Saturn‘s E ring

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Saturn's diffuse E ring is the largest planetary ring in the solar system, encompassing the ice moons Mimas (distance to Saturn 3.07RS), Tethys (4.88RS), Dione (6.25RS), and Rhea (8.73RS). The moon Enceladus has been proposed early as the dominant source of ring particles because the edge-on brightness profile peaks near the moon‘s mean orbital distance. Perhaps the most striking finding is the unusual blue colour of the ring implying a narrow grain size range centred between 0.3µm and 3µm. The CDA data, however, are somewhat in conflict with this conclusion.

The ring is composed of ice particles. The peak number density is of the order of 1 particle within 1m3. The low number density implies that the particle dynamics is not collisional but due to the various perturbing forces acting on the grains.
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Geometric ring structure:


There is an intimate connection between the vertical ring structure and the properties of the grains ejected by the source moon Enceladus.
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Enceladus as the main ring particle source:


From the Enceladus south pole terrain emerge collimated ice particle jets. The grains condense from water vapour expanding inside the fractures in the moon‘s surface, while the size and speed distribution of the jet particles is established by wall collisions during their ascent.

Ring particle composition:


The E ring particles mostly consist of pure water ice. The CDA mass spectra of E ring particles also show traces of non-water materials, which may provide information about the main ring particle source - the ice moon Enceladus.