Orbit Plane Shadows

Credit: NASA/JPL/Space Science Institute
Image source with more info

Cassini has sent quite a few images like this over the past month, probably because they depict something that you only really get to see if you're orbiting Saturn around about the time of its equinox: several of its moons are now casting their shadows onto the rings.

This particular shadow is being thrown by Death Star look-alike Mimas, which isn't itself pictured.