Saturn's Rings
Pioneer grabbed this great image of Saturn's famous rings and one of its moons, possibly Rhea. During its flyby, the probe crossed the plane of the great rings twice, once inbound and once again outbound.
A few minutes after the first ring plane crossing, Pioneer 11 nearly slammed right into a moon. Rates of energetic particle detections dropped dramatically and magnetic readings changed quickly, indicating that the spacecraft had passed right through the magnetic wake of a moon. Two moons are now known to orbit in that area, Epimethius and Janus, and to this day no one knows which one Pioneer nearly hit.
Images: 1) NASA 2) A close-up view of Titan that Pioneer made during its flyby NASA