🧪 How Titan could rewrite the history of life in the Universe

The rules of chemistry on Titan, Saturn's largest moon, may well be rewritten. As a result, the chemistry of life could also be rewritten.

An unexpected discovery reveals how frozen crystals of a toxic compound, hydrogen cyanide, can mix with liquid hydrocarbons like methane and ethane, forming stable structures under extreme conditions. This interaction, previously thought impossible, opens new perspectives on prebiotic chemistry in the Solar System and beyond.


Experiments conducted at NASA's Jet Propulsion Laboratory, combined with computer simulations by Chalmers University of Technology in Sweden, have allowed observation of this surprising phenomenon. Researchers worked at temperatures close to those on Titan, around -180 °C (-292 °F), where hydrogen cyanide exists as solid crystals.


In the laboratory, they found that methane and ethane, although nonpolar, could penetrate the crystal structure of hydrogen cyanide, creating what is called a "co-crystal." This unexpected stability challenges the chemical principle that polar and nonpolar substances do not mix.

Hydrogen cyanide is a polar molecule, meaning it has a positively charged side and a negatively charged side, normally favoring bonds with other polar molecules. In contrast, methane and ethane are nonpolar hydrocarbons, with a symmetrical distribution of electrical charges. On Earth, this difference explains why oil and water do not mix. Yet on Titan, simulations have shown that these compounds can associate, forming stable hybrid crystal structures in the moon's icy environment.

This discovery has major implications for understanding prebiotic chemistry, that is, the chemical reactions that may have preceded the emergence of life. Hydrogen cyanide is a key precursor to amino acids, the building blocks of proteins, and to the nucleobases of RNA and DNA. Although toxic to current life, it may have played an essential role in forming the first biological molecules on early Earth. Titan, with its hydrocarbon lakes and rich atmosphere, offers a natural laboratory to study these processes.

NASA's Dragonfly mission, scheduled to arrive at Titan in 2034, will verify these results by collecting samples of hydrogen cyanide ice from the surface. This mission, equipped with a rotorcraft, will explore various sites to analyze the chemistry of this moon. Researchers hope to discover other unexpected interactions between polar and nonpolar molecules, broadening our understanding of icy environments in the Universe.

Polar and nonpolar molecules

Polar molecules, like hydrogen cyanide, have an uneven distribution of electrical charges, creating a positive pole and a negative pole. This polarity favors interactions with other polar molecules through electrostatic attraction, which explains why they often dissolve in polar solvents like water.


Nonpolar molecules, such as methane and ethane, have symmetrical charge distributions, making them poorly compatible with polar substances. Generally, they prefer to associate with other nonpolar molecules, a principle summarized by the saying "like dissolves like."

On Titan, the discovery of mixtures between these two types of molecules challenges this rule. The extreme low temperatures, around -180 °C (-292 °F), allow methane and ethane to penetrate hydrogen cyanide crystals, forming stable co-crystals. This interaction is facilitated by the crystal structure, which can accommodate nonpolar molecules in its interstices.

This exception paves the way for new research on molecular mixtures in cold environments, such as interstellar clouds or comets, where similar reactions might occur.

Prebiotic chemistry and the origins of life

Prebiotic chemistry studies the chemical reactions that may have led to the emergence of life on Earth about 4 billion years ago. It focuses on the formation of complex organic molecules from simple compounds under natural conditions.

Hydrogen cyanide is considered an important precursor in this process. It can react with other molecules to form amino acids, which are the basic units of proteins, essential for life. Similarly, it is involved in the synthesis of nucleobases, components of RNA and DNA.

Titan, with its hydrocarbon lakes and nitrogen-rich atmosphere, resembles a frozen version of early Earth. Interactions between hydrogen cyanide and hydrocarbons could simulate key steps of prebiotic chemistry there, despite the hostile temperatures.

By understanding these mechanisms on Titan, scientists hope to clarify how life could have emerged on Earth and whether similar processes are possible elsewhere in the Universe, for example on exoplanets or other icy moons.