Cassini Makes New Find in Titan’s Atmosphere

The blue patches in this image of Titan are thought to be hydrocarbon seas, formed from methane and other organic compounds in the moon’s atmosphere.

Washington — A U.S.-European space mission continues to offer Earth-bound scientists tantalizing discoveries about the Saturn moon Titan, the only moon in the solar system with an atmosphere.

NASA, the European Space Agency (ESA) and the Italian Space Agency launched the Cassini-Huygens mission to explore Saturn, its rings and its lunar system in 1997. The craft reached Saturn in 2004 and was the first to ever enter its orbit. In 2005 the Huygens probe left the orbiting Cassini craft, descended through Titan’s thick atmosphere and returned the first images of the moon’s surface.

Cassini’s latest discovery gives scientists greater understanding of the chemical ingredients in Titan’s atmospheric soup. Cassini’s Composite Infrared Spectrometer (CIRS) has identified the chemical propylene in Titan’s lower atmosphere. A September 30 NASA-ESA news release announced the discovery as the first definitive detection of this substance, used in making plastic, anywhere in the solar system besides Earth.

“This chemical is all around us in everyday life, strung together in long chains to form a plastic called polypropylene,” said Conor Nixon, a scientist at NASA’s Goddard Space Flight Center. Propylene is used in the manufacture of food-storage containers, car bumpers and other consumer products.

The finding expands on the understanding of Titan’s atmosphere, a body of knowledge in the making since 1980. NASA’s Voyager 1 spacecraft made the first-ever close fly-by of the Saturn moon in that era. The craft identified many of the gases in Titan’s atmosphere as hydrocarbons, the dominant components of petroleum and other fossil fuels used on Earth.

Through the years, various chemicals in the hydrocarbon family were identified in Titan’s atmosphere, but scientists were puzzled by the apparent absence of propylene. A more thorough analysis of the data collected by the CIRS instrument, which measures the heat radiation from Titan’s surface, detected the chemical.

“This measurement was very difficult to make because propylene’s weak signature is crowded by related chemicals with much stronger signals,” said Michael Flasar, Goddard’s principal investigator for CIRS. “This success boosts our confidence that we will find still more chemicals long hidden in Titan’s atmosphere.”

U.S. and European scientists are 1.2 billion kilometers from Titan and the orbiting Cassini as they conduct this chemical analysis of the moon’s atmosphere.

ESA describes the Cassini-Huygens mission as “the most ambitious effort in planetary space exploration ever mounted.” The Huygens probe was the first ever to land on a world in the outer solar system.