A form of ice that can normally only form in the depths of space has been filmed being frozen from water on Earth, one molecule at a time.

Ice VII is usually only found when icy planets or comets collide in space. This type of ice is created in a very fast phase transition. This process has now been recreated in the lab while being filmed as it happened for the first time. The results are published in Physical Review Letters.

"There have been a tremendous number of studies on ice because everyone wants to understand its behavior," said study author Wendy Mao Stanford University in a statement. "What our new study demonstrates, and which hasn't been done before, is the ability to see the ice structure form in real time."

Measuring this process in real time was no mean feat. It required the world's most powerful X-ray laser, the Linac Coherent Light Source at the SLAC National Accelerator Laboratory in the US.

First, the team shot a very intense green laser at a target containing a sample of water. This vapourised diamond held on one side of the target, to create pressures 50,000 times greater than atmospheric pressure at sea level.

Hartley 2
The icy comet Hartley 2 pictured by NASA's EPOXI mission. The rare Ice VII forms when icy bodies collide in space. NASA/JPL-Caltech/UMD

This put huge pressure on the water and compacted it. While this was going on, a second laser beam zapped the water from the X-ray Free Electron Laser for several incredibly short blasts – each lasting less than a quadrillionth of a second. This was used to create a series of images on incredibly short time scales, measuring the changes going on in the water sample.

The images successfully revealed Ice VII forming. However, they also showed that this structure didn't form with molecules forming spherical shapes but rather rod shapes, overturning the conventional theory of how Ice VII forms.

Understanding this formation will improve our understanding of the watery, rocky planets that could potentially support life beyond Earth, the authors say.

"Any icy satellite or planetary interior is intimately connected to the object's surface," said Arianna Gleason of Los Alamos National Laboratory and a visiting scientist at Stanford University, and also a study author.

"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."