Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p34a..08w&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #P34A-08
Other
5759 Rings And Dust
Scientific paper
The plasma wave instruments on Voyager 2 and Cassini have detected impacts of micron-sized particles during passes through Saturn's ring plane, at 2.88 RS and 2.63 RS, respectively. Previous researches based on dust impacts recorded by plasma wave instruments on these two spacecrafts have given a set of parameters of the dust particles in these two regions. For the region where Voyager 2 passed through, the number density is 15 × 10-3 m-3, the dust particle sizes are of the order of 10 μm, and the corresponding particle masses are of the order of 10-9g. For the region where Cassini crossed, the number density is 6 × 10-3 m-3, the root-mean -square size is about 2μm, and the corresponding root-mean--square mass is 7.7×10-11g. The dust distributions in these two regions consist of a core component and a less dense halo component. At 2.88 RS, the Voyager 2 dust impact data showed that the thickness of the primary distribution is 2ΔZ = 962 km and the thickness of the halo part is 2ΔZ =3376 km. At 2.63 RS, the Cassini dust impact data showed that the thickness of the core part is 2ΔZ = 300 km and the thickness of halo part is about 2ΔZ = 700 km. In this paper, we present calculations of optical depth based on the dust parameters and compare our results with the Cassini imaging team's observations of scattered light from the same regions. The optical depth computed from the dust impact observations at 2.63 RS is 10-7. This result is lower than the optical depth obtained from the Cassini optical imaging, which is about 10-6. One possible reason is that the Cassini plasma wave instrument can not detect small particles below the 1.6 mV detection threshold and these small particles contribute a lot to the optical depth. Much better agreement between our calculations and image team's observations are realized if we make a plausible assumption for under the same power law, the size distribution of dust particles extends below the RPWS detection limit by about a factor of 10. Another possible reason is that the effective area used to compute the number density is too large for the Cassini dust impact measurements. This brings a lower number density and subsequently, a lower optical depth. Right now, we are not sure about the exact effective area. The comparison with imaging observations may help to calibrate the effective impacting area.
Burns Joseph A.
Gurnett Donald A.
Hedman Matthew M.
Kurth Willaim S.
Spangler Steven R.
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