So Alexander Rosu-Finsen, a postdoctoral scientist in Dr. Salzmann’s research group and the lead author of the Science paper, started smashing up ice. The water ice was first chilled in liquid nitrogen to minus 320 degrees Fahrenheit and then placed in a container along with steel balls. A machine then shook the ice and steel balls, still chilled at ultracold temperatures, back and forth at 20 times per second, pulverizing the ice into tiny bits, a process known as ball milling.

Think of it as a high-tech cocktail shaker.

Dr. Rosu-Finsen then opened the container.

“Lo and behold, something completely unexpected happened,” said Dr. Rosu-Finsen, who is now an associate editor at the journal Nature Reviews Chemistry.

The white material inside looked like what one would expect smashed-up ice to look like, but it had been transformed.

The material was now denser, and much of the crystalline structure had been destroyed, producing an amorphous material. The density, however, did not match the already known high- and low-density amorphous ices. Intriguingly, it fell in between; indeed, it was almost exactly the same density as liquid water. Until now, all of the solid forms of ice, crystalline or amorphous, were either significantly denser or less dense than liquid water.

The researchers named it medium-density amorphous ice, or MDA.

The banging of the steel balls applied a shearing force on the ice crystals, enough to knock the water molecules out of their crystal positions, allowing them to be packed more tightly.

“It’s really cool,” said Marius Millot, a physicist at Lawrence Livermore National Laboratory in California who led the experiment that created superionic water. “What it tells us is that there’s still a lot of things that we don’t understand.”