In a recent incident, one of the world’s most powerful lasers at the Laboratory for Laser Energetics in Brighton, New York, blasted a droplet of water, creating a shock wave that elevated the water’s pressure to millions of atmospheres and its temperature to thousands of degrees. X-rays that streamed through the droplet in the same fraction of a second presented our first glimpse of water under those extreme conditions.
The x-rays exposed that the water inside the shock wave didn’t convert to a superheated liquid or gas. Paradoxically and just as the physicists who were glued to their screens in an adjacent room had expected, the water atoms froze solid, forming crystalline ice.
Marius Millot of Lawrence Livermore National Laboratory in California who co-led the experiment with co-worker Federica Coppari, said, “You hear the shot, right away you see that something interesting was happening.”
Their findings, published in Nature, report the existence of “superionic ice,” a new phase of water with bizarre properties. In contrast to the familiar ice found in our freezer or at the north pole, superionic ice is hot and black. A cube of this ice would weigh four times more than the normal one. Its existence was first theoretically predicted over 30 years ago, and even though it has never been seen directly until now, scientists believe it might be among the most abundant forms of water in the universe.
Across the solar system, in any case, more water probably exists as superionic ice occupying the interiors of Uranus and Neptune than in any other phase, counting the liquid form abundant in oceans on Earth, Europa, and Enceladus. This discovery of superionic ice possibly solves decades-old puzzles about the composition of these “ice giant” worlds.
Scientists had previously discovered a bewildering 18 architectures of ice crystal Including the hexagonal arrangement of water molecules found in common ice, known as “ice Ih,”. After ice I, which comes in two forms, Ih and Ic, the rest are numbered II through XVII in order of their discovery. ice IX also exists but only under contrived conditions.
Superionic ice has now claimed the mantle of ice XVIII. It’s a new crystal but with a difference. All the formerly known water ices are composed of intact water molecules, each with one oxygen atom linked to two hydrogen atoms. But the new measurements confirm that superionic ice isn’t like that. It exists in a kind of surrealist limbo, part solid, part liquid where individual water molecules break apart, oxygen atoms form a cubic lattice while the hydrogen atoms spill out, free to flow like a liquid through the rigid enclosure of oxygens.