Proposed by Models

Before the arrival of Cassini at Saturn in July 2004, our knowledge of energetic protons and electrons (energy > 10 KeV) in Saturn's magnetosphere, radial distances r < 12 Rs was mainly based on the particle observations made during the flybys of Pioneer 11 (September 1979), Voyager 1 (November 1980), and Voyager 2 (August 1981). Models of radiation belts have then been developed from direct processes of particles data (LECP) (empirical model) or from physical models drawn on the adiabatic invariant theory and the resolution of the governing Fokker-Planck transport equation. These models have been used to increase our understanding of Saturn radiation belt dynamics, and to predict Cassini observations of particle fluxes (MIMI/LEMMS instrument) and energetic neutral atom emissions (MIMI/INCA instrument). The measurements obtained during the insertion of Cassini at Saturn displayed important differences between predictions and observations. Furthermore, an unexpected new radiation belt in the innermost part of the magnetosphere has been discovered. These new observations have demonstrated that Cassini will provide important new knowledge of Saturn's magnetosphere and revisions of models will need to be considered. We present a preliminary update to our model based on recent LEMMS data. We will discuss both the differences between LEMMS observations and predictions, and the changes made in our model (plasma injection, physical processes, magnetic field model, etc.) in order to reproduce the recent Cassini observations.