Geometric Structure of the E Ring
Vertical Ring Profile:
Within the dense parts of the E ring, the DA is not able to measure the impact rate because the number of impacts detectable by the DA is limited to 60 per minute and the E ring particles hit the detector more frequently so that the detector is saturated. This is the moment of truth for the High Rate Detector (HRD). During the first 2 years of the Cassini tour we obtained excellent HRD data when the spacecraft steeply crossed the Saturnian ring plane. Such crossings are particularly useful for determining the ring‘s vertical structure at the distance of the ring plane piercing. Here we show a few examples of such crossings:
Vertical ring profile at about the Enceladus orbit (3,95RS, Saturnian radius RS = 60330 km). Shown are the impact rates and the corresponding number densities of grains >0.9µm and >1.6µm. The vertical ring thickness (FWHM) is about 4200 km. The densest point lies outside the Enceladus orbit at about the Mimas orbit (3.08RS). Here the vertical ring thickness (FWHM) is about 5400 km. The southward symmetry offset of 1200km with respect to the geometric equator is remarkable.
Radial Ring Profile:
The global radial distribution of E ring particles is studied best during long equatorial scans of the ring. This condition was partially met during Cassini‘s third orbit around Saturn. Based on this data together with results of the various orthogonal crossings of the ring plane we established a simple geometric model of the E ring structure that reproduces the data well.
Spatial distribution of E ring particles inferred from rate measurements inside 6RS during the inbound leg of orbit 3. Grey areas mark data gaps. The white lines show the predictions by the geometric model.
Spatial particle distribution derived from the outbound orbit 3 measurements. The discrepancy between data and model predictions is due to the enhanced dust density in the vicinity of the ring moon Enceladus.
- S. Kempf et al., How the Enceladus dust plumes feeds Saturn’s E ring, Icarus, 2010, 206, 446457
- M. Horanyi et al. Diffuse Rings in Saturn from Cassini-Huygens, Springer, 2009, 509–534
- S. Kempf et al., The E ring in the vicinity of Enceladus I: Structure and properties of the Enceladus, Icarus, 2008, 193, 420-437.
- R. Srama, R. et al., Dust measurements at Saturn, Plan. Space Sci., 2006, 54, 967-987