It has taken one of the most powerful lasers on the planet, but scientists have done it. They have confirmed the existence of "superionic" hot ice: frozen water that can remain solid at thousands of degrees of heat.
This strange form of ice is possible due to tremendous pressure, and the findings of the experiment could shed light on the inner structure of giant ice planets such as Uranus and Neptune.
On the surface of the Earth, the boiling and freezing points of water vary only a little; They usually boil when it is very hot and when it is cold. But both changes of state are produced by the whim of the pressure (that's why the boiling point of water is lower at higher altitudes).
In the vacuum of space, water can not exist in its liquid form. It immediately boils and vaporizes even at -270 degrees Celsius, the average temperature of the Universe, before being de-ablated in ice crystals.
But it has been theorized that in extremely high pressure environments, the opposite occurs: the water solidifies, even at extremely high temperatures. Scientists at Lawrence Livermore National Laboratory observed this for the first time recently, detailed in an article last year.
They created Ice VII, which is the crystalline form of ice above 30,000 times the atmospheric pressure of the Earth, or 3 gigapascals, and bombarded it with lasers. The resulting ice had a conductive flow of ions, instead of electrons, which is why it is called superionic ice.
Now they have confirmed it with follow-up experiments. They have proposed that the new form be called Ice XVIII.
In the previous experiment, the team had only been able to observe general properties, such as energy and temperature; the finer details of the internal structure remained elusive. So they designed an experiment using laser pulses and X-ray diffraction to reveal the crystal structure of ice.
"We wanted to determine the atomic structure of the superionic water," said physicist Federica Coppari of the LLNL.
"But given the extreme conditions in which it is predicted that this difficult state of matter will be stable, compressing water at such pressures and temperatures and at the same time taking snapshots of the atomic structure was an extremely difficult task, which required an experimental design innovative".
Here is that design. First, a thin layer of water is placed between two diamond anvils. Then, six giant lasers are used to generate a series of shock waves at a progressively increasing intensity to compress water at pressures of up to 100-400 gigapascals, or 1 to 4 million times the atmospheric pressure of the Earth.
At the same time, they produce temperatures between 1,650 and 2,760 degrees Celsius (the surface of the Sun is 5,505 degrees Celsius).
This experiment was designed so that water would freeze when compressed, but since pressure and temperature conditions could only be maintained for a fraction of a second, physicists were not sure that ice crystals formed and grew.
So they used lasers to shoot a small piece of iron foil with 16 additional pulses, creating a plasma wave that generated an X-ray flash at the precise moment. These flashes difractaron of the crystals in the interior, showing that the compressed water was congealed and stable.
"The X-ray diffraction patterns we measure are an unambiguous signature of the dense ice crystals that form during the ultra-fast compression of the shock wave, which shows that the nucleation of solid ice in liquid water is fast enough. to be observed in the time scale of the experiment in nanoseconds, "said Coppari.
These x-rays showed a structure never before seen: cubic crystals with oxygen atoms in each corner and an oxygen atom in the center of each face.
"Finding direct evidence of the existence of a crystal lattice of oxygen brings the last missing piece to the puzzle regarding the existence of superionic water ice," said physicist Marius Millot of the LLNL.
"This gives additional strength to the evidence of the existence of superionic ice that we collected last year."
The result reveals a clue to how ice giants such as Neptune and Uranus could have such strange magnetic fields, tilted at odd angles, and with ecuadores that do not surround the planet.
Previously, it was thought that these planets had a fluid ocean of ionic water and ammonia instead of a mantle.
But the team's research shows that these planets could have a solid mantle, like Earth, but made of hot superionic ice instead of hot rock. Because the superionic ice is highly conductive, this could be influencing the magnetic fields of the planets.
"Because the water ice in the interior conditions of Uranus and Neptune has a crystal lattice, we argue that the superionic ice should not flow as a liquid as the Earth's outer iron core, rather, it is probably better to imagine that the superionic ice would flow similarly "to Earth's mantle, which is made of solid rock, flows and supports large-scale convective movements on very long geologic time scales," Millot said.
"This can dramatically affect our understanding of the internal structure and evolution of the frozen giant planets, as well as all of their numerous extrasolar cousins."
The research has been published in. Nature.