A weird form of ice could prove to be a massive help in determining which water worlds are capable of harboring life.

Ice VII is an exotic phase of water which can be formed by decompressing the heavy water ice VI below 95 K. In addition to that, it can be created in a number of other ways including rapid compression through shock waves and increasing the pressure on ice VI at ambient temperatures. It has a triple point with liquid water and ice VI at 355 K and 2.216 GPa. Just like the other ice phases, the positions of Hydrogen atoms are distorted in ice VII. Some of the Oxygen atoms also move away from their regular positions. Having said that, it is the only disordered ice phase that can be arranged by simple cooling, which makes it the most stable among all the molecular phases of ice.

Recently, a study published in the journal ‘Physical Review Letters’ suggested that this strange type of ice can grow at over 1,000 miles per hour given the atmospheric conditions on some of the alien ocean worlds. The shape of atoms in an ice crystal is used to classify different phases of ice. The ice all of us use in our daily lives is known as ‘Ih’. The alphabet ‘h’ represents the hexagonal shape of the of the Oxygen atoms in this phase of ice. There are a total of 17 theoretical phases of ice but liquid water can only be converted into 5 of them, directly. That list includes Ih, ice III, ice V, ice VI, and ice VII. The number of the ice represents the increase in pressure that is needed to form that form of ice.

Naturally occurring Ice VII was discovered earlier this year in March. It was trapped inside diamonds that were more 400 miles beneath the surface of the Earth. This was an amazing finding as it provided evidence for the existence of liquid water within Earth’s core. The researchers at the Lawrence Livermore National Laboratory used a mathematical model to determine that there is a certain pressure threshold across which Ice VII can grow rapidly. The name given to this instantaneous process is ‘Nucleation’. Alex Chernov, one of the Physicists who took part in this research, said,

“This is a regime where the limits of our physical understanding are being tested.”

Generally, shock waves are used to compress liquid water at around 100,000 times more pressure than the normal atmospheric pressure. The problem with this method is that the results of different experiments have contradicted with each other as some of them showed homogenous transition while others voted in favor of heterogeneous transition. This was the trouble which forced the scientists to find out the reasons behind these variations. Philip Myint, the Lead Author of the paper, talked about that in the following words:

“The conditions created by shock compression are unusual in that they produce an enormous driving force for the system to nucleate. The liquid is driven away from equilibrium so quickly that it takes additional time for clusters to appear, a process known as transient nucleation.”

The experiments proved by the team of Myint showed that the nucleation of Ice VII is highly dependent on the pressure levels applied to the water and the temperature of the sample. Up to a certain level of pressure, ice VII starts to form at edges and work its way in. As soon as the pressure crosses that threshold, the ice starts forming homogenously throughout the sample. Having said that, it will only happen if the temperature of forming ice crystals is different from the liquid water. Initially, ice VII forms in 100-molecule clusters before spreading viciously to all parts of the sample.

It is an extraordinary discovery as it will help astrobiologists to find life on those exoplanets who are covered in water. Although water is one of the primary factors to determine whether life could exist on a planet or not, the presence of water in form of Ice VII eliminates all the chances of harboring any kind of life. Jonathan Belof, a Material Chemist at the Lawrence Livermore National Laboratory, referred to that by saying,

“Water on these ocean worlds, under bombardment from other planetary bodies such as meteors or comets, undergoes intense changes for which life might not survive. The shock wave launched by the explosions from these planetary impact events can compress water to a pressure over 10,000 times that found on the Earth’s surface and cause the water to freeze into ice VII.”