Galileo In-Situ Dust Measurements and the Physics of Jupiter's Gossamer Rings

Details Galileo In-Situ Dust Measurements and the Physics of Jupiter's Gossamer Rings Galileo In-Situ Dust Measurements and the Physics of Jupiter's Gossamer Rings

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p43b1289k&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P43B-1289

Physics

6015 Dust, 6213 Dust, 6218 Jovian Satellites, 6220 Jupiter, 6265 Planetary Rings

Scientific paper

During its late orbital mission about Jupiter, the Galileo spacecraft flew twice through the giant planet's gossamer ring system. The dusty ring material is produced when interplanetary impactors collide with embedded moonlets. Optical images imply that the rings are constrained both horizontally and vertically by the orbits of the moons Amalthea and Thebe with the exception of a faint outward protrusion called the Thebe Extension. During the ring passages, the Galileo impact-ionization dust detector counted a few thousand impacts but only about 100 complete data sets of dust impacts (i.e. impact time, impact speed, mass, impact direction, etc.) were successfully transmitted to Earth. The instrument verified the outward extension of the gossamer ring beyond Thebe's orbit and measured a major reduction in particle ring material interior to Thebe's orbit. The existence of this partially evacuated gap in ring material is also indirectly confirmed by Galileo in-situ energetic particle measurements (Norbert Krupp, priv. comm.). Detected particle sizes range from about 0.2 to 4 micron, extending the size distribution by an order of magnitude towards smaller particles than previously derived from optical imaging (Showalter et al., Icarus 2007). The grain size distribution increases towards smaller grains, showing a much higher proportion of small particles in the Amalthea gossamer ring than in the Thebe ring and the Thebe Extension. Our analysis shows that particles contributing most to the optical cross-section are about 4 micron in radius, in agreement with imaging results. Finally, Galileo also detected some micron and sub-micron grains on highly inclined orbits with inclinations up to 20 degrees. Recent modelling (Hamilton & Krueger, Nature, submitted) shows that time variable electromagnetic effects 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. The model also puts strong dynamical constraints on the local plasma density.

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