A closer look at Titan's chemical factory

Posted by TG Daily Staff


Essentially, the atmosphere is a productive "factory," cranking out hydrocarbons that rain down on Titan's icy surface. This cloaks the planet in soot and, with a brutally cold surface temperature of approximately minus 270 degrees Fahrenheit, forms lakes of liquid methane and ethane.

A closer look at Titan's chemical factoryHowever, the most important raw ingredient in this chemical factory - methane gas, a molecule made up of one carbon atom joined to four hydrogen atoms – should not last for long because it's being continuously destroyed by sunlight and converted to more complex molecules and particles.   

So how longs has this "factory" been operating? Well, several new studies, using data based on ESA and NASA research, attempt to estimate how much "heavy" methane containing rare isotopes is present in Titan's atmosphere.


By modeling how the concentration of heavy methane changes over time, the scientists attempted to measure just how long Titan's chemical factory has been running.

"Under our baseline model assumptions, the methane age is capped at 1.6 billion years, or about a third the age of Titan itself," said Conor Nixon who is stationed at NASA Goddard. "However, if methane is also allowed to escape from the top of the atmosphere, as some previous work has suggested, the age must be much shorter - perhaps only 10 million years - to be compatible with observations."

Of course,  both of these scenarios assume methane entered the atmosphere in a single burst of outgassing, probably from the restructuring of Titan's interior as heavier materials sank towards the center and lighter ones rose toward the surface.

"[Yet], if the methane has been continuously replenished from a source then its isotopes would always appear 'fresh' and we can't restrict the age in our model," Nixon added.   


Kathleen Mandt of the Southwest Research Institute, San Antonio, Texas, also modeled the time-evolution of methane. In Mandt's paradigm, the concentration of heavy methane is determined from measurements by Cassini's ion and neutral mass spectrometer, which counts molecules in the atmosphere of different masses (weights).   Measurements made by the Huygens gas chromatograph mass spectrometer, which also counts molecules of different masses, were used to constrain the impact of escape on the heavy methane in the atmosphere.


Both of the above-mentioned theories seem to confirm Titan's methane atmosphere must have formed long after Titan itself. Interestingly enough, previous work analyzing the evolution of Titan's interior indicated the last major methane eruption occurred 350 million to 1.35 billion years ago, while crater counting put the age of the current surface at 200 million to one billion years.   However, the most recent theories - for the first time - estimates the methane age from the atmosphere itself at less than one billion years.