Researchers from NASA and Chalmers University have found that polar and nonpolar substances can mix on Titan's surface, defying the 'like dissolves like' principle. This occurs under the moon's extreme cold, where hydrogen cyanide forms stable crystals with methane and ethane. The finding could reshape understanding of Titan's geology and prebiotic chemistry.
Saturn's largest moon, Titan, has long intrigued scientists due to its thick nitrogen-methane atmosphere and surface conditions resembling early Earth billions of years ago. A new study reveals that in Titan's frigid environment, around 90 Kelvin (-180 degrees Celsius), hydrogen cyanide—a polar molecule abundant in the moon's atmosphere—can form co-crystals with nonpolar hydrocarbons like methane and ethane, which are liquids on the surface.
The research, led by Martin Rahm, an associate professor at Chalmers University of Technology in Sweden, began with questions about hydrogen cyanide's fate after forming in Titan's atmosphere. Collaborating with NASA's Jet Propulsion Laboratory (JPL) in California, the team conducted experiments mixing these compounds at ultra-low temperatures. Using laser spectroscopy, they observed unexpected interactions, prompting theoretical simulations at Chalmers to confirm stable co-crystal structures.
"The discovery of the unexpected interaction between these substances could affect how we understand Titan's geology and its strange landscapes of lakes, seas and sand dunes," Rahm said. He added that hydrogen cyanide likely contributes to abiotic creation of life's building blocks, such as amino acids and nucleobases, in extreme environments.
This challenges chemistry's 'like dissolves like' rule, where polar and nonpolar molecules typically separate. "I see it as a nice example of when boundaries are moved in chemistry and a universally accepted rule does not always apply," Rahm noted. The study, published in PNAS on October 16, 2025, involved researchers from Chalmers, JPL, Caltech, and Universidad Complutense de Madrid.
Titan features methane-ethane lakes, dunes, and a possible subsurface water ocean kilometers deep. NASA's Dragonfly mission, launching in 2028 and arriving in 2034, aims to explore these prebiotic processes directly. Until then, such lab insights expand knowledge of cold cosmic chemistry, including in comets and dust clouds.