A colour enhanced picture from Voyager 1 of layers extending to about 500 kilometres above Titan's surface. Titan, the 15th and largest of Saturn's moons, is unique amongst the moons of the Solar System in that it has an atmosphere. NASA's two Voyager spacecraft were launched in 1977 to explore the planets in the outer Solar System. An encounter with Titan was one of Voyager 1's main mision objectives, and it pased within 4000 kilometres of the moon. Much information was gained but, frustratingly, the thick, opaque atmosphere denied Voyager a view of the surface. The atmosphere is mainly nitrogen, with small amounts of argon, methane, other organic compounds such as ethane, hydrogen cyanide and carbon dioxide, and some water.
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