Rare Ice That Could Form on Alien Worlds Observed

For the first time, scientists have observed plastic Ice VII, a form of water previously predicted by theoretical models. While it might sound like the title of a B-movie, this is actually an exotic phase of water that experts believe could form in the oceans of alien planets.

The Unique Structure of Plastic Ice VII

So, what makes this ice so unusual? Plastic Ice VII forms only under extreme temperature and pressure conditions. As these factors increase, water molecules are forced into a variety of unique configurations and behaviors.

An international team of researchers successfully created Ice VII by applying a pressure of 6 gigapascals and heating water to 327°C (620°F) at the Institut Laue-Langevin (ILL) in France. They closely monitored the phase change using advanced instruments.

Plastic Ice VII exhibits a distinctive interwoven cubic structure where hydrogen atoms become disordered. However, scientists have never fully understood how this structure behaves when it “melts.” Some theories suggested that the molecules remain fixed while the hydrogens move around.

To explore this exotic phase, precise measurements were necessary to track the hydrogen movement rather than just capture its shape. This challenge had prevented scientists from proving its existence—until now.

One of the key techniques used to detect Ice VII was quasi-elastic neutron scattering (QENS), a method that traces tiny particle movements by utilizing neutrons. “QENS’ ability to probe both the translational and rotational dynamics gives it a unique advantage for exploring these phase transitions compared to other spectroscopic methods,” said physicist Maria Rescigno from Sapienza University of Rome.

Unexpected Behavior of Ice VII Molecules

As predicted 17 years ago, the team observed hydrogen atoms rotating at the microscopic level when Ice VII was subjected to heat and pressure. However, they were surprised to find that the molecules did not rotate freely but instead moved in staggered steps. This likely occurs due to the breaking and reforming of hydrogen bonds between molecules.

“The QENS measurements suggested a different molecular rotation mechanism for plastic Ice VII than the free rotor behavior we initially expected,” Rescigno explained.

Experts believe icy worlds in the outer reaches of the Universe, such as Neptune or Jupiter’s moon Europa, might have hosted plastic Ice VII in the past. Understanding its behavior in the lab provides insights into the history of these distant planets and their moons.

One area for further research could be investigating how plastic Ice VII forms—whether the transition is gradual or abrupt, as suggested by some models.

Plastic Ice VII as a Precursor to the Superionic Phase

“The continuous transition scenario is particularly intriguing,” said physicist Livia Bove from Sapienza University. It could mean that plastic Ice VII is a precursor to the superionic phase—a rare form of water that is predicted to exist at even higher temperatures and pressures, where hydrogen freely diffuses through the oxygen crystalline structure.

Read the original article on: Science Alert

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