The Stream Particle Observation During Cassini's Saturn Tour

Stream particles are nano-meter size dust grains accelerated by Saturn's corotational E field to high velocity (~ 100 km/s). By correlating stream particle impact rates registered by the Cassini dust detector with magnetic field data obtained by the Cassini magnetometer, we found that the stream particle impacts cluster during periods when the interplanetary field is characterised by interplanetary magnetic field (IMF) direction. Furthermore, the directionality and the impact charge of the streams are highly correlated with the corotating interaction region (CIR). The strong correlation between the stream partciles activity and IMF suggests that the dynamics of the stream particles is dominated by the electromagnetic force. Another consequence is that the typical size of a Saturnian stream particle is below 20 nm. Using dust and solar wind measurements from Cassini spacecraft, we perform backward simulations using a method employed first by Zook et al. (1996) to investigate the propagation of Jovian stream particles. The result shows that the most likely source region of Saturnian streams locates between 7 to 9 RS (Saturn radii). The velocity of the stream particles ranges from 40 to 200 km/s. Their charge-to-mass ratio ranges from 1000 to 10,000 C/kg, which is equivalent to 10 to 3 nm if assuming +5 volt surface potential.