[ Music ]
I'm Conor Nixon, I'm a planetary scientist at NASA's Goddard Space Flight Center,
and I study the atmospheric composition of the outer planets.
Titan is Saturn's largest moon, it's actually the second-largest moon in the solar system,
and it's the only moon in the solar system that has a large and substantial atmosphere,
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.
It has methane as the second-most abundant gas, and that takes the same role as water vapor in the Earth's atmosphere.
It evaporates from the surface, it forms clouds, and then rains down again
and in fact forms lakes that we see at Titan's north pole, including ethane and propane and all sorts of complex chemicals.
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,
essentially plastics which have actually sedimented from the atmosphere
and are being blown around into dune fields the same as we'd see on a desert on the Earth.
Back in 1980 when Voyager 1 flew by Titan and made the first close encounter with that moon,
it discovered many new chemical species in the atmosphere, and a lot of these are what we call hydrocarbons,
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
it forms into longer and longer chain molecules. So you can add first two carbons together to make a family of molecules,
and you can also form three carbons together to form a heavier family of molecules.
So it was actually very mysterious that Voyager only discovered the heaviest and the lightest members of the three carbon family,
but it didn't find the middle member of the family, propylene, that was missing.
So NASA has this wonderful flagship spacecraft called Cassini which is currently orbiting Saturn,
and it's making multiple close flybys of Titan. Now in visible light, Titan appears quite bland and featureless just like an orange globe,
but Cassini has techniques to peer through that haze, including the Composite Infrared Spectrometer or CIRS,
which can look at the heat coming from the atmosphere and split it apart into its different frequencies,
and this forms a characteristic pattern of peaks, which give the characteristic signatures of different molecules.
And through this we can detect which molecules are in the atmosphere, and we see all the molecules that were previously discovered by Voyager.
But we're also able to look for new molecules, and in fact, buried within the signatures of these more abundant molecular species
we saw a very small spike which was due to a new species which had not been seen before,
and in fact this was propylene, and we saw it at multiple altitudes in Titan's atmosphere.
When we added all the signal together, we had more than 99% confidence that we were discovering a new molecule.
[ Music, wind blowing ]
So this object I have right here, this is polypropylene.
This is a plastic that we use on the Earth in everyday household objects such as this plastic tub here,
and if we turn it over on the bottom, we find a symbol with the number 5 that says PP, polypropylene.
This is the propylene that we found on Titan, but polymerized, that means that the molecule is formed into long chains,
and when these chains are tangled together it forms a hard, clear plastic that we use in many household objects.
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.
So the discovery of propylene on Titan is really exciting.
First of all, it completes this chemical family where we had this missing link dating thirty-two years back to Voyager,
but also, it shows that there's much more there still in Titan's atmosphere to be discovered.
Some people think that Titan is similar to the prebiotic Earth long ago, when the molecules were forming the basis of life.
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,
if some of the molecules on Titan could be similar to the basis of life on Earth.
[ Music, satellite beeping ]