Figure 6. Number density of micrometer-sized dust particles between 6 and 30 Rj constructed from the Galileo measurements. The orbits of the Galilean satellites are indicated by vertical dashed lines. Only data from Galileo orbits 124 to 133 are shown because earlier orbits only partially traversed the region between Io and Europa. Dust cloud particles identified in the close vicinity of the moons are not shown.
techniques. Only a highly sensitive detector of the Galileo/Ulysses type could recognize a sufficient number of grains to detect these clouds. The low dust density is illustrated by the fact that only 35 cloud particles impacted the detector during 4 fly-bys at Ganymede
A detailed analysis of the entire Galileo dataset for the three Galilean satellites is ongoing. One goal is to check for signatures of a leading-trailing asymmetry of the ejecta clouds, which can be expected from the orbital motion of the satellite with respect to the field of impactors .
The Galileo measurements are the first successful in-situ detection of satellite ejecta in the vicinity of a source moon. All celestial bodies without gaseous atmospheres (asteroids, planetary satellites of all sizes) should be surrounded by an ejecta dust cloud. Before Galileo, there were few attempts of direct in-situ detections of ejecta close to satellites — most notably, near the Moon , These experiments, however, did not lead to definite results.
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