Planetary scientists using the Composite InfRared Spectrometer aboard NASA/ESA’s Cassini spacecraft have detected propylene in the lower atmosphere of the Saturn’s largest moon, Titan. This is the first detection of the plastic ingredient on any moon or planet, other than Earth.

Propylene, a chemical used to make food-storage containers and car bumpers, is the first molecule to be discovered on Titan using Cassini’s Composite InfRared Spectrometer (CIRS).

The instrument measures the infrared energy from Saturn, its rings and moons in order to study their thermal structure and composition. By isolating the same signal at various altitudes within the Titan’s lower atmosphere, scientists identified propylene with a high degree of confidence.

Dr Conor Nixon of NASA’s Goddard Space Flight Center in Greenbelt, who is a lead author of the paper published in the Astrophysical Journal Letters, said: “this chemical is all around us in everyday life, strung together in long chains to form a plastic called polypropylene.”

The detection of the propylene fills in a mysterious gap in observations of the Saturn’s moon that dates back to NASA’s Voyager 1 spacecraft and the first-ever close flyby of this moon in 1980.

Voyager 1 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 spacecraft found propane, the heaviest member of the three-carbon family, and propyne, one of the lightest members. But the middle chemicals, one of which is propylene, were missing.

As scientists continued to discover more and more chemicals in Titan’s atmosphere using ground- and space-based instruments, propylene was one that remained elusive. It was finally found as a result of more detailed analysis of the CIRS data.

“This measurement was very difficult to make because propylene’s weak signature is crowded by related chemicals with much stronger signals,” explained senior author Dr Michael Flasar, also from NASA’s Goddard Space Flight Center in Greenbelt.

“This success boosts our confidence that we will find still more chemicals long hidden in Titan’s atmosphere.”

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Bibliographic information: C. A. Nixon et al. 2013. Detection of Propene in Titan’s Stratosphere. ApJ 776, L14; doi: 10.1088/2041-8205/776/1/L14