The study used a special method called density functional theory (DFT), which was derived from quantum mechanics and helps investigate how complicated crystals are made.
Scientists studied the structure of superionic ice, which is also called ice XVIII. It’s a type of water that usually is found in Neptune and Uranus. The negative oxygen ions form a grid-like design while the positive hydrogen ions act like electricity in metals. Superionic ice only exists under very hot temperatures and high pressure, and it could be what causes Neptune and Uranus’ magnetic fields to face different directions. To figure this out, researchers used computers with special programmes (called neural networks) and machine learning tools.
Did you know that the kind of ice you get from your fridge isn’t the only type? Scientists identified more than 20 different “phases” of ice. One special type is called superionic ice, or Ice XVIII. This type is interesting because it might make up Neptune and Uranus–two planets that people call “ice giants”.
Water changes its form in a state called the ‘superionic crystalline phase’. Instead of being molecules (H2O), oxygen becomes negative ions (O2-) which make up an organized structure like a lattice. And, positive hydrogen ions (H+) turn into liquid and can freely float around inside of the oxygen lattice.
Maurice de Koning, a professor from the State University of Campinas’s Gleb Wataghin Physics Institute in Brazil, said that it is like having positive ions inside a metal such as copper. These ‘positive ions’ create a framework but the electrons are able to move freely within this structure.
De Koning was part of an article that was published in a scientific journal and featured on the cover of its November 8, 2022 edition. Superionic ice can only form at high temperatures (around 5,000 kelvins or 4,700 degrees Celsius) and immense pressure (340 gigapascals or over 3.3 million times Earth’s normal atmospheric pressure). This type of ice is so extreme that it doesn’t exist on our planet!
Ice XVIII can be found on Neptune and Uranus, as scientific readings show. The huge gravitational pull from these giant planets push this ice very deep into their mantles.
De Koning said that the electricity that the protons transport through the oxygen lattice has something to do with why the axis of a magnetic field does not match up with the axis of rotation in certain planets. They are actually very different from each other.
The space probe Voyager 2 flew past both Uranus and Neptune. When measure, the angle between the magnetic fields of both planets and their axes of rotation were found to be 47 degrees for Neptune and 59 degrees for Uranus.
In 2019, researchers conducted an experiment on Earth and created a teensy amount of ice XVIII. The ice only lasted one billionth of a second before breaking apart. To make the ice, they used laser-powered shock waves to heat and compress liquid water.
Six powerful laser beams were fired one after another in a planned way to press down a thin layer of water held between two diamonds. The shockwaves bouncing back and forth between the two hard diamonds made sure the pressure on the water stayed even, which resulted in the super-fast creation of an ice-like solid state.
We used computers to study the behavior of ice XVIII, which we think might explain what is happening on planets like Neptune and Uranus. This wasn’t a practical experiment but was done by using simulations on the computer instead.
For this study, scientists used a type of technology from quantum mechanics called density functional theory (DFT) to investigate complex crystalline structures. First, they looked at what happens when there are no defects, or flaws in the material. After that, they added some defects to figure out how it changes the structure and what types of deformations appear.
Crystal defects are usually tiny holes, or the entering of ions from other materials in the crystal. But not here! De Koning was talking about nice big ‘dislocations’, which means that the layers of crystals aren’t lining up properly and are wrinkling like a crumpled rug.
“Scientists studied something called a ‘dislocation’ in crystals back in 1934, but it wasn’t until 1956 that they actually saw it happening! Dislocation is like a defect, and it helps to explain several different things. We could say it’s kind of like DNA being to genetics as dislocation is to metalurgy,” explained De Koning.
In superionic ice, the combination of dislocations causes something called shear. This is a type of stretching that people who study minerals and engineers know about. We figured out how much force it would take to make the crystal shatter because of shear.
The researchers wanted to look at a cell made up of 80,000 molecules. They needed to use very hard and advanced computing technologies like artificial intelligence, machine learning and covering a wide range of scientific fields such as quantum mechanics and planetology. According to him, combining all these specialties was the most fascinating part of the research.
Researchers recently found something really amazing about water ices. They published their findings in a scientific paper called “Plastic Deformation of Superionic Water Ices” which was released on the 2nd of November 2022. This study reveals some really cool stuff!
A research study had some help from FAPESP, a organization that gave money to the first author of the study called Filipe Matusalém de Souza and had supervision from De Koning. Alex Antonelli from UNICAMP made a project for it and there was money from FAPESP’s Program for Research, Innovation, and Dissemination Centers (RIDCs) to fund the Center for Computing in Engineering and Sciences (CCES).
