A cool picture from the Cassini spacecraft shows a piece of the rings of Saturn and four moons.  The giant in the background is Titan, Saturn's largest moon.  The next is Dione, the bright white moon in the foreground, complete with it's signature craters and ice cliffs.  Just outside the farthest ring is Pandora, only 80 kilometers across, and which shepherds the outside of the furthest narrow F ring.  Finally, barely visible, is Pan, inside the smaller gap in the rings, appearing here as a tiny bright speck.  It is barely 35 kilometers in diameter, and its job is to keep the smaller of the two ring gaps that we see here, known as the Encke gap, clear of debris.