The discovery of a strange form of ice that only melts at very hot temperatures

Strange things happen inside planets, where familiar materials are subjected to extreme pressures and heat.

Iron atoms are likely dancing within Earth’s solid inner core, and hot, heavy, black ice – which is both solid and liquid – is likely forming inside the water-rich gas giants Uranus and Neptune.

Five years ago, scientists recreated this strange ice, called superionic ice, for the first time in laboratory experiments; Four years ago, they confirmed its existence and crystal structure.

Then just last year, researchers at several US universities and the Stanford Linear Accelerator Center Laboratory in California (SLAC) discovered a new phase of super-ionized ice.

Their discovery deepens our understanding of why such things exist on Uranus and Neptune Magnetic fields outside the kilter range With multiple electrodes.

From our terrestrial surroundings, you would be forgiven for thinking that water is a simple elbow-shaped molecule consisting of a single oxygen atom bonded to two hydrogen atoms that snap into a fixed position when the water freezes.

Super ice Oddly different, yet it may be among The most abundant forms of water in the universe – presumably filling not only the interiors of Uranus and Neptune, but also similar outer planets.

These planets have extreme pressures two million times Earth’s atmospheric pressure, and their interiors are as hot as the surface of the Sun, which is where water becomes alien.

In 2019, scientists confirmed what physicists had confirmed Expected in 1988: A structure in which the oxygen atoms in superionized ice are trapped in a solid cubic lattice, while the ionized hydrogen atoms are released, flowing through that lattice like electrons through metals.

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This gives superionic ice its conductive properties. It is too It raises its melting point So that frozen water remains solid at high temperatures.

In this latest study, physicist Arianna Gleason of Stanford University and her colleagues bombarded thin strips of water, sandwiched between two layers of diamond, with some ridiculously powerful lasers.

Successive shock waves raised pressures to 200 gigapascals (2 million atmospheres) and temperatures of about 5,000 K (8,500 degrees Fahrenheit) — hotter than the temperatures of the 2019 experiments, but at lower pressures.

“Recent discoveries of water-rich, Neptune-like exoplanets require a more detailed understanding of the planet’s phase diagram. [water] “At the pressure and temperature conditions relevant to their planetary interiors,” Gleason and colleagues said explained in their paperfrom January 2022.

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

The resulting diffraction patterns confirmed that the ice crystals were actually a new phase different from the superionized ice observed in 2019. The newly discovered superionized ice, Ice Body-centered cubic structure And increased conductivity compared to its predecessor from 2019, Ice XVIII.

Conductivity is important here because moving charged particles generate magnetic fields. This is the basis Dynamo theorywhich describes how conductive fluids, such as the Earth’s mantle or inside another celestial body, give rise to magnetic fields.

If more of the interior of a Neptune-like ice giant was sucked in by a soft solid, and less by a rotating liquid, it would Change the type of magnetic field produced.

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If this planet contains two superionized layers with different conductivity towards its core, as Gleason and his colleagues said Suggest Neptune might have, and then the magnetic field generated by the outer liquid layer would interact with each of them differently, making things even stranger.

Neptune’s internal structure is made up of two layers of superionized solid ice (ice 19 in blue, ice 18 in green) beneath an ionic liquid layer that is thought to generate the planet’s magnetic field. (Gleeson et al., Scientific reports2023)

Gleason and colleagues We conclude The enhanced conductivity of a layer of superionized ice similar to Ice XIX would promote the generation of unstable, multipolar magnetic fields like those emitted by Uranus and Neptune.

If so, it would be a satisfying result more than 30 years after NASA’s Voyager 2 space probe, launched in 1977, flew by Earth. Our solar system has two Ice giants And measurement they Very unusual magnetic fields.

The study was published in Scientific reports.

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