NASA's Cassini spacecraft has detected propylene, a key ingredient in plastics, on Saturn's moon Titan.
This is the first time the chemical has been definitively found on any moon or planet, other than Earth. The discovery fills in what NASA called a "mysterious gap" in scientists' knowledge of the makeup of Titan's atmosphere and gives them confidence that there are more chemicals there still to discover.
Propylene is an ingredient in many consumer plastic products like car bumpers and food storage containers.
The interest lies in the small amount of propylene that was discovered in Titan's lower atmosphere by one of Cassini's scientific instruments called the the composite infrared spectrometer (CIRS), which measures the infrared light, or heat radiation, emitted from Saturn and its moons.
The instrument can detect a particular gas, like propylene, by its thermal markers, which are unique like a human fingerprint.
Scientists have a high level of confidence in their discovery, according to NASA.
"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. "That plastic container at the grocery store with the recycling code 5 on the bottom -- that's polypropylene."
The discovery gives NASA scientists the missing piece of the puzzle for determining the chemical makeup of Titan's atmosphere.
In 1980, NASA's Voyager 1 spacecraft, which has flown past Jupiter, Saturn, Uranus and Neptune, did a fly-by of Titan.
According to the space agency, 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.
Titan has a thick atmosphere, clouds, a rain cycle and giant lakes. However, unlike on Earth, Titan's clouds, rain, and lakes are largely made up of liquid hydrocarbons, such as methane and ethane.
When Titan's hydrocarbons evaporate and encounter ultraviolet radiation in the moon's upper atmosphere, some of the molecules are broken apart and reassembled into longer hydrocarbons like ethylene and propane, NASA said.
Voyager's instruments detected carbon-based chemicals in the atmosphere but not propylene. Now scientists have that piece of the puzzle.
"This measurement was very difficult to make because propylene's weak signature is crowded by related chemicals with much stronger signals," said Michael Flasar, a scientist at NASA's Goddard Space Flight Center and chief 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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