Titan [TY-tun] is the largest moon of Saturn and the second largest moon in the solar system, rivaled only by Jupiter's moon Ganymede. Before the Voyager encounters, astronomers suspected that Titan might have an atmosphere. Scientists also believed they might find liquid seas or pools of methane or ethane; water would be frozen due to Titan's low surface temperature. Expecting an unusual world, Voyager 1 was programmed to take numerous close up views of Titan as it flew past in November of 1980. Unfortunately, all that was revealed was an impenetrable layer of atmosphere and clouds. Only slight color and brightness variations were observed. .
Although Titan is classified as a moon, it is larger than the planets Mercury and Pluto. It has a planet-like atmosphere which is more dense than those of Mercury, Earth, Mars and Pluto. The atmospheric pressure near the surface is about 1.6 bars, 60 percent greater than Earth's. Titan's air is predominantly made up of nitrogen with other hydrocarbon elements which give Titan its orange hue. These hydrocarbon rich elements are the building blocks for amino acids necessary for the formation of life. Scientists believe that Titan's environment may be similar to that of the Earth's before life began putting oxygen into the atmosphere. .
Titan's surface temperature appears to be about -178°C (-289F). Methane appears to be below its saturation pressure near Titan's surface; rivers and lakes of methane probably don't exist, in spite of the tantalizing analogy to water on Earth. On the other hand, scientists believe lakes of ethane exist that contain dissolved methane. Titan's methane, through continuing photochemistry, is converted to ethane, acetylene, ethylene, and (when combined with nitrogen) hydrogen cyanide. The last is an especially important molecule; it is a building block of amino acids. .
The Voyager spacecrafts were not able to penetrate the thick layers of clouds but they did reveal that Titan is one of the more interesting places in the solar system.