A strange type of ice thought to dwell deep in the oceans of alien planets has finally been proven to exist.
For the first time, researchers have directly observed a sort of hybrid phase of water called plastic ice, which forms at high temperatures and pressures and exhibits traits of both solid ice and liquid water. The observations, reported February 12 in Nature, may help researchers better understand the internal architecture and processes of other worlds in our solar system and beyond, some of which might be habitable.
Plastic ice is “something intermediate between a liquid and a crystal, you can imagine that it is softer when you squeeze it,” says physicist Livia Bove of Sapienza University of Rome. It’s called plastic ice because it is more easily molded or deformed than typical crystalline ice, exhibiting a property scientists call plasticity, she says. “Like something that can [squeeze] through a hole and come out, even if it’s still solid.”
Most of the ice on Earth’s surface — including ice cubes, glaciers and snow — consists of water molecules arranged in a hexagonal lattice that resembles a honeycomb. Scientists classify this common ice as ice lh. But in addition to ice Ih, there are at least 20 other known ice phases that form in different pressure and temperature conditions. At pressures above 20,000 bars — or 20,000 kilograms per square centimeter — ice lattices compress into Ice VII, a polymorph with a dense, cubic structure in which molecules are ordered like the cubies in a Rubik’s Cube. Ice VII has been found trapped in diamonds originating from Earth’s mantle and is thought to occur inside other planets too. And Kurt Vonnegut fans may be interested to hear that an ice IX was discovered in 1996, though it lacks the terrifying ability to freeze entire oceans.
There are also ice phases that have only been theorized to exist. Over 15 years ago, computer simulations showed that…
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