According to new research by UCL and the University of Cambridge, ‘space ice’ contains tiny crystals and isn’t a completely disordered material like liquid water, as previously thought.
Space ice is different to the crystalline form of ice on Earth, and for decades, scientists have assumed it has no structure, with colder temperatures meaning it doesn’t have enough energy to form crystals when it freezes.
The new study investigated the most common form of ice in the Universe, low-density amorphous ice, which exists as the bulk material in comets, on icy moons and in clouds of dust where stars and planets form.
They found that computer simulations of this ice best matched measurements from previous experiments if the ice was not fully amorphous but contained tiny crystals (about three nanometres wide, slightly wider than a single strand of DNA) embedded within its disordered structures.
Final structure depends on how space ice originates
In experimental work, they also recrystallised (i.e., warmed up) real samples of amorphous space ice that had formed in different ways.
They found that the final crystal structure varied depending on how the amorphous ice had originated. If the ice had been fully amorphous (fully disordered), the researchers concluded, it would not retain any imprint of its earlier form.
Lead author Dr Michael Davies, who carried out the work as part of his PhD at UCL Physics & Astronomy and the University of Cambridge, said: “We now have a good idea of what the most common form of space ice 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.”
Findings help speculate about the origins of life
The findings also have implications for a speculative theory about the origins of life on Earth.
According to a theory known as Panspermia, the building blocks of life were carried here on an ice comet, with low-density amorphous ice acting as a type of space shuttle material, in which ingredients such as simple amino acids were transported.
“Our findings suggest this ice would be a less good transport material for these origin of life molecules. That is because a partly crystalline structure has less space in which these ingredients could become embedded,” Dr Davies explained.
“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.”
Co-author Professor Christoph Salzmann, of UCL Chemistry, added: “Ice on Earth is a cosmological curiosity due to our warm temperatures. You can see its ordered nature in the symmetry of a snowflake.
“Space ice has long been considered a snapshot of liquid water – that is, a disordered arrangement fixed in place. Our findings show this is not entirely true.”
He added: “Our results also raise questions about amorphous materials in general. These materials have important uses in advanced technology.
For instance, glass fibres that transport data long distances need to be amorphous, or disordered, for their function. If they do contain tiny crystals and we can remove them, this will improve their performance.”
Additional questions about the nature of amorphous ice
The research team stated that their findings raised numerous additional questions about the nature of amorphous ices – for instance, whether the size of crystals varied depending on how the amorphous ice formed, and whether a truly amorphous ice was possible.
Amorphous ice was first discovered in its low-density form in the 1930s when scientists condensed water vapour on a metal surface cooled to -110°C. Its high-density state was discovered in the 1980s when ordinary ice was compressed at nearly -200°C.
The research team discovered medium-density space ice in 2023. It was found to have the same density as liquid water and would therefore neither sink nor float in water.
Co-author Professor Angelos Michaelides, from the University of Cambridge, concluded: “Water is the foundation of life, but we still do not fully understand it. Amorphous ices may hold the key to explaining some of water’s many anomalies.”