Titan landscape. Computer artwork of the surface of Titan, the largest moon of the ringed planet Saturn (left). Titan is known to have traces of complex hydrocarbon compounds in its nitrogen atmosphere. These form as sunlight acts on the methane in Titan's upper atmosphere. Clouds of methane and ethane vapour could produce rain to form rivers and oceans of hydrocarbons on the surface. Titan orbits over 1.2 million kilometres from Saturn, a ringed gas giant planet that is the sixth planet from the Sun. The gravity on Titan is about a seventh of Earth's. Surface temperatures are as cold as -183 degrees Celsius.