A new study has shown that Titan, Saturn’s biggest moon, may allow substances that normally cannot mix on Earth to combine.
Scientists from Chalmers University of Technology in Sweden and NASA found that extreme cold conditions on Titan could let polar and nonpolar molecules mix.
This includes polar hydrogen cyanide and nonpolar hydrocarbons like methane and ethane.
Researchers simulated Titan’s surface and atmosphere in laboratory conditions. They used spectroscopic analysis to examine how molecules behave in extremely low temperatures. The study was published in PNAS.
They found that hydrogen cyanide and hydrocarbons can co-crystallise in solid form. This surprising combination appears possible because intermolecular forces within hydrogen cyanide crystals get stronger at such low temperatures. This allows the nonpolar molecules to slip into the crystal structure.
Martin Rahm, Associate Professor at Chalmers' Department of Chemistry and Chemical Engineering and the study's lead author, said that the findings were very exciting and could help scientists understand something on a large scale – a moon as big as the planet Mercury.
The principle of “like dissolves like” usually keeps polar molecules, such as water, and nonpolar molecules, such as oil, separated. On Earth, polar molecules have an uneven charge distribution. Nonpolar molecules have a balanced charge. This difference means they usually repel each other. But Titan’s surface temperatures can drop to -183 degrees C.
The scientists say these extreme conditions could lead to different chemical behaviour.
Rahm said that the discovery of the unexpected interaction between those substances could influence how Titan’s geology was understood, as well as its unusual landscape of lakes, seas, and sand dunes.
He explained that hydrogen cyanide was also likely to play an important role in the abiotic creation of several of life’s building blocks, such as amino acids, which are used to construct proteins, and nucleobases, which are required for the genetic code. Therefore, he said their work also contributed insights into prebiotic chemistry and how such processes might unfold in extreme and inhospitable environments.
He stated that this had led to an exciting theoretical and experimental collaboration between Chalmers and NASA.
According to him, the team had asked themselves whether the measurements could be explained by a crystal structure in which methane or ethane was mixed with hydrogen cyanide – an idea he admitted sounded “a bit crazy,” since it contradicted the basic chemical principle that “like dissolves like,” which implied that polar and non-polar substances should not be able to combine.