GoKawiilIce comes in more forms than what you’ll find in a freezer or a glacier. Since 1900, scientists have observed more than 20 phases of ice, many of them shaped under extreme conditions. The growing list includes hot ice and even ice that conducts electricity.
Ice is the name for any phase of water that is solid and crystalline, meaning that it has a repeating molecular structure. Over the past decade, computer simulations have predicted tens of thousands of possible forms of ice. Though uncommon on our planet, exotic ice may exist in off-Earth environments, from cold and amorphous comet tails to the hot and crushing cores of icy planets.
As physicists put water to the test with improved experimental techniques, they keep finding surprises. “You take water, and just the way you compress it — a little bit faster, a bit slower, up and down, at the right timescale — and then you can find this completely unexpected behavior,” said Marius Millot, a research scientist at Lawrence Livermore National Laboratory (LLNL) in California.
Abandoning old assumptions and applying new techniques, scientists have discovered three new kinds of ice in the past year, including two of the most complex ice phases ever seen. “It seems a remarkable time at the moment,” said Chris Pickard, a physicist at the University of Cambridge. “They’re really finding a lot more of these structures.”
Space Oddity
The shape of water makes it exceptionally versatile. Its molecular structure can assemble in many possible configurations.
Each water molecule looks like a central unit with four arms spread apart by the electromagnetic force. The central unit is an oxygen atom. Bonded to it are two hydrogen atoms, and sticking out like extra limbs are two pairs of leftover free electrons.
Mark Belan/Quanta Magazine
In the most common form of ice, these building blocks combine to form a cagelike hexagonal structure. The spaciousness of this arrangement makes typical ice less dense than liquid water. This is why ice floats, and why bodies of water freeze from the top down, allowing underwater life to survive the winter.
Put water under pressure, though, and its shape can compress and overlap in a seemingly endless bounty of possible patterns. Because it can take so many different forms, “the physics and the chemistry of water can be completely different” from one environment to the next, said Livia Bove, a physicist at the Swiss Federal Institute of Technology Lausanne. “It’s topologically beautiful.”
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