One of the principal objectives of the Voyager 1 mission was the study of Titan. Voyager 1 came within 4000 km of the surface. We learned more in the few minutes of that encounter than in the previous 300 years. And yet our knowledge is frustratingly incomplete. All that the Voyager images show is a slight variation in color between the northern and southern hemispheres.
Titan is about half water ice and half rocky material.
It is probably differentiated into several layers with a 3400 km rocky center surrounded by several layers composed of different crystal forms of ice. Its interior may still be hot. Though similar in composition to Rhea and the rest of Saturn 's moons, it is denser because it is so large that its gravity compresses its interior. Alone of all the satellites in the solar system, Titan has a significant atmosphere . The organics are formed as methane, which dominates in Titan's upper atmosphere, is destroyed by sunlight.