  An interesting feature of the giant planets of our solar system is the
existence of regions around these objects where no irregular satellites are
observed. Surveys have shown that, around Jupiter, such a region extends from
the outermost regular satellite Callisto, to the vicinity of Themisto, the
innermost irregular satellite. To understand the reason for the existence of
such a satellite-void region, we have studied the dynamical evolution of Jovian
irregulars by numerically integrating the orbits of several hundred test
particles, distributed in a region between 30 and 80 Jupiter-radii, for
different values of their semimajor axes, orbital eccentricities, and
inclinations. As expected, our simulations indicate that objects in or close to
the influence zones of the Galilean satellites become unstable because of
interactions with Ganymede and Callisto. However, these perturbations cannot
account for the lack of irregular satellites in the entire region between
Callisto and Themisto. It is suggested that at distances between 60 and 80
Jupiter-radii, Ganymede and Callisto may have long-term perturbative effects,
which may require the integrations to be extended to times much longer than 10
Myr. The interactions of irregular satellites with protosatellites of Jupiter
at the time of the formation of Jovian regulars may also be a destabilizing
mechanism in this region. We present the results of our numerical simulations
and discuss their applicability to similar satellite void-regions around other
giant planets.
