Saturn
Saturn was first explored by the Pioneer 11 spacecraft in September 1979. It flew as close as  above the planet's cloud tops. It took photographs of the planet and a few of its moons, but were low in resolution. It discovered a new, thin ring called the F ring. It also discovered that the dark ring gaps appear bright when viewed towards the Sun, which shows the gaps are not empty. The spacecraft measured the temperature of the moon Titan.