The velocity distribution functions of oxygen and sulphur ions in the Io plasma torus

The Smith-Strobel model for the energy transfer and ion velocity distributions of the Io torus plasma is updated to take into account the heating effect of the secondary hot electrons and hot ions. The new radiative cooling rates - which led to the current energy crisis in the maintenance of the ultraviolet emission of the Io plasma torus - are also used in the computation. It is found that reasonable agreement with the Voyager observations can be achieved with such external contributions. It is expected that comparison of the theoretical models with the Galileo observations would provide very useful guidance in our understanding of the complicated processes involved in the energy coupling among the different ion and electron populations in the inner Jovian magnetosphere.