Formation of the Thebe Extension in the Ring System of Jupiter

摘要

Jupiter's tenuous dust ring system is embedded in the planet's inner magnetosphere, and-among other structures-contains a very tenuous protrusion called the Thebe extension. In an attempt to explain the existence of this swath of particles beyond Thebe's orbit, Hamilton and Kruger (2008), proposed that the dust particle motion is driven by a shadow resonance caused by variable dust charging on the day and night side of Jupiter. However, the model by Divine and Garrett (1983), together with recent observations by the Juno spacecraft indicates a warm and rather dense inner magnetosphere of Jupiter which implies that the mechanism of the shadow resonance does not work. Instead, we argue that dust grains ejected from Thebe due to micrometeoroid bombardment become the source of dust in the Thebe extension. We show that large (grain radii of a few micrometers up to multi-micrometers) charged dust grains having significant initial velocities oscillate in the Thebe extension. Smaller charged grains (with sub-micrometer radii) ejected from Thebe do not spend much time in the Thebe extension and migrate into the Thebe ring. At the same time, if such grains are ejected from larger dust grains in the Thebe extension due to fragmentation, they continue to oscillate within the Thebe extension for years. We argue that fragmentation of large dust grains in the Thebe extensions could be the main source of sub-micrometer grains detected in the Thebe extension.