Titan offers great motivation for the detailed study of organic chemistry in unconventional conditions. Nonpolar hydrocarbons such as ethane and methane exist on this Saturnian moon in plentitude, alongside one of the most prebiotically relevant and polar small molecules in existence — hydrogen cyanide (HCN). New research provides evidence for the intermixing of these exceptionally polar opposites at low temperatures, forming structures that defy conventional chemical expectations.
An artistic rendering of Kraken Mare, a large liquid methane sea on Titan. Image credit: NASA’s John Glenn Research Center.
Hydrogen cyanide is widespread in astrochemical environments, having been identified in the interstellar medium and on various bodies such as comets, planets, moons, and dwarf planets.
This molecule is the second-most abundant product expected from the atmospheric chemistry of Titan.
“These are very exciting findings that can help us understand something on a very large scale, a moon as big as the planet Mercury,” said Dr. Martin Rahm, a researcher at Chalmers University of Technology.
In their lab experiments, Dr. Rahm and his colleagues mixed hydrogen cyanide with methane and ethane at temperatures as low as 90 K (about minus 180 degrees Celsius).
At these temperatures, hydrogen cyanide is a crystal, and methane and ethane are liquids.
When the researchers studied such mixtures using laser spectroscopy, a method for examining materials and molecules at the atomic level, they found that the molecules were intact, but that something had still happened.
To understand what, they used large scale computer simulations to test thousands of different ways of organizing the molecules in the solid state.
They found that hydrocarbons had penetrated the crystal lattice of hydrogen cyanide and formed stable new structures known as co-crystals.
“The discovery of the unexpected interaction between these substances could affect how we understand the Titan’s geology and its strange landscapes of lakes, seas and sand dunes,” Dr. Rahm said.
“In addition, hydrogen cyanide is likely to play an important role in the abiotic creation of several of life’s building blocks, for example amino acids, which are used for the construction of proteins, and nucleobases, which are needed for the genetic code.”
“So our work also contributes insights into chemistry before the emergence of life, and how it might proceed in extreme, inhospitable environments.”
The results were published in July 2025 in the Proceedings of the National Academy of Sciences.
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Fernando Izquierdo-Ruiz et al. 2025. Hydrogen cyanide and hydrocarbons mix on Titan. PNAS 122 (30): e2507522122; doi: 10.1073/pnas.2507522122