A planet within a planet… What’s in Earth’s inner core?

In his classic 1864 novel Journey to the Center of the Earth, Jules Verne tells the story of two adventurers who descended through a volcano in Iceland to discover a vast world inhabited by prehistoric creatures and explore the planet’s inner structure. But the true center of the Earth has nothing to do with this fantasy, and is rather more interesting.

Scientists said on Tuesday that an extensive study of the depths of the planet, based on the movement of seismic waves arising from large earthquakes, confirmed the existence of a distinct and well-defined structure within the inner core of the planet. This discovered structure is a raging solid ball of iron and nickel with a diameter of 1,350 km.

The Earth’s diameter is about 12,750 km. The internal structure consists of four layers: a rocky crust from the outside, then a rocky mantle, followed by an outer core of lava, and then the solid inner core. This metallic inner core, approximately 2,440 kilometers in diameter, was discovered in the 1930s, also based on seismic waves traveling through the Earth.

Scientists assumed in 2002 that a deep section separated from the rest is hidden inside this inner core, which is similar to a Russian Matryoshka doll. It was possible, after the progress of earthquake monitoring methods, to confirm this assumption.

Earthquakes release waves that travel across the planet and can reveal features of its internal structure based on the changing shape of these waves. So far, scientists have determined that these waves can bounce up to two times, from one end of the Earth to the other and back. The new study focused on 200 earthquake waves of magnitude greater than six that bounced like ping-pong balls up to five times across the planet.

“We may know more about the surface of other distant celestial bodies than we do about the deep inner structure of our planet,” said Tan-Soon Pham of the Australian National University in Canberra, lead author of the study published in the journal Nature Communications.

“We analyzed digital records of ground motions, known as seismograms, after massive earthquakes in the last decade. Our study was made possible by the unprecedented expansion of seismic networks around the world, particularly the dense networks in the United States, the Alaskan Peninsula and in the European Alps,” Pham added.

The outer shell and the newly discovered spherical body in the inner core are hot enough to melt together, but they are a mixture of iron and nickel, and the reason for this is that the enormous pressure on the center of the Earth makes the core in a solid state.

“I like to think of the inner core as a planet within a planet,” said Hrvoje Tcalcic, a geophysicist at the Australian National University and a co-author of the study. “Of course, it’s a solid ball, about the size of Pluto and a little smaller than the moon.”

Tkalcic added, “If we can somehow dismantle the earth by removing its mantle and the liquid outer core, the inner core will look as bright as a star. Its temperature is estimated at 5,500 degrees Celsius to six thousand degrees Celsius, which is similar to the temperature of the surface of the sun.”

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Pham said that the transition from the outer part of the Earth’s interior to the innermost sphere would appear to be a gradual transition rather than a transition between clear boundaries. The researchers were able to differentiate between the two regions due to the different behavior of seismic waves between them.

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