Research

Water of unusual shape may be the most common in the universe.

Recently in the Laboratory of laser energy inBrighton, New York, one of the most powerful lasers in the world hit a drop of water, creating a shock wave that raised the pressure in this water to millions of atmospheres, and the temperature to thousands of degrees. X-rays that went through this drop in the same split second showed the first glimpse of water to humanity in such extreme conditions. They showed that the water inside the shock wave did not become superheated liquid or gas. No, the water is frozen.

Paradoxically, the atoms of water froze to form crystalline ice. However, as the physicists assumed, squinting at the screens in the next room.

"You hear the shot and at the same moment you see thatsomething interesting happened, ”says Marius Millo of the Livermore National Laboratory. Lawrence, who conducted the experiment with Federica Coppari.

What happens to water at high pressure and temperature?

The results of this paper, published on thisA week in Nature confirms the existence of "superionic ice," a new phase of water with fancy properties. Unlike ice familiar to you, which can be found in the freezer or at the north pole, superionic ice is black and hot. The cube of such ice weighed four times more than usual. For the first time its existence was predicted more than 30 years ago, and although it has never been seen before, scientists believe that it can be one of the most common types of water in the universe.

Even in the solar system, most of the water,probably in the form of superionic ice - in the depths of Uranus and Neptune. Its more than liquid water in the oceans of Earth, Europe and Enceladus. The discovery of superionic ice could solve old riddles about the composition of these “ice giants”.

Scientists have already discovered eighteen amazingice crystal architectures, including the hexagonal arrangement of water molecules in ordinary ice (Ih). After ice-I, which is of two forms, Ih and Ic, the other forms are numbered from II to XVII in the order of opening. Yes, “ice-9” actually exists, but its properties are not at all the same as in Kurt Vonnegut’s novel Cat's Cradle.

Superionic ice can claim mantleIce XVIII. This is a new crystal, but there is one thing in it. All previously known water ices consist of intact water molecules, in which one oxygen atom is bound to two hydrogen atoms. But superion ice, as new measurements show, is not like that. It exists in a kind of surrealistic limb, half solid, half liquid. Separate water molecules disintegrate. Oxygen atoms form a cubic lattice, but hydrogen atoms flow freely, flowing like a liquid through a rigid oxygen cell.

Specialists say the detection of the superionicIce justifies computer predictions that can help material scientists create future substances with individual properties. And the detection of this ice required ultra-fast measurements and precise temperature and pressure control, which became possible only with improved experimental methods.

"It was all impossible to do, say, fiveyears ago, ”says Christoph Salzmann of University College London, who opened the ice-XIII, -XIV and XV. "It will certainly have a huge impact."

Physicist Libya Bove of the National Center for ScientificFrench studies believe that since water molecules disintegrate, this is not an entirely new phase of water. "This is a new state of matter, which is quite impressive."

Puzzles on ice

Physicists have been hunting for superionic ice for many years -since the primitive computer simulation of Pierfranco Demontis in 1988 predicted that water would take on this strange, almost metallic form if it was pushed out of the map of the known ice phases.

The simulation showed that under strong pressureand the heat of the water molecule is destroyed. Oxygen atoms are enclosed in a cubic lattice, and “hydrogen starts jumping from one position in the crystal to another, again and again,” says Millo. These jumps between lattice sites are so fast that hydrogen atoms — which are ionized, turning, in fact, into positively charged protons — behave like a liquid.

It has been suggested that superion icewill conduct electricity like a metal, and hydrogen will play the role of electrons. The presence of these free hydrogen atoms will also enhance the disorder of ice, its entropy. In turn, an increase in entropy will make ice more stable than other types of ice crystals, with the result that its melting point will rise.

It's all easy to imagine, believe it -difficult. The first models used simplified physics, crawling through the quantum nature of real molecules. Later simulations added more quantum effects, but still bypassed the actual equations needed to describe the interaction of several quantum bodies, which is too difficult to calculate. Instead, they relied on approximations, which increased the likelihood that the whole scenario would turn out to be a mirage in the simulation. The experiments, meanwhile, could not create the necessary pressure and generate enough heat to melt this strong substance.

And when everyone has already abandoned this venture, planetologistsexpressed their own suspicions that water may have a superionic phase of ice. At about the same time that this phase was first predicted, the Voyager-2 probe went into the outer solar system and discovered something strange in the magnetic fields of the ice giants Uranus and Neptune.

The fields around the other planets of the solar system,apparently consist of strictly defined north and south poles, with no particular other structure. It seems as though they contain bar magnets aligned with the axes of rotation. Planetologists associate this with a “dynamo”: internal regions where conductive fluids rise and rotate as the planet rotates, creating enormous magnetic fields.

In contrast, magnetic fields emanating from Uranus andNeptune, looked more bulky and complex, with more than two poles. They also did not align closely with the rotation of their planets. One way to achieve this is to somehow limit the conductive fluid responsible for the dynamo to the thin outer shell of the planet, instead of allowing it to penetrate into the core.

But the idea that these planets may havesolid cores unable to generate dynamos did not seem realistic. If you had drilled these ice giants, you would expect to first encounter a layer of ionic water that will flow, conduct currents and participate in a dynamo. It seems that even deeper material, even at higher temperatures, will also be liquid, but this is naive. Planetary scientists have a joke that the bowels of Uranus and Neptune cannot be firm at all. But it turned out that they can.

Explosive ice

Coppari, Millo and their team put the puzzle pieces together.

In an earlier experiment published inIn February 2018, physicists obtained indirect evidence of the existence of superionic ice. They squeezed a drop of water at room temperature between the pointed ends of two cut diamonds. When the pressure rose to about gigapascal, which is about 10 times more than at the bottom of the Mariana Trench, the water turned into a tetragonal crystal, ice-VI. At 2 gigapascals, it turned into ice-VII, a denser, cubic form, transparent to the naked eye, which scientists have recently discovered also exists in tiny pockets inside natural diamonds.

Then, using the OMEGA laser in the lablaser energy, Millo and his colleagues set their sights on ice-VII, still sandwiched between diamond anvils. When the laser hit the surface of the diamond, it vaporized the material up, essentially throwing the diamond in the opposite direction and sending a shock wave through the ice. Millo's team found that super-crushed ice melted at a temperature of about 4,700 degrees Celsius, as expected for super-ionic ice, and that it conducted electricity through the motion of charged protons.

After making predictions regarding bulkSuperionic ice properties were confirmed, a new study by Coppari and Millo was supposed to confirm its structure. If you want to confirm the crystalline nature, you need X-ray diffraction.

Their new experiment missed ice-VI and ice-VIIat all. Instead, the team simply broke the water between the diamond anvils with laser shots. After billions of fractions of a second, while the shock waves penetrated through and the water began to crystallize into nanometer-sized ice cubes, scientists added another 16 laser beams to evaporate a thin piece of iron next to the sample. The resulting plasma flooded the crystallizing water with X-rays, which then diffracted from the ice crystals and allowed the team to discern their structure.

The atoms in the water were reorganized into the long-predicted, but never-before-seen architecture, ice-XVIII: a cubic lattice with oxygen atoms at every corner and center of each face.

"This is a real breakthrough," says Koppari.

“The fact that the existence of this phase is not an artifact of quantum molecular dynamic simulation, but quite real is very pleasing,” says Bove.

And this kind of successful cross validation likemodeling, and the present superionic ice suggests that the ultimate "dream" of researchers in material physics can soon be achieved. “You tell me what kind of material properties you need, we go to the computer and theoretically find out what material and crystalline structure you need,” says Raymond Janloz, a scientist at the University of California at Berkeley.

The new analysis also hints that althoughSuperionic ice does conduct some electricity, it is a loose, but solid substance. It will gradually spread, but not flow. Thus, the liquid layers inside Uranus and Neptune can stop approximately 8000 kilometers inland, where the huge mantle of unstable superionic ice will begin. This limits most dynamo actions at shallower depths, given the unusual fields of the planets.

Other planets and moons of the solar system,probably, they do not have internal temperatures and pressures that would allow superionic ice to exist. But the multitude of exoplanets the size of ice giants suggest that this substance - superionic ice - will be distributed in ice worlds throughout the galaxy.

Of course, no planet will contain oneonly water. Ice giants in our solar system are also mixed with methane and ammonia. The extent to which superionic behavior actually finds a place in nature “will depend on whether these phases exist when we mix water with other materials,” scientists say. However, superionic ammonia must also exist.

Experiments are ongoing. Do you think we will once know what is in the center of the largest bodies in our solar system? Share your opinion in our chat in Telegram.