Cassini finds ingredient of plastic on Titan
Sen—The Cassini spacecraft has detected propylene, a chemical used to make household plastic items, on Saturn's moon Titan. It is the first definitive detection of the plastic ingredient on any moon or planet, other than Earth.
Cassini's composite infrared spectrometer (CIRS) that measures the infrared light, or heat radiation, emitted from Saturn and its moons, identified a small amount of propylene in Titan's lower atmosphere.
"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, and lead author of the paper. "That plastic container at the grocery store with the recycling code 5 on the bottom, that's polypropylene."
CIRS can identify a particular gas glowing in the lower layers of the atmosphere from its unique thermal fingerprint. The challenge is to isolate this one signature from the signals of all other gases around it.
The detection of the chemical fills in a gap in Titan observations that dates back to the first-ever close flyby of this moon in 1980 by NASA's Voyager 1 spacecraft. Voyager identified many of the gases in Titan's hazy brown atmosphere as hydrocarbons, chemicals that primarily make up petroleum and other fossil fuels on Earth.
On Titan, hydrocarbons form as sunlight breaks apart methane, the second-most plentiful gas in that atmosphere. These freed fragments can then link up to form chains with two, three or more carbons. The family of chemicals with two carbons includes the flammable gas ethane. Propane, a common fuel for portable stoves, belongs to the three-carbon family. Voyager 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.
Researchers discovered more and more chemicals in Titan's atmosphere using ground and space based instruments, but propylene 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," 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."
"I am always excited when scientists discover a molecule that has never been observed before in an atmosphere," said Scott Edgington, Cassini's deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena. "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."