Thursday, May 19, 2022

A new form of ice discovered

Findings could have implications for our understanding of distant, water-rich planets.

There are at least 20 solid forms of ice known to us. Recently, UNLV scientists have discovered a new form of ice, redefining the properties of water at high pressures.

Scientists devised a new method to measure the properties of water under high pressure. They started with squeezing a water sample between the tips of two opposite-facing diamonds—freezing into several jumbled ice crystals. The ice was then exposed to the laser-heating technique that melted it temporarily. It then quickly reformed into a powder-like collection of tiny crystals.

By gradually raising the pressure and intermittently obliterating it with a laser beam, the group saw that the water ice moved from a known cubic stage, Ice-VII, to the newfound intermediate and tetragonal stage, Ice-VIIt, before settling into one more known stage, Ice-X.

This transition to Ice-X occurs at much lower pressures than previously thought.

Zach Grande, a UNLV Ph.D. student, said, “While it’s unlikely we’ll find this new phase of ice anywhere on the surface of Earth, it is likely a common ingredient within the mantle of Earth as well as in large moons and water-rich planets outside of our solar system.”

Scientists are continually working to understand the behavior of high-pressure water that may be present in the interior of distant planets.

To do so, scientists placed a water sample between the tips of diamond anvil cells. They then applied a small force to the diamonds. This allowed scientists to recreate pressures as high as those found at the center of the Earth.

Squeezing water samples allowed scientists to drive the oxygen and hydrogen atoms into various arrangements, including the newly discovered arrangement, Ice-VIIt.

Doing so, scientists observed a new phase of water ice. At the same time, they found that the transition to Ice-X occurred at pressures nearly three times lower than previously thought—at 300,000 atmospheres instead of 1 million. This transition has been a highly debated topic for several decades.

Grande and UNLV physicist Ashkan Salamat said“Zach’s work has demonstrated that this transformation to an ionic state occurs at much, much lower pressures than ever. It’s the missing piece and the most precise measurements on the water at these conditions.”

“The work also recalibrates our understanding of the composition of exoplanets. The Ice-VIIt phase of ice could exist in abundance in the crust and upper mantle of expected water-rich planets outside of our solar system, meaning they could have conditions habitable for life.”

Journal Reference:

  1. Zachary M. Grande et al., Pressure-driven symmetry transitions in dense H2O ice, Physical Review B (2022). DOI: 10.1103/PhysRevB.105.104109

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