Four versions of the "F-Ring"

Caption NASA originale:"This montage of 4 images of Saturn's knotted F-Ring shows different locations around the Ring itself. Even though all the images were taken within a few hours of each other, there is remarkable variation in the structure of the F-Ring at these four locations.
For example, the number of ring strands differs from image to image and in some images, kinks are clearly visible in the F-Ring, while other regions appear more smooth.
Astronomers believe that the structure of Saturn's F-Ring is governed by its shepherding moons, Prometheus and Pandora. The F-Ring's appearance is expected to vary depending on how recently a ring section has encountered each moon and how close the moon came to the ring".

Nota: nel primo quadro (in alto a Sx) c'è qualcosa, posto proprio al di sopra del 'nodo' centrale visibile sull'intreccio più luminoso dell'Anello F, che sembra un 'filamento' o, comunque, un oggetto estraneo all'Anello F stesso, ma reale (NON crediamo che sia un photo-artifact). Cos'è?