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K. -U. Thiessenhusen, F. Spahn (Universit\"at Potsdam), H. Kr\"uger, E. Gr\"un (Max-Planck-Institut f\"ur Kernphysik)
During several passages in the inner Jovian system, the dust detector system (DDS) onboard Galileo recorded a number of dust events caused by large, about micron sized dust particles. Such grains can be expected to have nearly Keplerian orbits around Jupiter.
The knowledge of the origin of those long-lived particles is of special interest for the understanding of the dynamics of planetary ring systems. Colwell et al. (Science, 280, 88-91) suggested that these particles are interstellar or interplanetary grains captured in the Jovian magnetosphere. Such a capturing mechanism would provide retrograde orbits for about 80 dust data showed that indeed almost all of the strongest recorded dust impact events are caused by particles one retrograde orbits. But this effect deceives about the true nature of this dust ring. The Galileo data indicate that the number of prograde particles is much higher than that of retrograde ones.
The detection of the impacts is strongly influenced by the motion of Galileo itself. Prograde particles cause much weaker impacts than retrograde ones. Therefore, the total density of this faint ring might be much higher than expected.