By Tanish Pradhan
For decades scientists have wondered why the ice giants of the outer solar system, Uranus and Neptune, have a lopsided magnetic field. A physicist from the Lawrence Livermore National Laboratory in California, Dr Marius Millot, and his team may just have found the answer while studying the properties of water. The study has proven the existence of a new form of water called ‘superionic’ water. The presence of this material in the mantles of these planets may be the cause of their strange magnetic fields.
Confirming a theory
The theory that, under conditions of high temperature and pressure, water can take a superionic form was first suggested about 30 years ago. Water molecules are made up of two hydrogen atoms which form a V-shape with a single oxygen atom at the apex. The atoms are held together by weak atomic bonds. When heat is applied, the molecules melt the bonds but the high pressure prevents the water from vaporising.
Under high pressure, oxygen atoms in water can form a solid stacked lattice structure while the ionised hydrogen flows through the structure like a liquid. This gives superionic water the property of electric conductivity, unlike regular ice. Similar to how electrons move in metals, hydrogen ions act as conducting particles in this substance. They would, however, carry a positive charge, unlike negatively charged electrons.
Until recently, the concept of superionic ice was purely theoretical. On Monday, however, a paper published in the Journal of Nature Physics described an experiment which has proved the theory. In this experiment, performed by Dr Millot, water was first squeezed between two diamonds at about 360000 psi—25000 times greater than the earth’s atmospheric pressure. The water is thus squeezed into a form of ice known as Ice VII, that is solid at room temperature. The compressed ice was then moved to the University of Rochester where the researchers blasted it with a laser pulse. The shock waves that passed through the ice did not only exert immense pressure but also heated it to a temperature of several thousand degrees, replicating the conditions that exist within the giant ice planets Uranus and Neptune.
Previous experiments
While previous experiments had produced conductive water, they could not prove that it was ions conducting the charge rather than electrons. Dr Millot’s team, however, managed to capture an optical image of the ice. It was observed that its surface was not shiny, like that of a metal. Instead, it was opaque, indicating that electricity was being conducted through the substance via ionic movement.
In the 1980s when the Voyager 2 spacecraft briefly studied Uranus and Neptune, it discovered that they had unusual magnetic fields. The main theory explaining this holds that the fields are generated not by a metallic core but by shells of superionic ice. The discovery of Dr Millot’s research team supports this theory. Another scientist, Dr Roberto Car who works on computer-simulating superionic ice, has also suggested that different types of superionic ice may exist, varying depending on the lattice structure of the oxygen atoms and on the amount of pressure applied.
Dr Raymond Jeanloz claims that the degree to which the experimental findings conform to the predictions offers the promise that scientists are now genuinely beginning to understand the basic physics of how molecules behave under changing temperatures and pressures. The success of this experiment means that we may have a future in which the rare materials we require could be created by simply feeding the desired properties into a computer.
Featured Image Source: Flickr
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