Future and its syndication partners may earn a commission when you make a purchase through links to our articles.
Saturn’s moon Titan seen beyond the planet’s rings. In the foreground is the small moon Epimetheus. . | Credits: NASA / JPL / Space Science Institute.
The rules of chemistry on Saturn’s largest moon Titan may have to be rewritten thanks to a new discovery that shows how frozen hydrogen cyanide crystals can mix with liquid hydrocarbons in a combination never before possible.
Experiments at NASA Jet Propulsion Laboratory (JPL) in Southern California, along with computer simulations by researchers at Chalmers University of Technology in Sweden, have shown how liquid ethane and methane molecules fill seas and lakes. Titancan mix with hydrogen cyanide crystals, which is frozen in the moon’s cold temperature of minus 179 degrees Celsius.
Hydrogen cyanide is described as a polar molecule in the sense that one side of it has a positive electrical charge and the other has a negative charge. This means that it prefers to bond with other polar molecules that attract opposite charges.
On the other hand, methane and ethane, which are both hydrocarbon compounds (that is, they are composed of hydrogen and carbon atoms), are non-polar molecules, meaning that their electrical charge is symmetrical, with positive and negative charges on both sides of their molecular structure.
Generally, polar and non-polar substances do not mix. It’s a bit like an oil that stays separate from water.
Hydrogen cyanide is formed in Titan’s atmosphere by reaction with ultraviolet light from the sunwhich breaks down hydrocarbons and converts them into other molecules. Given that non-polar hydrocarbons are common throughout Titan’s atmosphere and surface, JPL scientists wanted to know what happens to hydrogen cyanide after it is created. However, their laboratory experiments mixing hydrogen cyanide with methane and ethane at minus 292 degrees Fahrenheit (minus 180 degrees Celsius) produced some surprising results that they did not understand. So they turned to chemist Martin Rahm and his group at Chalmers, who had previous experience using hydrogen cyanide at low temperatures, for answers.
“This led to an interesting theoretical and experimental collaboration between Chalmers and NASA,” Rahm said. statement. “The question we asked ourselves was a bit crazy: could the measurements be explained by a crystal structure in which methane or ethane is mixed with hydrogen cyanide? This goes against the chemical rule of like dissolves like, which basically means that it shouldn’t be possible to combine these polar and non-polar substances.”
Rahm’s computer simulations found that methane and ethane can penetrate the frozen crystal lattice of hydrogen cyanide, forming a new and stable structure called a “co-crystal”.
“This can happen at very low temperatures, like on Titan,” Rahm said. “Our calculations predicted not only that the unexpected mixtures are stable under Titan conditions, but also light spectra that agree well with NASA’s measurements.”
Titan is the only moon in the world solar system have a thick atmosphere, and its hydrocarbon chemistry is similar to the prebiotic soup that scientists believe existed Earth before life begins. Although Titan’s low temperatures seem to prevent the chemical reactions that could lead to life as we know it, Titan’s astrobiological is valuable as a starting point for presenting what the molecular inventory might have been on the early Earth. Despite its toxicity to life now, hydrogen cyanide is one of the building blocks of amino acids used in proteins and the nucleobases RNA and DNA.
“Hydrogen cyanide is found in many places the universefor example, in large dust clouds, in the atmospheres and interiors of planets comets“, Rahm said. “The findings of our study can help us understand what happens in other cold spaces. And we can learn whether other non-polar molecules can also enter hydrogen cyanide crystals and, if so, what this might mean for pre-life chemistry.
Either way, the findings point to an even closer relationship between Titan’s atmosphere, its frozen surface ice dunes, and its lakes and seas methane and ethane than anyone expected. When in 2034 it’s coming to Titan, NASA’s new rotorcraft is called Dragonflywill stop on the surface and take samples of materials, including hydrogen cyanide ice, where they can test new results and look for even more complex and unexpected chemistry.
The findings were published in July in the journal PNAS.