A new type of ice called medium-density amorphous ice has the same density as liquid water, so studying it could help us understand the strange behavior of water at low temperatures.
Physics
February 2, 2023
The ice was made by colliding very cold steel ball bearings with normal ice. Christoph Salzmann
Researchers have discovered a completely new form of ice. Ice is amorphous, meaning it doesn’t have a well-organized crystalline structure, which could help unlock the mysteries of liquid water.
We already knew there are two types of amorphous ice: high density and low density. There’s a gap in the middle, and researchers thought there was no way to make medium-density amorphous ice, or MDA.but when Christoph Salzmann University College London and his colleagues placed ordinary ice with a hexagonal crystal structure in a tumbler with steel ball bearings cooled to -200°C (-328°F).
“This was one of the experiments we did on Friday afternoon to see what would happen,” says Salzmann. “Simply break the ice into pieces, thinking nothing is going to happen. But to our great surprise, something happened.”
The fine white powder produced in the experiment had a density about the same as that of liquid water, and just halfway between the two other known forms of amorphous ice. This has led the researchers to suggest that it may be water in what is called the glassy phase, a type of substance that continues to behave like a liquid even at extremely low temperatures. On short timescales, glass may appear solid, but on longer timescales it flows like a viscous liquid.
Liquid water may seem mundane, but when it is cooled to extremely low temperatures, it hides a mystery. Based on the gap between low-density amorphous ice and high-density amorphous ice, it is possible that supercooled water actually exists in two different liquid phases at once, one floating on top of the other. Although researchers have previously suggested that there is a
“It’s not a normal ice-like crystal, it’s the surface of ice as you know it, and it has the same density as liquid water. The big question is what this is,” Salzman says. “I believe that if we can figure out what this MDA is, we can better understand liquid water.”
MDA may also be an important component of icy moons in the outer solar system. These strange worlds experience strong shear forces due to the host planet’s gravity, potentially creating the right conditions for MDA to form. The researchers also found that when this ice warms, it releases an extraordinary amount of heat, which could have a very large impact on the geological activity of those worlds.
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