Plastic ice could theoretically form in oceans of alien planets - but does it actually exist?

Imaginations run wild whenever we think about the properties of alien worlds. Could there be harsh ecosystems, green skies, predatory plants, or gruesome creatures that have never walked planet Earth? In the realm of science fiction, the possibilities are endless.

Outside of franchise films, TV shows and comic books, one strange phenomenon that could exist on alien planets has been predicted for years but scientists could not prove it exists.

Known as plastic ice VII, it’s an uncanny phase of water scientists believe could form in the oceans of worlds deep in space—and it's just been proven to exist and observed for the first time.

What is plastic ice VII?

Plastic ice VII requires extremely high temperatures and pressures to form. When temperatures and pressures rise, water molecules are compelled to adopt various configurations and dynamics.

It has properties of both liquid water and solid ice, hence the name. Physicist Livia Bove, told Science News it is “something intermediate between a liquid and a crystal, you can imagine that it is softer when you squeeze it”.

How did scientists observe plastic ice VII?

A team of researchers from around the world created plastic ice VII by heating water to temperatures as high as 327°C (620 °F) and by increasing its pressure up to six gigapascal. The scientists used advanced instruments at the Institut Laue-Langevin (ILL) in France to closely observe the phase transition of the water.

Plastic ice VII has a unique interwoven cubic structure where the hydrogen atoms are somewhat disordered. However, it's unclear what happens to this structure when it "melts," with some theories suggesting the molecules stay in place while the hydrogen atoms move around.

To understand this phase of water, scientists needed to track the movement of the hydrogen atoms, not just its shape. This is why proving the existence of this phase has been so challenging until now.

The IN5 spectrometer based at Institut Laue-Langevin was used by researchersInstitut Laue-Langevin

One method used to identify ice VII is quasi-elastic neutron scattering (QENS), which tracks tiny particle movements inside substances using neutrons.

Plastic Ice VII was first predicted over 15 years ago as a phase of water that could exist under high pressure and temperature. The research team were able to view hydrogens moving about at the microscopic level when Ice VII is heated up and put under pressure.

However, this was not the end of the story. The molecules viewed inside plastic Ice VII were turning in a staggered way rather than spinning freely. It is believed this may be down to the way hydrogen bonds were broken and restored between the molecules.

The icy worlds in our Solar System, such as Neptune (an ice giant) or Jupiter’s moon Europa (which has a thick icy shell), might have had plastic ice VII in the past, according to the experts. One possible thread for future research is gaining a better understanding of what happened in the past on these planets and moons.

The research was published in Nature.

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