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The inner core of the Earth is in a state somewhere between liquid and solid.

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Physicists have long held that Earth’s inner core is solid, but a new study suggests it lies somewhere in between solid and liquid, a discovery that could shed light on some of the planet’s deepest secrets.

An investigation led by the Institute of Geochemistry of the Chinese Academy of Sciences (IGCAS), has concluded that the inner core of the Earth does not have a completely solid conformation, as was thought until today. On the contrary, it is in an intermediate state between liquid and solid, which is also known as superionic state. Apparently, this fact could explain the changes that have been recorded in the inner core during the last decades.

The inner core of the Earth is the deepest geological layer of the planet. It is a sphere with a radius of approximately 1,220 kilometers, which constitutes about 20% of the radius of the Earth. It is not possible to make direct measurements of the inner core in the absence of samples, but the analysis of seismic waves and the Earth’s magnetic field have allowed scientists to know some of its characteristics.

The temperature on the surface of inner core it is located at around 5,430 degrees Celsius, that is, approximately the temperature that the surface of the Sun would have. According to current theories, the inner core is composed of a solid iron-nickel alloy, with some other elements. However, according to a press release, the new investigation could cast doubt on its formation.

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The inner core is superionic

Using molecular dynamics simulations, the researchers confirmed that the hydrogen, oxygen and carbon that are integrated into compact iron in the Earth’s inner core transform to a superionic state, under the conditions that exist in the deep heart of our planet. Although they present a intermediate state between liquid and solidthese elements behave in part like a liquid, diffusing and expanding rapidly.

The discovery suggests that the entire inner core may be in a superionic state, rather than a normal solid state. It was already known that the inner core is less dense than pure iron and that some light elements make up its structure, but it had not been possible to determine that this constitution modified the general state of the core. In addition, the liquid-type light elements lead to a substantial reduction in the seismic velocitieswhich are close to the latest seismological observations of the inner core area.

The new study, recently published in the journal Nature, concludes that the dynamics of light elements have a potential influence on the seismological structure and, furthermore, on the very Earth’s magnetic field. Although it is believed that the magnetic field appears to be generated primarily by fluid and electrical currents in the outer core, these currents are strongly affected by the inner core and the intense heat that flows from it.

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mysteries to solve

At the same time, the results clearly indicate that the liquid elements are what make the inner core softens, a fact that emerges from seismological observations. In addition, the impact on seismic velocities provides new clues to understand other mysteries in the inner core of the Earth.

For example, seismic wave attenuations and structural changes of the inner core during the last decades can be understood in terms of the superionic model, by considering the distribution and convection of liquid elements in the inner core.

As the superionic state is common inside other planetary bodies, its presence in the inner core of the Earth could also shed light on aspects that exceed our planet, such as how the inner planets of the Solar System developed. It could also serve as a parameter to discover aspects of the conformation of extrasolar planets or exoplanets, some of which show characteristics similar to Earth.

Reference

Superionic iron alloys and their seismic velocities in Earth’s inner core. Yu He, Shichuan Sun, Duck Young Kim, Bo Gyu Jang, Heping Li, and Ho-kwang Mao. Nature (2022). DOI:https://doi.org/10.1038/s41586-021-04361-x

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