Concept of an icy exoplanet. Image: © bogdan/Stock.adobe.com
Researchers from UCD and Canada have observed protons ‘hopping’ in a high-pressure type of ice.
A new discovery could tell us more about the ice that exists on distant planets. In a paper published to Science Advances, researchers from University College Dublin (UCD) and the University of Saskatchewan in Canada described the first observation of ‘proton hopping’ in lattices of a high-pressure form of ice referred to as ‘ice VII’.
Such movement may be present on planets such as Venus, Jupiter, Neptune, Uranus and distant exoplanets, mediated by external electric fields. The discovery of this electric conduction in ice has the potential to change our understanding of the behaviour and molecular dynamics of high-pressure ice in the universe.
Unlike common water ice (ice I), ice VII is a cubic crystalline form of ice which can be formed from liquid water at pressures above 3 gigapascals (GPa), or nearly 30,000 atmospheres. This is achieved when liquid water’s temperature is lowered to room temperature, or by decompressing heavy-water ice VI below 95 kelvin.
Molecular ‘musical chairs’
Given ice VII’s simple structure and stability, it has been put forward as a potential candidate for a super-ionic (SI) ice phase. Within ice VII, it’s believed oxygen atoms remain crystallographically ordered while protons become fully diffusive as a result of intramolecular dissociation.
SI ice studies have suggested its presence in large-planet mantles, such as Uranus and Neptune, as well as exoplanets and planets with transient electric fields such as Venus.
Speaking of the breakthrough, Prof Niall English of UCD said this discovery, where protons skip from one water molecule to the next and displace the proton on the next chain, is “akin to musical chairs”, thereby establishing an electric current or a flow of charge.
“This has important implications for hypothesised ice VII in various planetary and exoplanetary bodies, featuring permanent or transient electric fields, such as the environs of Venus and moons of Jupiter such as water-rich Europa, and, especially, Ganymede,” he said.
For astronomers, English added, it has the potential to lead to possible spectroscopic detection of exotic phases of ice in the universe.
