Io as the trigger of energetic electron disturbances in the inner Jovian magnetosphere

Abstract

Io adds approximately a ton of mass per second to the Jovian magnetosphere, mass that is consequently energized to circle Jupiter at the corotation velocity with a commensurate thermal velocity. The plasma moves radially outward and eventually is lost down the tail. The mass addition process and its subsequent transport are far from uniform and are thought to be ultimately responsible for driving much of the dynamics of the Jovian magnetosphere. One of the manifestations of this dynamic behavior is a disturbance of the energetic electron fluxes measured by the Galileo spacecraft. When we examine disturbances in the dipolar portion of the magnetosphere, that we conservatively take to be within 12 Jovian radii ( R J ), we find that energetic electron events are more often seen on passes in which Io is close to Galileo's perijove longitude. The majority of these events occur when Galileo is within ±25° of Io. For those events for which injection longitudes can be calculated, the injection point is consistent with the longitude of Io at the time of injection. This correlation suggests that disturbances initiated by Io are affecting energetic particles as far out as jovicentric distances of 12 R J , 6 R J outside the Io orbit.