Strange new form of ice discovered in high pressure experiments
Ice may seem pretty simple in our everyday experience, but it actually comes in at least 20 different forms. Scientists at the University of Nevada Las Vegas (UNLV) have now discovered a new type of ice that may be found deep in the Earth’s mantle or on distant watery planets.
The ice you’d drop into a drink is officially known as ice I, appropriately enough, but the currently known scientific tally goes all the way up to ice XIX. These different forms manifest as different crystal structures, and appear when ice or water is subjected to different combinations of temperatures and pressures.
In the new study, the UNLV team developed a new technique to measure the properties of water under high pressure. First, water is placed in a diamond anvil cell, where the sample is squeezed between two diamond plates, forcing the oxygen and hydrogen atoms into different arrangements. Then, the ice that formed is zapped with a laser to briefly melt it, before it then refreezes into another form, resembling a powder of tiny crystals.
While experimenting with different pressures, the researchers discovered a completely new type of ice, as a transitional stage between two known forms. At around 5.1 GigaPascals of pressure, the cubic structure known as ice VII transformed into a never-before-seen phase consisting of symmetrical tetragonal crystals. This new phase was named ice VIIt. After that, it then settled into another known phase called ice X.
Given the strong pressure required to produce it, the team says ice VIIt could be common in the Earth’s mantle, as well as that of other planets. It may even appear closer to the surface on water-rich exoplanets.
The new ice wasn’t the only discovery the team made in these experiments. Ice X was previously thought to form at around 1 million atmospheres of pressure, but in the new study it was observed appearing at just 300,000 atmospheres. That drastically changes where it might appear in nature.
The research was published in the journal Physical Review B.