High-altitude clouds—about 40 kilometers (25 miles)—above the surface of Titan do not contain water vapor like here on the Earth. Instead, they are believed to contain methane, ethane, and other hydrocarbons (compounds consisting of the elements hydrogen and carbon). With these pictures, scientists are more confident that weather cycles exist on Titan in which these hydrocarbon clouds rain down methane and other organics onto the moon’s surface to form lakes and maybe even oceans. The liquids then evaporate to form more cloud systems. In addition, scientists believe that the overall lower atmosphere of Titan consists mostly of nitrogen, with smaller amounts of hydrocarbons.

Cassini will be flying past Titan on over 40 different occasions in the future, so scientists will be able to monitor the activity of the cloud system at various stages. It is believed that such cloud formations last for about 25 Earth-years before disappearing for about five Earth-years, only to reappear again for another cycle.

The Cassini mission is an international project between NASA, the European Space Agency (ESA), the Italian Space Agency, and other academic and commercial organizations. It was named for French-Italian astronomer Jean-Dominique Cassini, who discovered a gap in Saturn's main rings—what is now called the Cassini Division.

The Cassini spacecraft began its mission on October 15, 1997. It traveled about 2.175 billion miles (3.5 billion kilometers) in order to reach Saturn and its system of rings and moons on June 30, 2004. After Cassini went into orbit about Saturn, it began sending back images and data to the Earth. It will continue to explore the Saturnian system for at least four years. Cassini uses a number of specialized cameras and other instruments for its investigation of Saturn, Titan, and other members of the system. For instance, the Magnetosphere Imaging Instrument (MIMI), designed by scientists from Johns Hopkins University’s Applied Physics Laboratory, will observe the highest layer of Titan’s atmosphere (the exosphere).

Titan is the second-largest moon in the solar system, being about twice the diameter as the Earth’s Moon. It is one of only two known moons within the solar system to have a fully-developed atmosphere. Titan's atmosphere is so cloudy that detailed observations of the inner atmosphere and surface have been limited. However, on December 25, 2004, Cassini released its Huygens probe, which descended into the Titan atmosphere on January 14, 2005. It reached the surface of Titan, where it relayed information back to the Earth about the atmosphere and surface.

Scientists believe that lakes and oceans of liquid hydrocarbons formed by methane rain falling on the surface may occur. If proven correct, such weather activity may be similar to what occurred in the early history of the Earth. Thus, an understanding of Titan’s atmosphere and cloud formations could possibly help scientists understand the origin of life on the Earth.

More information about the Cassini-Huygens mission can be obtained at: (NASA) http://www.nasa.gov/mission_pages/cassini/main/ and (NASA Jet Propulsion Laboratory) http://saturn.jpl.nasa.gov/home/index.cfm.

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