At the 2019 Astrobiology Science Conference being held in Bellevue, Washington, Morgan Cable of NASA’s JPL presented the results of a study conducted with other researchers on Titan, Saturn’s largest moon. This team recreated in lab some conditions existing in the lakes of methane and other hydrocarbons of Titan, discovering that a co-crystal of solid acetylene and butane could be produced with the formation of ring-shaped deposits around those lakes similarly to salt deposits which are produced when water evaporates in the Earth’s seas. Those co-crystals could be used by exotic life forms in a way similar to carbon dioxide on Earth.
Titan has long been known for the complex chemical reactions that take place in its atmosphere and in its methane lakes, with the possibility that complex molecules are also formed. The conditions on that moon, a consequence of the very low temperature, are really alien and yet in some ways similar to the Earth’s ones, to the point that they led to hypothesize the existence of really exotic life forms, but so far no research has given conclusive answers.
On Earth, acetylene and butane exist in gaseous form but at the temperatures existing on Titan they’re solid and can combine to form a co-crystal, a crystal structure composed of at least two components (the definition is controversial). This result was obtained by reproducing in lab the conditions existing in the lakes near Titan’s equator, where the observations conducted by the Cassini space probe showed signs left by evaporated materials.
A cryostat used to reach Titan’s temperatures was filled with liquid nitrogen and then slightly heated to evaporate it to become like the gas that makes up most of that moon’s atmosphere. They then added methane, ethane and other carbon-containing molecules observing what happened.
The first result was the formation of benzene crystals, another compound common on Earth as part of gasoline. However, under Titan’s conditions benzene molecules allowed ethane molecules inside, forming a co-crystal.
The next result was the formation of acetylene and butane co-crystals. According to Morgan Cable, Titan’s composition suggests that they’re much more common than benzene crystals. In the climate existing on that moon, acetylene and butane co-crystals can form rings around lakes when liquid hydrocarbons evaporate and minerals form deposits, as happens on Earth with salt deposits.
For now this is a result obtained in lab but Titan has a thick and hazy atmosphere that makes surface observations really difficult. A new mission to send a space probe to Saturn system could test this and other results but even in the best-case scenario it will take several years for it to happen. The interest about Titan still remains high for the activity existing on that moon despite its very low temperatures.
Edit. NASA has just announced the Dragonfly mission to send a lander capable of moving on the surface of Titan. Its launch is scheduled for 2026, the arrival for 2034.