Strange things happen inside planets where ordinary materials are subjected to extreme pressure and heat. Iron atoms probably dance in Earth’s solid inner core, and hot, black, heavy ice that is simultaneously solid and liquid probably forms on the water-rich gas giants Uranus and Neptune. Five years ago, scientists recreated this exotic ice, called superionic ice, for the first time in laboratory experiments; and four years ago they confirmed its existence and crystal structure.

Then last year, researchers from several universities in the United States and the Stanford Linear Accelerator Center (SLAC) in California discovered a new phase of superionic ice. Their discovery deepens our understanding of why Uranus and Neptune have such irregular multipolar magnetic fields.

From our earthly environment, you would be forgiven for thinking that water is a simple elbow-shaped molecule consisting of an oxygen atom bonded to two hydrogen atoms that occupy a fixed position when the water freezes. Superionic ice is strangely different and yet may be one of the most common forms of water in the universe; It is believed to populate not only Uranus and Neptune, but also similar outer planets.

These planets have extreme pressures of up to 2 million times that of Earth’s atmosphere, and their interiors are as hot as the surface of the Sun; This is where water gets weird.

In 2019, scientists confirmed what physicists predicted in 1988: oxygen atoms in superionic ice are locked in a rigid cubic lattice, while ionized hydrogen atoms are released, flowing through this lattice like electrons through metals. This gives superionic ice its conductive properties. It also raises the melting point, so frozen water remains solid at bubble-forming temperatures.

In this latest study, Stanford University physicist Arianna Gleason and her colleagues bombarded thin strips of water sandwiched between two layers of diamond with incredibly powerful lasers. Successive shock waves increased the pressure to 200 GPa (2 million atmospheres) and the temperature to approximately 5,000 K (8,500 °F); This is higher than the temperatures in the 2019 experiments, but at a lower pressure.

“Recent discoveries of water-rich exoplanets such as Neptune require a more detailed understanding of the phase diagram [води] “At pressures and temperatures consistent with the interior of the planet,” Gleason and colleagues explain in their January 2022 paper.

X-ray diffraction then revealed the crystal structure of hot, dense ice, although pressure and temperature were maintained for only a fraction of a second.

The resulting diffraction patterns confirmed that the ice crystals were in fact a new phase, different from the superionic ice observed in 2019. The newly discovered superionic ice, Ice XIX, has a body-centered cubic structure and increased conductivity compared to its 2019 predecessor, Ice XVIII. .

Conduction is important here because moving charged particles create magnetic fields. This is the basis of dynamo theory, which explains how turbulent conductive fluids inside the Earth’s mantle or another celestial body create magnetic fields. If a large portion of the interior of a Neptune-like ice giant was occupied by a soft solid and a smaller portion by a rotating liquid, this would change the type of magnetic field produced.

And if this planet has two superionic layers at its center with different conductivities, as Gleason and his colleagues suggest Neptune might contain, then the magnetic field created by the outer liquid layer would interact with each differently, making things even weirder.

Gleason and colleagues concluded that the increased conductivity of a superionic ice sheet similar to Ice XIX would contribute to the formation of pulsating multipolar magnetic fields similar to those emanating from Uranus and Neptune.

If so, that would be a satisfying conclusion more than 30 years after NASA’s Voyager II space probe, launched in 1977, passed by two ice giants in our solar system and measured their highly unusual magnetic fields. Source