Leeds physicists help unlock chemical secrets of Saturn’s moon Titan

Researchers have taken a significant step towards understanding the chemistry of Saturn’s largest moon, Titan – a place that may hold clues to how life began in our solar system.

In collaboration with the ISIS Neutron and Muon Source in Oxfordshire, the Leeds team, including Professor Lorna Dougan, Dr Mazin Nasralla, and Dr Harrison Laurent, revealed how ammonia – a chemical thought to be abundant in Titan’s icy crust and hidden oceans – interacts with liquid water.

Their findings, published this month in Nature Communications Chemistry, could help scientists interpret the data from NASA’s upcoming Dragonfly mission, which is due to land on Titan’s Selk crater in 2034.

Titan is a distant moon with rivers and lakes of liquid methane, a thick nitrogen atmosphere, and, beneath its frozen surface, a vast ocean that may be rich in ammonia. Because ammonia can keep water liquid at much lower temperatures, its presence could greatly expand the conditions under which life might form and survive.

Using a specialised technique called neutron diffraction, the team examined a solution of water containing 20.5% ammonia at temperatures close to freezing and at room temperature. The results showed that ammonia molecules form a distinctive “hydration shell” – a loose arrangement of water molecules around them – that includes small, ice-like patterns.

This kind of microscopic structuring has been linked to the way biological molecules, such as proteins, fold and interact in water on Earth. Seeing similar effects in ammonia-rich water highlights the potential that prebiotic chemistry – processes that precede new life – could also occur in the cold oceans of worlds like Titan, or other distant icy moons around stars in our solar system and beyond.

What's more, the team’s research sheds light on the fundamental structural properties of ammonia-water mixtures, which are relevant here on Earth in fields such as the physics of life, cryopreservation, and industrial chemistry.

Professor Dougan, from the School of Physics and Astronomy, said: “Neutron diffraction is a powerful way to investigate ammonia-water solutions as neutrons are uniquely sensitive to hydrogen, allowing for mapping of hydrogen-bonded structures with atomic precision.”

The project was funded by the Engineering and Physical Sciences Research Council and the European Research Council, with experimental work carried out on the NIMROD instrument at the ISIS facility.

Further information

• Photo, showing Titan chasing its shadow across Saturn, by NASA Hubble Space Telescope on Unsplash.
• Read “Solution structure of Titan-relevant aqueous ammonia by neutron diffraction” at Nature Communications Chemistry.
• For media enquiries, please contact Faculty Communications Manager Matt Gardner at M.D.Gardner@leeds.ac.uk.