While the film 2001: A Space Odyssey sees a fantastic mission to the planet Jupiter, the novel sees the spaceship Discovery instead headed for this moon of Saturn. In the novel, David Bowman finds a large black monolith standing out against this moon's white surface. In reality, this moon is best known for being "two-toned", that is one side being very light, and the other side being incredibly dark. While the dark hemisphere of this moon is named for its discoverer, Giovanni Cassini, almost all of its other features have names taken from The Song of Roland. Name this third largest moon of Saturn.