Water ice is a far more complex substance than we might assume. Scientists have now created an exotic new form of ice in the lab, known as “plastic ice VII.” This strange version could exist naturally on other planets and moons in our solar system.
The ice in your drinks – and pretty much everywhere else on the surface of Earth – is technically referred to as ice I, but the scientific census actually goes all the way up to ice XIX. These strange types of ice have different crystalline structures and properties, and form under a variety of pressure and temperature conditions.
Contrary to what you might expect, plastic ice VII isn’t the seventh form of plastic ice. Instead, it’s a plastic version of ice VII, a type that’s often created in the lab and has been found deep beneath Earth’s surface. As opposed to ice I’s hexagonal crystalline structure, ice VII has a cubic structure.
Plastic ice VII has the same cubic structure as regular ice VII, but as the name suggests it’s a little more flexible. While the molecules are still locked in a rigid cubic lattice, they can rotate on the spot. This gives the substance a kind of hybrid state between a solid and a liquid.
In the lab experiments, plastic ice VII formed at temperatures of between 127 and 327 °C (260 and 620 °F), and pressures of between 0.1 and 6 gigapascals (GPa).
The discovery was made using a tool called Quasi-Elastic Neutron Scattering (QENS), followed by detailed analysis and simulations of the molecular dynamics. Next, the team conducted neutron and X-ray diffraction measurements to study how ice VII becomes plastic ice VII. Under some circumstances, the transition seems to be continuous.
“The continuous transition scenario is very intriguing as it hints that the plastic phase could be the precursor of the elusive superionic phase – another hybrid exotic phase of water predicted at even higher temperatures and pressures, where hydrogen can diffuse freely through the oxygen crystalline structure,” said Livia Eleonora Bove, corresponding author of the study.
Plastic and superionic phases of ice could exist on planets like Uranus and Neptune, or Jupiter’s moon Ganymede. Understanding this weird substance better could help us work out the dynamics of these worlds.
The research was published in the journal Nature.
Source: Institut Laue-Langevin
