Earth’s inner core is a strange mixture of superionic fluids

(ORDO NEWS) — The Earth’s inner core may be composed of liquid light elements rotating among a solid lattice of iron, according to computer simulations.

A team of physicists recently modeled how alloys of iron and lighter elements such as hydrogen, carbon and oxygen would behave at extremely high temperatures and pressures at the center of our planet.

Under these conditions, the iron part of the mixture remained solid, but the lighter elements turned into the so-called superionic liquid: a state more fluid than a solid, but not quite as fluid as a liquid.

According to an article by physicist Yu He of the Chinese Academy of Sciences and colleagues, published in February in the journal Nature, this combination of solid iron and superionic hydrogen, carbon or oxygen could explain several highly puzzling things that seismologists have observed in the interior of our planet.

WHAT’S NEW – Simulations carried out by him and his colleagues suggest that in the conditions of the inner core, a simple alloy of iron and carbon can turn into something with a much more complex structure. And this, in turn, may explain some of the most puzzling things that seismologists have observed in the inner depths of our planet.

In computer models based on quantum mechanics, He and his colleagues simulated what would happen to molten mixtures of iron and various combinations of hydrogen, carbon and oxygen at a temperature of about 5200 degrees Celsius and a pressure of about 3.6 million atmospheres. This is exactly what the inner core of the Earth is like, which begins about 5,300 kilometers below our feet.

It turned out that under such conditions iron becomes solid; its atoms stay in one place, quietly vibrating. But atoms of lighter elements, such as those that He and his colleagues think are most likely part of a mixture of molten material in the Earth’s core, oscillate more, flowing almost – but not quite – like a liquid. As a result, a strong framework of iron atoms is formed, and a liquid mixture of lighter atoms floats between them.

When He and his colleagues modeled the movement of seismic waves through a model of the Earth’s inner core, the results were very similar to real seismic data. This suggested to the researchers that their model is a plausible explanation for what is going on in our planet’s core. It also suggested that superionic fluids in the Earth’s core could explain why seismic waves move through the inner core the way they do.

HERE IS THE STORY – During an earthquake, some seismic waves, called surface waves, propagate through the earth’s crust, while others, called body waves, go right through the planet’s inner core.

Measuring how quickly body waves travel through the planet’s layers and how their properties change along the way can reveal information about our planet’s structure. For example, thanks to body waves, we know that the core of the Earth has two layers, and the outer layer consists mainly of liquid iron.

Measuring seismic waves passing through the Earth’s core has also allowed scientists to know that it is made of something slightly less dense than pure iron.

Light elements such as hydrogen, carbon and oxygen are likely to be part of the mixture, forming a combination called an alloy. These elements are likely suspect because they are three of the four most common elements in our solar system, and they have been part of the Earth’s interior since the formation of the planet.

However, seismologists have noticed that certain seismic waves passing through the Earth’s inner core slow down much more than they should if they pass through a solid ball of evenly mixed iron alloy. This means that something else must be going on in the inner core.

“Seismological observations show that the structure of the inner core is complex and difficult to understand,” He and colleagues write in their paper, but they say their recent modeling may point to the answer to what they call “the long-standing seismic mystery of the inner core.” “.

WHY IT’S IMPORTANT – He and his colleagues say their model could explain why seismic waves slow down as they pass through the Earth’s inner core, and also why seismic waves travel through the center of the Earth about 3 percent faster pole-to-pole than they do through the equator.

Pressure waves such as sound and seismic waves travel faster through denser materials. Superionic liquids are less dense than solids; their atoms are further apart and move more freely. This means that seismic waves will not travel as fast through a superionic liquid as they do through a solid body, which could explain why seismic waves slow down on their way through the Earth’s inner core.

Meanwhile, if the iron atoms in the inner core are solid and motionless, then the superionic light elements are in constant motion.

The Earth’s inner core is hotter, but some areas are hotter than others. This creates a constant movement called convection as hot material tends to rise and colder material sinks. Convection in the Earth’s mantle causes the tectonic plates to move, causing earthquakes whose seismic waves help us understand the core.

If He and his colleagues are right, convection in the inner core will keep the superionic fluid moving among the solid lattice of iron atoms. This constant flow may mean that some parts of the inner core may contain more solid pieces than others, or more liquid. And that could explain why seismic waves move a little faster from pole to pole.

“This phenomenon may provide an alternative interpretation of the different travel times of such earthquakes,” write He and his colleagues.

A better understanding of how superionic fluids work in the Earth’s core could help us understand other worlds as well. Some planetary scientists also suggest that superionic fluids may exist in the interiors of ice giants such as Neptune, Uranus, and similarly sized exoplanets.

What’s next – the Earth has a magnetic field, because the liquid iron of the outer core also moves due to convection, and this movement creates a giant electromagnet in the center of our planet. He and his colleagues suggest that the Earth’s magnetic field may also influence how superionic carbon, hydrogen and oxygen move around in the inner core.

On the other hand, deep inside the ice giants Neptune and Uranus, convecting superionic fluids may indeed influence the planets’ magnetic fields.

Whether there is a connection between magnetic fields and superionic fluids in the Earth’s inner core will require further research, but the findings may tell us something new about the dynamo that powers our planet.

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