Although the D ring of Saturn is so thin that it's barely noticeable compared to the rest of the ring system, it still displays structures seen in other Saturnian rings. Here the spiral structures in the D ring are on display.
The D ring spirals, discovered in Cassini images, are believed to be due to a warp in the ring created in the early 1980s. The precise mechanism remains the subject of scientific debate. Over the course of the Cassini mission, scientists have been able to observe the spiral winding ever more tightly as it evolves. For more about the spiral, see Tilting Saturn's Rings and A Twisted Tale.
(The bright specks and faint vertical streaks are merely image artifacts. The processes typically employed to remove these artifacts would also have degraded the exquisite details of the D ring which are visible here.)
This view looks toward the sunlit side of the rings from about 22 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 6, 2013.
The view was acquired at a distance of approximately 350,000 miles (563,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 131 degrees. Image scale is 2.1 miles (3.4 kilometers) per pixel.
Credit: NASA/JPL-Caltech/Space Science Institute