Weird water phase “ice-VII” can grow as fast as 1,000 miles per hour

Enlarge / Artistic representation of a shock wave experiment on water, used to form exotic ice-VII in the lab, against background of hypothetical ocean world. (credit: Lawrence Livermore National Laboratory)
Kurt Vonnegut's 1963 novel Cat's Cradle introduced the world to so-called 'Ice Nine,' a fictional form of water that freezes at room temperature. If it so much as touches a drop of regular water, that will freeze, too, and so on, spreading so rapidly that it freezes everything that comes into contact with it.
Fortunately for Earth, Ice-Nine doesn't exist. But there is an exotic form of ice dubbed 'ice VII' that physicists can create in the laboratory. It's harmless in terrestrial conditions. But on an ocean world like Jupiter's moon, Europa, it could behave just like Ice-Nine under the right conditions, freezing an entire world within hours—with some key implications for the possibility of finding life on distant exoplanets. Now we know more about just how that special freezing process occurs, according to a recent paper in Physical Review Letters.
It's the shape formed by the water molecules that determine which phase of ice you get. That ice in your glass of whiskey is technically ice Ih—'h' for hexagon, since that's the shape that all the oxygen atoms line up in during freezing. But in theory, there should be at least 17 different crystalline phases of water—which one you get depends on the pressure and temperature of any given environment.
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