Recently, a NASA probe returned a sample from the surface of the asteroid Bennu. When they analysed the sample, they discovered amino acids and nucleotide bases (the building blocks of life) that likely formed on Bennu's parent body in the presence of ammonia-rich fluids. Scientists also believe Titan's subsurface ocean could be rich in ammonia, which is a molecule that dramatically changes liquid water's behaviour. Understanding how ammonia interacts with water under Titan-like conditions could aid the understanding of the pre-biotic chemistry of ocean worlds like Titan.
Despite decades of research into planetary ices, this is the first study to use neutron diffraction to look at these ammonia solutions.
The inspiration for this research goes back to the Cassini mission (1997-2017), which discovered plumes of ice-water off the South-pole of Encedalus, reshaping how scientists think about where in the solar system liquid water can exist. Titan is one such world, and the only moon in the solar system with a thick atmosphere. It has a surface temperature of about 94 K with a pressure similar to that on the Earth's surface.
Cassini observations show impact craters on Titan, and models suggest that an impact could produce meltwater that stays liquid for roughly 1000 years, cooling from above 273 K. This would create a temporary Earth-like fluid environment. NASA's upcoming Dragonfly mission will land on Saturn's largest moon, Titan, in 2034 but, until then, scientists must use the tools we have on Earth to study what might be happening on its surface.
In this study, the team recreated an ammonia-water mixture under conditions that are comparable to temporary impact melts on Titan and measured it using the Nimrod beamline at ISIS.
Neutrons are uniquely sensitive to hydrogen, allowing them to map hydrogen-bonded structures with atomic precision.
"These experiments were possible thanks to the rich research environment for studying liquids and disordered systems at the ISIS facility and the sample environment development which enables low temperature studies," says Lorna Dougan, University of Leeds.
Their results were not what they were expecting. They had thought that the ammonia molecule, with its strong electronegative nitrogen atom, would weaken liquid water's hydrogen bond network. Their neutron diffraction data revealed that instead, the addition of ammonia molecules to the solution enhanced the tetrahedral organisation of liquid water's hydrogen bond network leading to the formation of “ice-like-motifs". This suggests that ammonia-rich melts on Titan could maintain a surprisingly stable and structured liquid state, altering the energetic stability of the liquid water network and the physics that controls the assembly of the basic building blocks of life.
“The neutron diffraction technique has a powerful role to play in this story, and it will continue to support the new and future new observations being made in space," adds Lorna
Mazin Nasralla, lead author on the paper, hopes “People studying ocean worlds will look more deeply into how their composition changes and start to think about the implications of different molecules forming and interacting in water. The way to explore this is by using the most advanced experimental techniques we have".
This perspective reminds us that exploring distant oceans isn't just about discovery but also about understanding the chemistry that could one day reveal signs of life. By combining curiosity with the best tools science has to offer, we move closer to answering one of the humanity's greatest questions: Are we alone in the universe?
For more information:
Research Paper - Nasralla, M., Laurent, H., Alderman, O.L.G. et al. Solution structure of Titan-relevant aqueous ammonia by neutron diffraction. Commun Chem 8, 227 (2025). https://doi.org/10.1038/s42004-025-01599-8.
NASA probe OSIRIS-REx - Glavin, D. P. et al. Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu. Nat. Astron. 9, 199–210 (2025)
Cassini mission (1997-2017) - Spilker, L. Cassini-Huygens' exploration of the Saturn system: 13 years of discovery. Science 364, 1046–1051 (2019).
