The Planetary Society Blog

What's the halo around Tethys? Has something - passing through Enceladus' fountains - deposited a film on the camera lens?

That's an artifact of the way the images are compressed before being posted to the raw images website. They're converted to JPEG format when they are posted. JPEG is a "lossy" format, in which the image isn't represented as the actual values of each pixel, but instead as a bunch of overlapping functions. JPEG does a very good job of compressing images where the variations from one pixel to the next are smooth, but when there are sharp boundaries between areas of high pixel value and low pixel value, like where a bright moon is seen against black space, there can be those ghosting or halo effects. This is actually intentional on the Cassini mission's part -- by posting these images with JPEG compression, fine detail and some data quality is lost. The images are still quite good enough for the public to play with, but it's not a good idea to use them for scientific interpretation. That helps the science team enjoy their proprietary data period until the data is formally archived and released to the Planetary Data System, which happens six to nine months after it is first acquired.

I think nutrino reflection phenomena occurs.
Or any other dark particle reflection phenomena occurs.

Its very rare. But in the icy planet , weak nutrino would destroy or reflection, I suppose.