Motions of Energetic Electrons and Ions in the Vicinity of Europa

Because of the increasng interest in a new mission to Europa in the form of Europa Orbiter, the issue of the radiation environment near this Jovian moon has attracted renewed attention. This is because a better description of the fluxes of energetic charged particles will be important to understanding of the radiolysis of the surface icy materials which holds the key to the chemical compositions in different regions of Europa's surface and the production of the oxygen atmosphere. In addition, such study should be of use to mission design concerning the radiation dosage to be endured by the spacecraft. It is also known that the motions of energetic electrons and ions are significantly influenced by the magnetic and electric fields near Europa which are modified by its interaction with the Jovian magnetosphere. For this reason, resistive MHD model simulations of Europa's plasma and field environment have been carried out taking into account the induced dipole field generated by the time-variation of the planetary magnetic field as a result of the flapping of the Jovian current sheet. The viability of this set of model calculations will be examined by comparison to the magnetic field measurements from the Galileo magnetometer observations during several of the Europa encounters. Results of some test runs of particle trajectory calculations for MeV electrons and ions will be reported.