Saturn’s largest moon, Titan, is of particular interest to scientists because of its unusually Earth-like qualities. Prior to the arrival of NASA’s Cassini spacecraft, Titan was difficult to study because it is shrouded in a thick golden haze of photochemical smog that obscured its surface. Observations gathered by this instrument have transformed investigations of this curious moon, and now a novel set of laboratory experiments has teased out even more information.
Using Cassini data, a team of NASA scientists has got tantalizingly close to recreating an unknown material discovered in Titan’s hazy atmosphere, furthering our knowledge of its composition.
This unidentified material was detected using Cassini’s Composite Infrared Spectrometer which collects spectral data in far-infrared regions. The signature of this material suggested that it was composed of several different ingredients, but what precisely these were remained a mystery.
In order to figure out the possible constituents, scientists used a trial and error method of combining different mixtures of gases in a chamber and seeing what came out. The team knew that if they could get the concoction right, then under the correct conditions it should be possible to recreate the unknown material. Although this may sound relatively simple, given the number of possible combinations this was no mean feat.
The team started off their experiments by combining the two most abundant gases in Titan’s atmosphere, nitrogen and methane, but the resulting mixtures never matched up with the signature picked up by Cassini. So the team experimented by throwing something else into the mix; aromatic hydrocarbons. These are hydrocarbons that contain one or more benzene ring. Since these are partly responsible for Titan’s burnt orange color this seemed logical.
The researchers began with the simplest aromatic hydrocarbon, benzene, which has been previously detected in Titan’s atmosphere and then worked their way through a list of closely related aromatic compounds.
They discovered the best spectral match to the Cassini data when they added aromatic hydrocarbons containing nitrogen, which are part of a subgroup known as polycyclic aromatic nitrogen heterocycles. These are polycyclic aromatic (contain more than 1 aromatic ring) hydrocarbons where carbon atoms have been replaced by nitrogen.
“Now we can say that this material has a strong aromatic character, which helps us understand more about the complex mixture of molecules that makes up Titan’s haze,” said planetary scientist Melissa Trainer in a news-release.
Although the spectral signatures were not identical when the team aligned them, they were strikingly similar which suggested that the scientists were very close to the right combination.
“This is the closest anyone has come, to our knowledge, to recreating with lab experiments this particular feature seen in the Cassini data,” said co-lead author of the study Joshua Sebree.
The team will now continue to play with the experimental conditions in order to hopefully yield a better fit to the Cassini signature.
“With the combination of laboratory experiments and Cassini data, we gain an understanding of just how complex and wondrous this Earth-like moon really is,” said Cassini Deputy Project Scientist Scott Edgington.