Low-density amorphous ice is one of the most prevalent solid materials in the universe and plays a crucial role in deciphering numerous well-known anomalies of liquid water. Despite its significance and discovery nearly 90 years ago, its structure remains a topic of debate. In a recent study, researchers from the University of London and Cambridge found that prior computer simulations of low-density amorphous ice were influenced by a disturbed structure where the ice was not entirely amorphous. Instead, it contained small crystals measuring 3 nm in width, slightly wider than a single DNA strand. In their experimental studies, actual samples of amorphous ice, which formed through different methods, were recrystallized (i.e., warmed up). They observed that the resulting crystal structure varied based on the method used to generate the amorphous ice. The researchers concluded that if the ice was completely disordered, it would not retain any imprint of its previous shape.
Low-density amorphous ice structure: Many small crystals (white) are hidden in the amorphous material (blue). Image credits: Michael B. Davis, UCL & Cambridge University.
“We now have a solid understanding of what the most common ice structures in the universe look like at the atomic level,” states Dr. Michael Davis, a researcher at the University of London and Cambridge.
“This is significant because ice is involved in numerous cosmological processes, including planet formation, galaxy evolution, and the movement of matter throughout the universe.”
For their investigation, Dr. Davis and his colleagues utilized two computer models of water.
They simulated the freezing of water molecules in these virtual “cages” by cooling to -120 degrees Celsius (-184 degrees Fahrenheit) at various rates.
These different cooling rates affected the proportions of crystalline and amorphous ice produced.
The researchers determined that low-density amorphous ice, as evidenced by X-ray diffraction studies, appears to align with a mixture of up to 20% crystallinity and 80% amorphous structure (i.e., researchers fired X-rays at ice and analyzed the deflection patterns).
Using an alternative method, they created a large “box” filled with numerous small ice crystals tightly packed together.
The simulation then disordered the regions between the ice crystals, resulting in structures remarkably similar to those obtained from the initial approach of 25% crystalline ice.
In additional experimental efforts, scientists generated actual low-density amorphous ice samples through various methods, including deposits of water vapor onto extremely cold surfaces (mimicking how ice forms on interstellar dust) and from high-density amorphous ice (ice crushed at very low temperatures).
These amorphous ice samples were then gently heated to provide energy for the formation of crystals.
They noted variations in the structure of the ice depending on its origin, particularly regarding the arrangement of molecules in a hexagonal (6x) formation.
This provided indirect evidence that low-density amorphous ice contained crystalline constituents.
Should it be entirely disordered, the ice would lack any memory of its prior form.
The findings raised further inquiries about the nature of amorphous ice, such as whether crystal size varies based on the formation method, and whether truly amorphous ice is achievable.
“Water is essential to life, yet our understanding is still incomplete,” remarked Professor Michael Ryde from Cambridge University.
“Amorphous ice may be key to explaining many anomalies observed in water.”
“Ice holds potential as a high-performance material in space,” added Dr. Davis.
“It can shield spacecraft from radiation and supply fuel in the form of hydrogen and oxygen.”
“Understanding the various structures and properties is critical.”
Moreover, this research touches upon a speculative theory regarding the origins of life on Earth.
This theory posits that life’s building blocks were transported here on an icy comet, known as Panspermia.
“Our findings indicate that this ice might be a suboptimal transport medium for these biological molecules,” stated Dr. Davis.
“This is due to the reduced space available for partial embedding of these components in the crystal structure.”
“Nonetheless, the theory could still hold merit, as there are amorphous regions within the ice capable of storing and concealing life’s building blocks.”
“Ice on Earth captivates our curiosity due to our warm climate,” observed University College professor Christophe Salzmann from the University of London.
“You can see the intricate order of snowflakes in their symmetry.”
“Ice elsewhere in the universe has long been viewed as a frozen snapshot of liquid water: a disordered arrangement that is fixed in place. Our findings suggest that this perception is not entirely accurate.”
“Our results also prompt questions regarding the properties of amorphous materials in general.”
“Such materials are vital in advanced technologies.”
“For instance, fiberglass used for data transmission must be amorphous or disordered to function.”
“If these materials contain small crystals, their performance can potentially be enhanced by removing them.”
The findings were documented in a paper published today in the journal Physical Review B.
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Michael Benedict Davis et al. 2025. Low-density amorphous ice contains crystalline ice grains. Phys. Rev. B 112, 024203; doi:10.1103/PhysRevB.112.024203
Source: www.sci.news
