アイテム詳細

要旨

The Cassini spacecraft encountered Jupiter for a swingby manoeuvre in late 2000. The Cosmic Dust Analyser onboard was able to record mass spectra of impact events from dust stream particles . These particles are driven out from the Jovian magnetosphere and were detected at a distance of about 1 AU from the gas giant. To extract the chemical composition of particles, comprehensive statistical analysis of the dataset was accomplished. The results strongly imply that the vast majority of the stream particles are originated from the Jovian satellite Io. Sodium chloride (NaCl), sulfurous components and potassium were identified as particle constituents. Quantitative estimations suggest that NaCl is the most abundant component which is in contrast to observations of the Ionian atmosphere, the plasma torus and the neutral cloud, where sulfur species are dominant while alkali and chlorine species are minor components. This finding indicates that alkaline salt condensation of volcanic gases is the dominant formation process for particles reaching the Ionian exosphere.