Titan's atmosphere
NASA's Voyager 1 provided the first detailed images of Titan in 1980. They showed only an opaque, orange atmosphere, apparently homogeneous.
It was so thick that you could not see the surface. However, other data revealed exciting things. Similarly to Earth, Titan's atmosphere is mostly nitrogen but there is also methane and many other organic compounds.
Images from the ground-based WM Keck Observatory revealed methane-containing clouds near Titan's south pole, hinting that Titan could have the equivalent of a weather cycle similar to ours on Earth.
The Cassini orbiter could clearly see these clouds, and monitor changes throughout the entire mission.
