Water, the elixir of life, can exist in many forms beyond the familiar liquid, solid, and gas. Scientists recently discovered a new phase of ice, Ice-VIIt, formed under extreme pressure. This discovery has significant implications for our understanding of icy celestial bodies and even the size of exoplanets. This unique ice phase doesn’t exist naturally on Earth’s surface, but could be present deep within our planet’s mantle or on distant moons and planets.
Ice-VIIt boasts a tetragonal symmetry, contrasting with the cubic structure of its precursor, Ice-VII, and the hexagonal symmetry of everyday ice (Ice-I). This structural difference means Ice-VIIt crystals resemble rectangular prisms rather than cubes. The research detailing this discovery was published in Physical Review B.
“The prevailing belief within the ice research community was that cubic Ice-VII was the dominant high-pressure phase,” explained Zachary Grande, a physicist at the University of Nevada, Las Vegas and lead author of the study. “However, our innovative technique enabled more accurate measurements, revealing this subtle quantum transition.”
To create Ice-VIIt, researchers subjected water to immense pressure within a diamond anvil cell, effectively squeezing water molecules between two diamonds. A laser briefly melted the sample before allowing it to refreeze into this new configuration. Pressures similar to those at Earth’s core were needed to force Ice-VII to transition into Ice-VIIt.
“Zach’s work shows that this transition to an ionic state happens at far lower pressures than previously imagined,” stated Ashkan Salamat, a physicist at UNLV and co-author of the research. “It’s a missing piece of the puzzle and represents the most precise measurements ever taken on water under these conditions.”
Though Earth’s interior is incredibly hot, high-pressure ices like Ice-VIIt possess correspondingly high melting points. While regular ice melts at 32° Fahrenheit, Ice-VIIt requires a scorching 1,340° F to liquefy. This extreme resilience suggests Ice-VIIt may exist within Earth’s mantle.
Furthermore, Ice-VIIt transitions to Ice-X at significantly lower pressures than previously thought—just one-third of the initially estimated pressure. This Ice-X finding carries substantial implications for our understanding of exoplanets.
“If planets have significant water within their mantles, they could be larger than current estimates suggest, as the water won’t compress as readily,” Grande explained. “This necessitates a re-evaluation of the water content on many large exoplanets discovered recently.”
The James Webb Space Telescope, with its capacity for detailed exoplanet observation, may play a key role in this reassessment.
The discovery of Ice-VIIt opens exciting new avenues for planetary science and our understanding of water’s behavior under extreme conditions. Further research may uncover even more surprising properties of this unique ice phase and its role in the universe.
