Made new type of ice that could exist on distant moons (icon image)
Photo: Alexander Rosu-Finsen / Christoph Salzmann
As cubes, with raspberries, in the shape of a flamingo: Many people produce ice cubes in their freezer at home.
Researchers have now created a new form of the substance - by shaking it in a container with steel balls.
The ice, which formed at about minus 196 degrees, has very different properties than normal, crystalline water ice, the scientists report in the journal Science.
They had created the special material by shaking ice between small stainless steel balls.
It is possible that the newly produced form of ice can be found on icy moons in the solar system, such as Jupiter's moon Ganymede.
"We know of 20 crystalline forms of ice, but so far only two main types of amorphous ice, known as high-density and low-density amorphous ice, have been discovered," said co-author Christoph Salzmann of University College London.
Crystalline means that the water molecules are arranged in a strict crystal lattice that can take different forms.
Amorphous, on the other hand, is the state in which the molecules are largely disordered, as is the case in liquid water.
The amorphous form occurs when there is not enough energy available for ordering the crystal lattice during freezing.
Astronomers suspect that water ice in space is mostly in an amorphous form.
First in the form »ordinary ice cream with stacking error«
While the one known form of amorphous ice at minus 196 degrees has a density of just 0.94 grams per cubic centimeter, the value for high-density amorphous ice is at least 1.13 grams per cubic centimeter.
At 1.06 grams per cubic centimeter, the newly discovered form achieves a value in between.
That's why the researchers call it medium-density amorphous ice.
For comparison, the density of ordinary water ice just below zero is less than all of these forms, 0.917 grams per cubic centimeter.
It's less dense than liquid water, which is why icebergs float on water.
When heat is applied to the new form of ice, which looks like a fine white powder, it first changes to the form of "stacked-disordered ice," and later to ordinary ice.
This happens at normal ambient pressure of around 100,000 pascals.
When the researchers subjected the ice to pressure of a billion pascals and then heated it, they measured a surprisingly large amount of energy released as heat.
It corresponds to about 70 percent of the energy that is released when water freezes into ordinary ice.
"Tidal forces inside ice moons, which are caused by the gravitational forces of gas giants, can cause shear forces similar to those caused by ball milling," the researchers explain, referring to the manufacturing process of their new ice.
In turn, the extraordinary amount of heat released as the medium-density amorphous ice recrystallizes into ordinary ice may have helped activate tectonic plate movements.
So there could be movements on Jupiter's moon Ganymede that are similar to plate tectonics on Earth.
The key now is to understand how much of the amorphous ice in space has intermediate density and how geophysically active it is, said co-author Angelos Michaelides of University College London.
In addition, the new ice form must be examined more closely.
At 1.06 grams per cubic centimeter, it has a density similar to that of liquid water, which is around 1.0 grams. The researchers therefore speculate that the new ice form could be the glassy state of water - an exact replica of liquid water in solid form, just as glass in windows is the solid form of liquid silicon dioxide.