Galileo in-situ dust measurements and the sculpting of Jupiter's gossamer rings by its shadow

Details Galileo in-situ dust measurements and the sculpting of Jupiter's gossamer rings by its shadow Galileo in-situ dust measurements and the sculpting of Jupiter's gossamer rings by its shadow

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..951k&link_type=abstract

European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a

Computer Science

Scientific paper

Galileo was the rst arti cial satellite to orbit Jupiter. During its late orbital mission the spacecraft made two passages through the giant planet's gossamer ring system. The highly sensitive impact-ionization dust detector on board successfully recorded dust impacts during both ring passages and provided the rst in-situ measurements from a dusty planetary ring. During the rst passage { on 5 November 2002 while Galileo was approaching Jupiter - dust measurements were collected until a spacecraft anomaly at 2:33RJ (Jupiter radii) just 16 min after a close yby of Amalthea put the spacecraft into a sa ng mode. The second ring passage on 21 September 2003 provided ring dust measurements down to about 2:5RJ and the Galileo spacecraft was destroyed shortly thereafter in a planned impact with Jupiter. In all, a few thousand dust impacts were counted with the instrument accumulators during both ring passages, but only a total of 110 complete data sets of dust impacts were transmitted to Earth (Kr uger et al, Icarus, submitted). Detected particle sizes range from about 0.2 to 5 m, extending the known size distribution by an order of magnitude towards smaller particles than previously derived from optical imaging (Showalter et al., Icarus 2008). The grain size distribution increases towards smaller particles and shows an excess of these tiny motes in the Amalthea gossamer ring compared to the Thebe ring. The size distribution for the Amalthea ring derived from our in-situ measurements for the small grains agrees very well with the one obtained from images for large grains. Our analysis shows that particles contributing most to the optical cross-section are approximately 5 m in radius, in agreement with imaging results. The measurements indicate a large drop in particle ux immediately interior to Thebe's orbit and some detected particles seem to be on highly-tilted orbits with inclinations up to 20 . Finally, the faint Thebe ring extension was detected out to at least 5RJ, indicating that grains attain higher eccentricities than previously thought. The drop interior to Thebe, the excess of submicron grains at Amalthea, and the faint ring extension indicate that grain dynamics is strongly in uenced by electromagnetic forces. Recent modelling (Hamilton & Kr uger, Nature, 2008) shows that time variable electromagnetic e ects (shadow resonance) can account for all of these surprising results. In particular, when the ring particles travel through Jupiter's shadow, dust grain electric charges vary systematically, driving grains out into the Thebe Extension and matching the Galileo in-situ dust measurements.

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