Dione Flyby

Revolution 16 began with apoapsis at 41.2 planetary radii on 2 October 2005, and there was a non-targeted fly-by of Titan at a range of 776,267 kilometres on 10 October. The next day, Cassini flew by Dione at an altitude of 500 kilometres. Its surface was heavily cratered, but in the bright wispy terrain it was fractured as a result of tectonism. In fact, there were multiple generations of fractures. Numerous fine parallel grooves were interrupted by larger irregular bright fractures. In several places, fractures interrupted deposits on the floors of craters. As B.J. Buratti of the Visual and Infrared Mapping Spectrometer team ventured, ''Dione appears to be an older sibling of Enceladus. We think the cracks may be an older version of the 'tiger stripes' on Enceladus.'' The Ultraviolet Imaging Spectrograph detected water-ice.

The ice in the fractures was different to that on the adjacent terrain, possibly due to a variation in the grain size. Variations in albedo may have been due to downslope movement exposing 'clean' ice on steep flanks and darker material accumulating in topographic lows. The Voyagers had reported a concentration of magnetospheric ions near Dione's orbit, and the existence of the wispy terrain had given rise to speculation that this might indicate outgassing adding to the 'E' ring, but Cassini's magnetospheric and plasma science instruments found no sign of an envelope. Nevertheless, brief orbital resonances with Enceladus could have driven such activity in the past. As regards the magnetospheric ions near Dione's orbit, the Plasma Spectrometer found these to be neutrals that had been released by Enceladus and drifted outwards in the 'E' ring until, on reaching the most intense part of the magnetosphere, they had been ionised by electrons.267

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