~ 5

> 50 Rj

~ 10-8

*: derived from dynamical modelling, f: altitude above satellite surface.

Jovian dust populations studied in-situ with Galileo are summarised in Table 1.

All Galilean satellites are sources of dust in the Jovian system. The Galileo measurements have for the first time demonstrated the electromagnetic interaction of charged dust grains with a planetary magnetosphere. Jupiter's magnetosphere acts as a giant mass-velocity spectrometer for charged dust grains in space. The Io dust streams can be used as a potential monitor of the activity of Io's plume activity.

The Io dust stream particles probe the conditions in the Io plasma torus. Since in a completely radially symmetric plasma and magnetic field configuration no 10 h period should show up in the impact rate, only the 5 h period should be there. The prominent modulation of the rate with the 10 h period points to variations in the acceleration mechanism of the grains correlated with Jovian local time which are presently not completely understood.

In February 2004, Ulysses will approach Jupiter to 0.8 AU again. Additional dust stream measurements with Ulysses in interplanetary space at high jovigraphic latitudes and for varying Jovian local times will be beneficial to test our understanding of this new phenomenon.

The Galileo measurements of impact-generated dust clouds surrounding the Galilean satellites can be considered as unique natural impact experiments to study the dust ejection mechanism due to hypervelocity impacts onto celestial bodies without atmospheres. They complement laboratory experiments in an astrophysically relevant environment. Although far from being perfect impact experiments, the Galileo results offer two extremely important improvements over laboratory experiments: 1) the projectile and target materials and projectile speeds are astrophysically relevant, and 2) the masses and speeds of the ejecta particles can be determined in an important region of parameter space (micrometre sizes and kms-1 impact speeds). This is especially important in view of the Cassini mission. Cassini will start its exploration of the Saturnian system in 2004 and

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