Cassini dust stream particle measurements during the first three orbits at Saturn

Stream particles are nanometer-scale dust particles ejected with speeds >= 100 km s(-1) from both the Jovian and Saturnian systems. Here we report the dynamical analysis of Saturnian stream particles on the basis of observations made by the Cosmic Dust Analyzer on board the Cassini spacecraft during its first three orbits around Saturn. The time span of the presented measurements covers from the beginning of orbit A to the end of orbit C (from the Saturn orbit insertion on 1 July 2004 UTC to 16 January 2005 UTC). During these orbits the Cassini spacecraft was usually located outside but not far from Saturn's magnetosphere. The Cassini observations therefore provide important information on the dynamics of stream particles just ejected from the system. As with earlier observations, two impact populations are identified. These appear as faint but continuous impacts as well as semiregular and energetic impact bursts. Faint impacts from directions close to the Saturn line of sight are recognized as recently ejected stream particles, while energetic dust bursts most probably consist of previously ejected particles that experienced significant acceleration within the solar wind. The presented measurements not only confirm the previous proposed stream particle ejection scenario but also serve as essential inputs for detailed dynamical modeling.