The research team used computer simulations and experimental methods to investigate the atomic-level structure of this widespread cosmic ice. Simulations showed the ice's properties best matched experimental data when up to 25% of it was crystalline, consisting of crystals about three nanometres across embedded within an otherwise disordered matrix.
By warming real samples of low-density amorphous ice created via various methods, researchers found that the resulting crystal structure varied depending on how the ice initially formed. This retention of structural memory indicates the ice was never fully amorphous to begin with.
Lead author Dr Michael B. Davies explained, "We now have a good idea of what the most common form of ice in the Universe looks like at an atomic level. This is important as ice is involved in many cosmological processes, for instance in how planets form, how galaxies evolve, and how matter moves around the Universe."
The presence of crystalline regions also has implications for theories about the origin of life. One such idea, Panspermia, suggests life's building blocks arrived on Earth embedded in space ice. However, Davies noted that partially crystalline ice offers less internal space to trap and transport these molecules. "The theory could still hold true, though, as there are amorphous regions in the ice where life's building blocks could be trapped and stored," he added.
Professor Christoph Salzmann, a co-author from UCL Chemistry, remarked, "Our findings show [ice in space] is not entirely a snapshot of liquid water. Our results also raise questions about amorphous materials in general," pointing to potential improvements in fiber optics and other technologies if these insights into structural disorder can be applied.
The team created their simulations by cooling virtual boxes of water to -120 degrees Centigrade at different rates, observing that slower cooling allowed some crystallization. In separate trials, they simulated clusters of small ice grains with disordered boundaries, reaching similar structures. Real-world samples of amorphous ice were produced using methods like vapor deposition on cold surfaces or compressing and warming other ice forms.
These investigations revealed subtle differences in hexagonal molecular arrangements after crystallization, reinforcing the presence of crystalline components. The researchers now seek to understand whether a truly amorphous ice can exist and how its structure depends on formation conditions.
First identified in the 1930s and further characterized in later decades, amorphous ices now include low-, high-, and medium-density varieties. The medium-density form, discovered in 2023 by the same UCL-Cambridge team, matches the density of liquid water.
"Water is the foundation of life but we still do not fully understand it," said co-author Professor Angelos Michaelides. "Amorphous ices may hold the key to explaining some of water's many anomalies."
Dr Davies added that knowing the properties of ice is also crucial for space technology. "It could shield spacecraft from radiation or provide fuel in the form of hydrogen and oxygen," he said.
Research Report:Low-density amorphous ice contains crystalline ice grains
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