Scientists Simulate Complex Chemistry of Titan’s Atmosphere

Saturn’s moon Titan is a fascinating celestial object, and not just because it orbits another planet. Titan has more than twice as much surface area as our moon and is one of two known objects with stable bodies of liquid on the surface — the other is Earth. Although, on Titan, it’s liquid hydrocarbons instead of water. Titan is also the only moon we know of with an atmosphere, and a new study aims to explain why it’s so full of complex hydrocarbons.

Titan’s atmosphere is 1.5 times a dense as Earth’s and consists mainly of nitrogen along with some methane, hydrogen, and trace amounts of complex molecules that could be precursors to life as we know it. Titan is also what’s known as a “super-rotator,” meaning the atmosphere rotates significantly faster than the planet. All in all, it’s not a very pleasant place to be.

The conventional wisdom is that high temperatures are necessary to create the complex mix of hydrocarbons on Titan, but of course, it’s very chilly on Titan with an average temperature of -292 degrees Fahrenheit (-180 Celsius). Researchers are particularly interested in the presence of multi-ringed hydrocarbon molecules called polycyclic aromatic hydrocarbons (PAHs) in Titan’s atmosphere. The team led by Ralf Kaiser from the University of Hawaii suggests that a combination of two gases in Titan-like conditions could generate PAHs without high temperatures.

Researchers mixed an unstable two-ringed PAH called a naphthyl radical with a simple hydrocarbon called vinylacetylene. The result was a three-ringed PAH without high temperatures, and both naphthyl radicals and vinylacetylene likely exist on Titan. These PAHs could form much more complex molecules that give rise to new forms of life.

If ringed hydrocarbons don’t require high-energy conditions, they could be much more common throughout the universe than we thought. It’s difficult to know, though, because they are extremely difficult to detect in space. In addition to the practical experiments, the team also ran the numbers to show how these reactants could come together to form complex molecules in other low-temperature conditions. They found the reaction was very efficient, requiring no outside energy source.

This research could help inform how scientists will study Titan’s atmosphere in the future. There are several proposed NASA missions to explore Titan, but nothing is on the books yet.

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