Stream particles as the probe of the dust-plasma-magnetosphere interaction at Saturn

Abstract

[1] We analyze the dynamics and composition of Saturnian stream particles measured by the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft. To reconstruct the dynamical properties of Saturnian stream particles, we adopt a backward tracing method with in situ solar wind measurements to filter out the influence of the interplanetary magnetic field. Our results show that stream particles from Saturn have sizes ranging from 2 to 8 nm (radius) with ejection velocities between 50 and 200 kms−1. Moreover, the derived “ejection region” of stream particles in the outer part of Saturn's E ring is indicative of the dust charging condition profile in the planet's magnetosphere. By using the Cassini magnetospheric plasma measurements as input, our ejection model considers stochastic charging and well reproduces the dynamical properties of stream particles derived from backward simulations. An updated analysis of CDA stream-particle mass spectra confirms that the silicateous material is the most probable composition of Saturnian stream particles, in contrast to E ring particles whose composition is dominated by water ice. This compositional discrepancy can be reproduced by our model if the different sputter efficiencies of silicateous material and water ice are considered. We suggest that silicateous impurities released from icy grains at the outer E ring are the most probable source of Saturnian stream particles. Finally, we discuss the role of dust particles as a mobile neutral reservoir in Saturn's magnetosphere which may be responsible for certain features in the Cassini O and O2+ measurements.