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[ Music ]

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 I'm Conor Nixon, I'm a planetary scientist at NASA's Goddard Space Flight Center,

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and I study the atmospheric composition of the outer planets.

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Titan is Saturn's largest moon, it's actually the second-largest moon in the solar system,

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and it's the only moon in the solar system that has a large and substantial atmosphere,

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and that atmosphere in some respects is really similar to that of the Earth, being composed mainly of nitrogen, but in other respects it's really different.

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It has methane as the second-most abundant gas, and that takes the same role as water vapor in the Earth's atmosphere.

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It evaporates from the surface, it forms clouds, and then rains down again

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and in fact forms lakes that we see at Titan's north pole, including ethane and propane and all sorts of complex chemicals.

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We also see these vast dune fields at the equator, which are not made of silicates as they are on the Earth but actually made of organic substances,

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essentially plastics which have actually sedimented from the atmosphere

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and are being blown around into dune fields the same as we'd see on a desert on the Earth.

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Back in 1980 when Voyager 1 flew by Titan and made the first close encounter with that moon,

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it discovered many new chemical species in the atmosphere, and a lot of these are what we call hydrocarbons,

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which are composed of two types of atom, carbon and hydrogen.  And these are derived from methane after the methane is broken apart by sunlight

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it forms into longer and longer chain molecules.  So you can add first two carbons together to make a family of molecules,

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and you can also form three carbons together to form a heavier family of molecules.

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So it was actually very mysterious that Voyager only discovered the heaviest and the lightest members of the three carbon family,

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but it didn't find the middle member of the family, propylene, that was missing.

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So NASA has this wonderful flagship spacecraft called Cassini which is currently orbiting Saturn,

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and it's making multiple close flybys of Titan.  Now in visible light, Titan appears quite bland and featureless just like an orange globe,

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but Cassini has techniques to peer through that haze, including the Composite Infrared Spectrometer or CIRS,

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which can look at the heat coming from the atmosphere and split it apart into its different frequencies,

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and this forms a characteristic pattern of peaks, which give the characteristic signatures of different molecules.

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And through this we can detect which molecules are in the atmosphere, and we see all the molecules that were previously discovered by Voyager.

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But we're also able to look for new molecules, and in fact, buried within the signatures of these more abundant molecular species

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we saw a very small spike which was due to a new species which had not been seen before,

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and in fact this was propylene, and we saw it at multiple altitudes in Titan's atmosphere.

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When we added all the signal together, we had more than 99% confidence that we were discovering a new molecule.

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[ Music, wind blowing ]

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So this object I have right here, this is polypropylene.

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This is a plastic that we use on the Earth in everyday household objects such as this plastic tub here,

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and if we turn it over on the bottom, we find a symbol with the number 5 that says PP, polypropylene.

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This is the propylene that we found on Titan, but polymerized, that means that the molecule is formed into long chains,

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and when these chains are tangled together it forms a hard, clear plastic that we use in many household objects.

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So that was really fun for me to realize that something that we'd discovered in space was in fact something that I was touching every day on the Earth.

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So the discovery of propylene on Titan is really exciting.

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First of all, it completes this chemical family where we had this missing link dating thirty-two years back to Voyager,

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but also, it shows that there's much more there still in Titan's atmosphere to be discovered.

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Some people think that Titan is similar to the prebiotic Earth long ago, when the molecules were forming the basis of life.

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And we don't know what we're going to find on Titan if we send back further spacecraft with new instruments, more sensitive instruments,

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if some of the molecules on Titan could be similar to the basis of life on Earth.

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[ Music, satellite beeping ]