A strange form of ice that's found naturally only on alien worlds has been captured being frozen from water in real time on Earth for the first time, U.S. researchers said Tuesday.
In a study published online in the U.S. journal Physical Review Letters, researchers at the Stanford University described how ice VII, or ice seven, which normally forms in environments such as when icy planetary bodies collide, was created and imaged in the lab in just billionths of a second.
"These experiments with water are the first of their kind, allowing us to witness a fundamental disorder-to-order transition in one of the most abundant molecules in the universe," said study lead author Arianna Gleason, a postdoctoral fellow at Los Alamos National Laboratory and a visiting scientist in the Extreme Environments Laboratory of Stanford's School of Earth, Energy & Environmental Sciences.
Under regular conditions on our planet's surface, water crystallizes in only one way, dubbed ice Ih or simply "hexagonal ice," whether in glaciers or ice cube trays in the freezer.
To create ice VII, Stanford researchers used the Linac Coherent Light Source, the world's most powerful X-ray laser.
First, the science team beamed an intense, green-colored laser at a small target containing a sample of liquid water.
The laser instantly vaporized layers of diamond on one side of the target, generating a rocket-like force that compressed the water to pressures exceeding 50,000 times that of Earth's atmosphere at sea level.
As the water compacted, a second beam from an instrument called the X-ray Free Electron Laser arrived in a series of bright pulses, each of which lasts only a femtosecond, or a quadrillionth of a second.
Akin to camera flashes, this X-ray laser snapped a set of images on the progression of molecular changes as the pressurized water crystallized into ice VII.
The phase change took just six billionths of a second, or nanoseconds, and during this process, the water molecules bonded into rod shapes, and not spheres as theory predicted, the team said.
Delving into extraterrestrial ice types, including ice VII, will help scientists model such remote environments as comet impacts, the internal structures of potentially life-supporting, water-filled moons like Jupiter's Europa, and the dynamics of jumbo, rocky, oceanic exoplanets called super-Earths.
"Any icy satellite or planetary interior is intimately connected to the object's surface," Gleason said. "Learning about these icy interiors will help us understand how the worlds in our solar system formed and how at least one of them, so far as we know, came to have all the necessary characteristics for life."
