When you take an ice cube to the fridge or look out at a cold winter landscape full of ice formations, you’re interacting with the substance we all know as ice, or hexagonal ice (Ice Ih). But what if I told you that there are about twenty different types of ice, and each one is completely different from what you know? One type of ice is so unique that it’s only found deep in the mantles of celestial bodies like Neptune and Uranus. Meet Ice XVIII, also known as superion ice.

Professor Maurice de Kooning has published research describing the complexity of superionic ice and its potential to further understand the strange properties observed in the “ice giants” in our solar system.

The intriguing phenomenon of superionic ice

So what makes superionic ice so special?

Ice XVIII is anything but ordinary. It is produced under extreme conditions; temperatures reach 5,000 Kelvin (about 4,700 degrees Celsius) and pressure is about 340 gigapascals, 3.3 million times greater than atmospheric pressure at the Earth’s surface.

Although Earth does not have such harsh conditions, the ice giants Neptune and Uranus exist deep inside, thanks to their enormous gravitational fields. In superionic ice, water does not retain its typical molecular structure. The oxygen atoms form a rigid lattice, while the hydrogen atoms, stripped of their electrons, float freely as positively charged ions.

“It is similar to a metallic conductor, such as copper, but it has positive ions that form a crystal lattice and negatively charged electrons that move freely,” explains de Koning, Distinguished Professor of the Gleb Vatagin Institute of Physics at the State University of San Campinas. Paulo, Brazil

Why is superionic ice important?

Superionic Ice, or Ice XVIII, fascinates scientists with its unique position. How these free-floating hydrogen ions pass through the oxygen lattice could potentially explain the unusual properties of Uranus and Neptune, especially the peculiar behavior of their magnetic fields.

Unlike Earth, where the magnetic field is aligned with the axis of rotation, Uranus and Neptune have a noticeable tilt in the axes of their magnetic field — 47 and 59 degrees from the axis of rotation, respectively.

This discrepancy has puzzled scientists for a long time. De Koning’s research suggests that the movement of these protons in superionic ice may be the cause. He explains: “The electricity that the protons conduct through the oxygen lattice is closely related to the question of why the magnetic field axis does not coincide with the rotation axis of these planets.”

Deep in the mantles of the “ice giants”

To further investigate this theory, De Koning and his team abandoned traditional experiments and turned to advanced computer simulations.

Using density functional theory (DFT), they modeled the mechanical properties of ice XVIII to understand how it would behave under the intense conditions on Neptune and Uranus. The task was no walk in the park. Simulating ice XVIII required accounting for a large number of molecules (about 80,000).

The calculations used advanced computational methods, neural networks and machine learning algorithms. The main goal was to explore how different types of defects in the crystal structure could be associated with large-scale deformations and thus with mysterious magnetic fields.

Crystal defects and other imperfections

In the crystal world, defects are usually thought of as imperfections that disrupt the normal arrangement of atoms. But these defects in superionic ice may hold the key to its mystery. The study investigated a specific type of defect known as a “dislocation”, which occurs when there is an angular difference between adjacent crystal layers.

De Koning uses a simple analogy: “Imagine a crumpled carpet; the resulting wrinkles are somewhat like dislocations in a crystal.” He goes on to explain: “Dislocations are to metallurgy what DNA is to genetics.”

By modeling these dislocations in Ice XVIII, the team concluded that the force required to deform the ice could explain the planets’ unique magnetic properties. They found that the special conditions on Neptune and Uranus, combined with the properties of Ice XVIII, create an ideal environment for these phenomena.

Superionic ice in the laboratory

Superionic ice may seem like a science fiction concept, but it’s becoming increasingly critical to our understanding of the universe. In 2019, scientists created a small amount of Ice XVIII by using high-powered lasers to squeeze a thin layer of water between diamond surfaces—a feat that opens up vast possibilities for future research.

But for now, our understanding of superionic ice is largely similar to the simulations run by de Kooning. “This was the most interesting aspect of the research, combining insights from metallurgy, planetary science, quantum mechanics and high-performance computing,” he explains.

Working on ice to learn about the universe

Understanding superionic ice could not only satisfy our curiosity about what lies inside distant planets, but could also transform our understanding of the fundamental physics that governs all matter.

As we discover more about states similar to those found on Uranus and Neptune, we may discover new materials or properties that could find applications here on Earth, from superconductors to new types of energy storage.

So the next time you pull an ice cube out of the freezer, take a moment to appreciate the immersive world of Ice XVIII. It’s a reminder of how much we still have to discover in our universe and on Earth.