Titan, the largest moon of Saturn, ranks as the second largest satellite in the solar system. Only Jupiter’s moon Ganymede is bigger. Titan’s diameter measures about 3,200 miles (5,150 kilometers)—larger than that of the planet Mercury. Measurements of Titan’s density suggest that its interior consists primarily of roughly equal amounts of rock and water ice.
Unlike any other moon in the solar system, Titan has a dense atmosphere. The air pressure on Titan’s surface measures about 1.5 times that on Earth’s surface. Titan’s atmosphere, like Earth’s, consists primarily of molecular nitrogen (N2). However, Titan’s atmosphere contains almost no oxygen. Because Titan lies far from the sun, its surface is extremely cold, around –290 °F (–179 °C). Liquid water and water vapor quickly freeze at these temperatures, but methane (CH4) forms a stable liquid and even produces clouds and rain in Titan’s atmosphere. High in the atmosphere, sunlight and charged particles from Saturn’s magnetosphere break apart methane to form other organic (carbon-based) compounds. These dark substances form a dense haze that obscures the moon’s surface.
Titan’s surface features a complex geography that appears to include dark dunes of organic sand, mountains covered by clouds of methane, volcanoes of water and ammonia ice, and systems of methane and ethane lakes and seas. Observations by scientists over several years have revealed that these lakes and seas change size. Methane rains and eruptions of water from inside the moon seem to have shaped Titan’s surface, much as Earth’s surface has been shaped by erosion and volcanic activity.
Loading the player...Volcano on Titan
The Dutch scientist Christiaan Huygens discovered Titan in 1655. In the late 1900’s, three United States space probes flew by Titan: Pioneer 11 in 1979, Voyager 1 in 1980, and Voyager 2 in 1981. None of these spacecraft could see through the haze to Titan’s surface. In 2004, the U.S. Cassini spacecraft began using radar data and special imaging techniques to study Titan’s surface. Despite the haze, images produced by Cassini have revealed evidence of cryovolcanism (eruptions of liquid water) on Titan. Cassini also released the European Space Agency’s Huygens probe. In 2005, Huygens parachuted through Titan’s atmosphere and photographed a region of bright icy hills cut by channels leading down to a dark plain. After landing, the probe detected methane and other organic molecules steaming out of Titan’s surface.
In 2012, Cassini scientists announced the discovery of a layer of liquid water deep beneath Titan’s surface. The layer is similar to the underground oceans believed to exist on several of Jupiter’s moons, including the three large moons Callisto, Europa, and Ganymede.
See also Cassini.
