The tricarbon molecule (C3) is likely produced in the upper atmosphere of Titan by the reaction of abundant acetylene with atomic carbon.
This view of Titan is among the last images NASA’s Cassini spacecraft sent to Earth before it plunged into the giant planet’s atmosphere. Image credit: NASA / JPL-Caltech / Space Science Institute.
Among our Solar System’s more than 150 known moons, Saturn’s largest moon Titan is the only one with a substantial atmosphere.
And of all the places in the Solar System, Titan is the only place besides Earth known to have liquids in the form of rivers, lakes and seas on its surface.
Titan is larger than the planet Mercury and is the second largest moon in our Solar System. Jupiter’s moon Ganymede is just a little bit larger (by about 2%).
Titan’s atmosphere is made mostly of nitrogen, like Earth’s, but with a surface pressure 50% higher than Earth’s.
Titan has clouds, rain, rivers, lakes and seas of liquid hydrocarbons like methane and ethane.
“Home to a thick and chemically diverse atmosphere, Titan stands out among the giant planet’s icy satellites, as one of the most thoroughly studied objects in the Solar System,” said Dr. Rafael Silva, an astronomer with Observatório Astronómico de Lisboa and the University of Lisbon.
“Titan’s atmosphere works like a planetary-sized chemical reactor, producing many complex carbon-based molecules.”
“Of all the atmospheres we know in the Solar System, it is the most similar to the one we think existed on the early Earth.”
“Methane, which on Earth is a gas, provides information about geological processes and potentially about biological processes.”
“It is a molecule that does not survive long in the atmospheres of Earth or Titan because it is quickly and irreversibly destroyed by solar radiation.”
“For this reason, on Titan, methane must be being replenished by geological processes, such as the release of underground gas.”
In their study, Dr. Silva and his colleagues analyzed high resolution visible spectra of Titan obtained with the UVES high-resolution visible and ultraviolet spectrograph on ESO’s Very Large Telescope.
They were able to identify 97 absorption lines for methane as well as one for the tricarbon molecule.
“Even in high-resolution spectra, methane absorption lines are not strong enough with the amount of gas we can have in a lab on Earth,” Dr. Silva said.
“But on Titan we have an entire atmosphere, and the path that light travels through the atmosphere can be hundreds of km long.”
“This makes the different bands and lines, which have a weak signal in laboratories on Earth, very evident on Titan.”
“In the Solar System, the tricarbon molecule, which manifests itself as a bluish emission, was until now only known in the material surrounding the nucleus of a comet.”
“The absorption lines on Titan that we associated with tricarbon are few and of low intensity, despite being very specific to this type of molecules, so new observations will be carried out in the future to try to confirm this detection.”
“The more we know about the different molecules that participate in the chemical complexity of Titan’s atmosphere, the better we will understand the type of chemical evolution that may have allowed, or be related to, the origin of life on Earth.”
“Some of the organic matter that contributed to the origin of life on Earth is thought to have been produced in its atmosphere by processes relatively similar to those we observed on Titan.”
A paper on the findings was published in the journal Planetary and Space Science.
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Rafael Rianço-Silva et al. 2024. A study of very high resolution visible spectra of Titan: Line characterisation in visible CH4 bands and the search for C3. Planetary and Space Science 240: 105836; doi: 10.1016/j.pss.2023.105836
