Image: Vladimir Venediktov/Getty Images
A strange new phase of ice has been discovered during experiments with the world's largest X-ray laser. Meet ice XXI, a bizarre phase that forms at room temperature, under extreme pressure.
The solidified water we're most familiar with here on Earth is technically known as ice I, but it's just the tip of the iceberg – for instance, aliens on Neptune could be dropping ice XVIII in their drinks. Exposing plain old H2O to different temperature and pressure conditions could result in more than 20 different phases of the stuff, in fact.
Ice XXI is the latest to join the ranks. It has a tetragonal crystal structure with fairly large repeating units consisting of 152 water molecules, which makes it distinct from all other known phases of ice.
The researchers used a diamond anvil cell at the European XFEL facility in Germany to squeeze water to pressures of up to 2 gigapascals within 10 milliseconds. They then released the pressure relatively slowly – over a leisurely period of one second – before repeating the process. The whole time, the X-rays captured a million images per second to see how the crystal structure changes.
Ice XXI, it turns out, is one of several possible intermediary stages on water's way to becoming an exotic phase known as ice VI. The researchers say the discovery of ice XXI suggests that other, still-unknown phases of ice could exist on icy moon and planets.
Source: Nature