Water has many unique properties. The most striking: unlike other substances, solid water – i.e. ice – is less dense than liquid and therefore floats up on the water. Ice, on the other hand, exists in numerous different forms, all of which have not yet been fully researched. A team led by Christoph Salzmann from University College London is now adding another type of ice to these, as described in "Science": medium-density amoprhous ice (MDA) in contrast to amorphous ice with high or low density.
»We know 20 crystalline shapes of ice, but only two main types of amorphemal ice have been discovered so far: amorphous ice cream with high and low density. In between there is a huge poetry, and the common opinion was that there is no ice within these sealing migration, «says Salzmann. For its experiment, the Working Group Crystallines had put steel balls cooled to minus 200 degrees Celsius in a kind of shaking machine that not only dismantled the ice with the original hexagonal crystal structure, but even shaped.
Instead of the expected white powder in the usual form, the process produced the MDA, which had the same density as liquid water. So it could be water that behaves like a glass, which continues to behave like a liquid even at extremely low temperatures. Over short periods of time it appears solid like a glass, but over very long scales it flows like a highly viscous liquid.
The density difference between the previously known amorphous ice bodies has caused scientists to assume that water actually exists as two liquids at very cold temperatures: at a certain temperature, both liquids could exist side by side, one species float - similar to a mixture of oil and water. This hypothesis was demonstrated in a computer simulation, but was not confirmed by experiments. Your new study now raises questions whether this hypothesis is sustainable at all, the researchers said.
On Earth, amorphous ice is extremely rare or, of course, does not exist at all. But there could well be MDA on the icy moons of Saturn and Jupiter, Salzmann and Co. speculate. The tidal forces of the two gas giants can exert similar shear forces on ordinary ice as the steel balls in the experiment. If MDA is heated and allowed to crystallize again, it also releases a lot of thermal energy. Transferred to an ice moon like Ganymede, tectonic movements and "ice tremors" might be triggered in its kilometer-thick ice layers, which could be detected by satellites.
