Titan is the largest of Saturn’s 30 or more known moons. Easily visible through a telescope as a bright‘star like’ object near Saturn’s rings, Titan is larger than our own moon and larger than Mercury and Pluto.
Titan has held much intrigue for scientists because of its thick atmosphere, the only moon in the solar system with such a feature. Recent studies have confirmed the presence of complex organic chemistry which reinforces the idea that Titan is a promising place to observe the molecules that may have been the building blocks of life here on Earth.
In January 2005, the Huygens probe dropped into the upper layer of the atmosphere and landed on the surface of Titan. Clear images of the surface were obtained revealing an extraordinary world resembling Earth in many respects such as meteorology and geography. The images show strong evidence for erosion by liquid flows caused by methane.
Titan's Atmosphere
The Saturn Ring System
There are scattered variable clouds in Titan's atmosphere in addition to an overall thick haze. These clouds are probably composed of methane, ethane and other simple organics. Other more complex chemicals in small quantities are responsible for the orange color as seen from space.
Lower down in the atmosphere the thick haze is composed of complex organic molecules. The organics are formed from methane reacting with sunlight in Titan's upper atmosphere. The result is similar to the smog found over large cities, but much thicker. Titan’s atmosphere is similar in many ways to the conditions on Earth, early in its history, when life was first getting started. In addition to the thick hazy atmosphere making it hard to see Titan's features, it absorbs all but 10 percent of the sunlight reaching the surface. This and a weak greenhouse effect prevents the temperature on Titan from reaching any higher then minus 290˚ Fahrenheit.
Rivers of Methane
Bearing an uncanny resemblance to San Francisco bay, images from the Huygens probe show much of Titan’s surface to resemble features here on Earth, however, the hills are made of ice and the rivers have been carved by liquid methane! Liquid methane appears to have flowed from the high ice ridges, through ravines creating a river system which funnels into a delta with a long intricate shoreline. There are also short, stubby channels indicative of springs flowing out of the hillsides. While there are many signs of liquid on Titan, there is none currently visible. Titan may be typical of arid regions of Earth like Arizona, where riverbeds are dry most of the time. A wet season once a year may bring the methane rain which washes down the ice ridges and into rivers, then out into a broad plain where the “rain”settles into the ground and dries up. The area immediately surrounding the Huygens landing site appears to be a soft mud like mixture of ice, sand, methane and complex organic molecules.