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The Cassini spacecraft encountered Jupiter in
late 2000. Still more than 1 AU away from the gas giant the Cosmic
Dust Analyser onboard the spacecraft recorded mass spectra of Jovian
stream particles for the first time. To determine the chemical
composition of particles, a comprehensive statistical analysis of
the dataset was performed. Our results imply that the vast majority
(>95%) of the observed stream particles originate from
the volcanic active Jovian satellite Io from where they are
sprinkled out far into the solar system. Sodium chloride (NaCl) was
identified as the major particle constituent, accompanied by
sulfurous as well as potassium bearing components. This is in
contrast to observations of gas in the Ionian atmosphere, its
corotating plasma torus, and the neutral cloud, where sulfur species
are dominant while alkali and chlorine species are only minor
components. Io has the largest active volcanoes of the solar system
with plumes reaching heights of more than 400km above the moons
surface. Our findings indicate that alkaline salt condensation of
volcanic gases inside those plumes could be the dominant
formation process for particles reaching the Ionian exosphere.
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