As I was watching the grand finale of Cassini and listening to the mission team talk about the accomplishments of the mission, I learned a little bit about propellors.  Not your typical airplane propellor, but the name used to describe this fascinating feature in Saturn’s rings. Seeing Saturn’s rings from afar, or even relatively close with Cassini, we see the rings as perfect.  How do we end up with strange features and imperfections like this one?  Looking elsewhere in the rings, we can find clues. The first clue is the namesake of the mission itself.  The Cassini spacecraft was named for...