Cassini spacecraft finds plastic ingredient on Saturn moon

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U.S. space agency NASA said Monday its Cassini spacecraft has detected propylene, a chemical used to make food-storage containers, car bumpers and other consumer products, on Saturn's moon Titan.

Cassini identified a small amount of propylene in Titan's lower atmosphere, marking "the first definitive detection of the plastic ingredient" on any moon or planet, other than Earth, NASA researchers said in the journal Astrophysical Journal Letters.

"This chemical is all around us in everyday life, strung together in long chains to form a plastic called polypropylene," lead author Conor Nixon, a planetary scientist at NASA's Goddard Space Flight Center, said in a statement. "That plastic container at the grocery store with the recycling code 5 on the bottom -- that's polypropylene."

The researchers said they identified the chemical using Cassini 's Composite Infrared Spectrometer (CIRS), an instrument that measures the infrared light, or heat radiation, emitted from Saturn and its moons in much the same way our hands feel the warmth of a fire.

The discovery fills in a mysterious gap in Titan observations during the Voyager 1 spacecraft's close flyby of this moon in 1980, NASA said. At that time, Voyager identified many of the gases in Titan's hazy brownish atmosphere as hydrocarbons, the chemicals that primarily make up petroleum and other fossil fuels on Earth.

The researchers said hydrocarbons form on Titan after sunlight breaks apart methane, the second-most plentiful gas in that atmosphere. The newly freed fragments can link up to form chains with two, three or more carbons. The two-carbon family includes the flammable gas ethane, while propane, a common fuel for portable stoves, belongs to the three-carbon family.

Voyager detected all members of the one- and two-carbon families in Titan's atmosphere. From the three-carbon family, the spacecraft found propane, the heaviest member, and propyne, one of the lightest members. But the middle chemicals, one of which is propylene, were missing.

As researchers continued to discover more and more chemicals in Titan's atmosphere using ground- and space-based instruments, propylene was one that remained elusive. Cassini's mass spectrometer, a device that looks at the composition of Titan's atmosphere, had hinted earlier that propylene might be present in the upper atmosphere. However, the researchers were unable to make a definitive declaration based on spectrometry data.

"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 scientist and principal investigator for CIRS. "This success boosts our confidence that we will find still more chemicals long hidden in Titan's atmosphere."

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