The detection of the chemical used to make food-storage containers, car bumpers and other products is the first discovery of the plastic ingredient on any moon or planet other than Earth, NASA said in a release.
Cassini's Composite Infrared Spectrometer identified a small amount of propylene in Titan's lower atmosphere, NASA said. The instrument measures the infrared light emitted from Saturn and its moons much the same way human hands feel the warmth of a fire.
Propylene is the first molecule to be discovered on Titan using the spectrometer.
"This chemical is all around us in everyday life, strung together in long chains to form a plastic called polypropylene," said Conor Nixon, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "That plastic container at the grocery store with the recycling code 5 on the bottom -- that's polypropylene."
Cassini's mass spectrometer had suggested earlier that propylene may be present in the upper atmosphere but a positive identification wasn't made until now, NASA said.
"This new piece of the puzzle will provide an additional test of how well we understand the chemical zoo that makes up Titan's atmosphere," said Scott Edgington, Cassini's deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.