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Time-integrated image of a laser-driven shock compression experiment to recreate planetary interior conditions and study the properties of superionic water. Photo: M. Millot/E. Kowaluk/J.Wickboldt/LLNL/LLE/NIF

Incredibly pressurized and heated on far-off alien worlds, water starts doing things that we can barely conceive of back here on Earth.

A new series of high-tech experiments shows water can be superionized when it is heated to several thousand degrees while under incredibly high pressure – demonstrating that it becomes a hybrid state of matter, as scientists now report in the journal Nature Physics.

This state was originally predicted to exist far-off in the cosmos, on planets like Uranus and Neptune, 30 years ago. Now, after four years of experimentation – with each trial lasting mere nanoseconds – they have validated the concept, report the scientists.

This new water has liquid-like hydrogen ions moving within a solid lattice of oxygen, according to the team from the Lawrence Livermore National Laboratory, the University of Rochester, and the University of California, Berkeley.

“Our work provides experimental evidence for superionic ice and shows that these predictions were not due to artifacts in the simulations, but actually captured the extraordinary behavior or water at those conditions,” said Marius Millot, lead author, a physicist at Lawrence Livermore. “This provides important validation of pf state-of-the-art quantum simulations using density-functional-theory-based molecular dynamics (DFT-MD).”

First, they compressed the water ice, and then they heated it, to find out its melting point properties. This was done so that the scientists could reach the extraplanetary conditions easier in the laboratory.

“Because we pre-compressed the water, there is less shock-heating than if we shock-compressed ambient liquid water, allowing us to access much colder states at high pressure than in previous shock compression studies, so that we could reach the predicted stability domain of superionic ice,” said Millot, in a Lawrence Livermore statement on the work.

The team applied 2.5 gigapascals, approximately 25,000 atmospheres, of pressure to compress water into what is known as room temperature ice VII, which is cubic instead of normal hexagonal ice – and is also some 60 percent denser.

The team then took the ice to the University of Rochester’s Laboratory for Laser Energetics. There they trained the Omega-60 laser at the ice and shot a 1 nanosecond pulse of ultraviolet light, which sent a shock through the entire structure that heated and compressed it simultaneously.

The changes were tracked by interferometric ultrafast velocimetry and pyrometry to understand its thermodynamic properties during the 10 to 20 nanoseconds of the experiments, according to the experts. (After the trials, the pressure-release waves decompressed and vaporized everything).

Two years were spent making the measurements, and two years were spent developing the data analysis methods, Millot said.

The thin-dynamo theory of Uranus and Neptune is thus bolstered by the results, they conclude. The planets have a thin layer of fluid and large “mantle” of superionic ice – as had been suspected , based on the unusual magnetic fields surrounding each.

“It is gratifying that our experiments can test – and in fact, support – the thin-dynamo idea that had been proposed for explaining the truly strange magnetic fields of Uranus and Neptune,” said Raymond Jeanloz, co-author of the paper, from UC-Berkeley. “It’s also mind-boggling that frozen water ice is present at thousands of degrees inside these planets, but that’s what the experiments show.”

Next up: understanding how the oxygen lattice in this unusual ice is structured, added Federica Coppari, another Lawrence Livermore physicist who authored the paper.

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