Everyone knows water. But what researchers have now discovered sounds like science fiction. Under extreme conditions, water transforms into a state in which it conducts electricity very well. An international team led by the Helmholtz-Zentrum Dresden-Rossendorf, the University of Rostock and researchers from France has now demonstrated the exact structure of this exotic form of water for the first time. The findings could explain what is going on in the interior of distant planets.
Superionic water only forms where it becomes extreme. Several thousand degrees Celsius of heat and a pressure that is millions of times higher than on the Earth's surface transform normal water into something special. The hydrogen atoms dissolve and migrate freely through a solid lattice of oxygen atoms.
This so-called phase conducts electricity particularly well. The researchers therefore suspect a connection with the unusual magnetic fields of ice giants such as Uranus and Neptune. As these planets contain large amounts of water in their interiors, superionic water could even be the most common form of water in our solar system.
More complex than expected
Until now, it was unclear exactly how the atoms in superionic water are arranged. Earlier studies suggested two possible cube lattice structures. However, the new study shows a much more complex picture. The oxygen atoms form a mixed structure that combines both cube-shaped and hexagonal patterns. Instead of sorting neatly, there are clear errors in the layering. A pattern that can only be made visible through high-precision measurements using state-of-the-art X-ray lasers.
The scientists used two of the most powerful facilities in the world for their experiments. At the European XFEL and at the Linac Coherent Light Source in the USA, they compressed water at a pressure one and a half million times greater than our air pressure and heated it to several thousand degrees Celsius. At the same time, they recorded the atomic structure within a trillionth of a second.
New insights into ice giants
The results show that superionic water has a similar structural diversity to solid ice. Depending on pressure and temperature, it forms different crystal structures. Despite its apparent simplicity, water always reveals new properties under extreme conditions.
The findings provide valuable information for models about the interior and evolution of ice giants. Neptune and Uranus are just two examples. Such planets are also very common outside our solar system.
