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Abstract

In this work the time-of-flight mass spectra of cations, extracted from the plasma created by highvelocity particle impacts onto the Cassini dust detector, are evaluated. The composition of six different dust species is inferred. During Cassinis cruise, spectra of iron-rich interplanetary dust were obtained. Subsequently two fast hypervelocity stream particle species, originating from the Jovian and Saturnian systems were detected. For the Jovian streams sodium chloride (NaCl) was identified as the major particle constituent, accompanied by sulfurous as well as potassium-bearing components. This implies that the vast majority of the observed Jovian stream particles originate from the volcanically active Jovian satellite Io. An alkali salt condensation of gases inside Pele-type volcanic plumes is proposed as the source mechanism. For the Saturnian stream species the source region is the planets ring system. Silicon is identified as the main particle component, indicating that the tiny particles are probably remnants of once larger icy particles populating the outermost tenuous Saturnian ring, the E ring. Following Cassinis Saturn orbit insertion, three further spectral types have been discovered (during crossings of the E ring), associated with different particle populations. The bulk material of Type I and Type II particles is water ice. In contrast Type III dust exhibits a mineral composition. Type I spectra imply pure water ice particles, whereas in Type II spectra organic compounds and/or silicate minerals are identified as impurities within the icy particles. This reveals the cryo-volcanic plumes of the moon Enceladus as the origin of Type II particles, which implies a dynamic interaction of Enceladus rocky core with liquid water. The non-water Type III dust species exhibits an iron-rich composition, probably in the form of pyrite, oxides and/or hydroxides. A magnesiumrich siliceous subspecies is likely. Retrograde or unbound orbits are in best agreement with the Type III observations.