The Characteristics of Dust Particles Detected by Cassini Near Saturn's Ring Plane

The Characteristics of Dust Particles Detected by Cassini Near Saturn's Ring Plane

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This thesis analyzes the dust impacts detected by the Radio and Plasma Wave Science (RPWS) instrument on the Cassini spacecraft during the inbound and outbound passes through Saturn's ring plane at 2.634 and 2.630 Saturn radii on July 1, 2004. When a small particle strikes the spacecraft at a high velocity, it is instantly vaporized and produces a small cloud of plasma that expands radially outward from the impact site. As the plasma cloud expands it produces a voltage pulse on the RPWS electric field antennas, the amplitude of which is proportional to the mass of the impacting particle. The impact rate at both ring plane crossings provides a good fit to the sum of two Gaussians, with a peak impact rate of about 1200 to 1500 impacts per second (the exact value depends on the voltage threshold used), and a north-south thickness of about 300 km. From the impact rate, effective cross-sectional area, and the relative velocity of the spacecraft, the number density of the impacting particles can be calculated and is estimated to be about 6 x 10-3 m-3. The mass distribution depends on the distance from the ring plane, and varies from about m a near the ring plane, at z = 0 +/- 100 km, where z is the north-south distance from the ring plane, to as steep as m-4 well away from the ring plane, at z = 500 +/- 100 km. The mechanisms involved in the impact detection are discussed and a formula relating the root-mean-square particle mass to the root-mean-square voltage on the antenna is derived. Using this formula, the root-mean-square mass is estimated to be 7.7 x 10 -11 grams, which for water ice particles with a density of 0.92 g cm-3 gives a root-mean-square radius of about 2.6 mum. To facilitate possible comparisons with optical observations, we have computed the expected optical depth and angular distribution of scattered light using the measured dust parameters. The optical depth normal to the ring plane at 500 nm is estimated to be about 4.26 x 10-8, and the full width at half maximum (FWHM) of the forward scattered light is estimated to be 9Ad.Encounter with Saturn: Voyager 1 imaging science results. Science, 212, 163- 191. Srama, R.; Ahrens, T. J.; Altobelli, N.; Auer, S.; Bradley, J. G.; Burton, M.; Dikarev, V. V.; Economou, T.; Fechtig, H.; Gorlich, M.; Grande, M.; Graps, A.; Griin, E.;anbsp;...

Title:The Characteristics of Dust Particles Detected by Cassini Near Saturn's Ring Plane
Author:Zhenzhen Wang
Publisher:ProQuest - 2006


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