The inner core is the most inaccessible place on our planet, with extreme conditions: its temperature can even exceed that of the surface of the Sun. It is a solid ball of iron and nickel that rotates, just like the other layers of the Earth, and is of a question: has this rotation stopped? The answer is no.
second one article recently published in the journal “Nature Geoscience” and led by Xiaodong Song and Yi Yang of Peking University, it has slowed down and is slightly “offset” from the rotational speed of the rest of the planet. Although in this study the scientists speak of a “recent arrest” and that the rotation of the nucleus may have “reversed”, this does not mean that it has suddenly stopped or is in the opposite direction from the Earth’s surface.
There are nuances, and one of them is that these are relative speeds (in relation to another object) and a trend reversal, said Maurizio Mattesini, a professor of Earth Physics at the Complutense University of Madrid and a researcher at the Institute of Geosciences Agency EFE (IGEO) of the National Research Council of Spain (CSIC).
According to him, “analyzing the inner core is important for understanding the dynamics of the planet and its state of health.”
What is the inner core?
The Earth is made up of several layers, and in the center, at a depth of 5,000 kilometers, is a sphere almost entirely made of iron. It is the inner core, with a radius of 1,220 kilometers – slightly larger than Pluto – and is surrounded by a 2,260 kilometer thick layer of similar composition, but in a molten state, a kind of “mattress”.
The inner core was discovered in 1936 by the Danish seismologist Inge Lehmann when she analyzed seismic waves.
Convection movements in the liquid outer core, together with the Earth’s rotation, generate the magnetic field, which protects the Earth from highly energetic particles from the Sun and space, explain Alberto Molina, Marina Puente and Pablo Rivera, also from IGEO.
Surrounding the core is the mantle, about 2,900 kilometers thick, and above it is the Earth’s crust.
How is the inner core studied?
Analyzing the deepest layer of the Earth is difficult. With drilling to collect samples it is impossible, said Mattesini, who points out that the deepest hole ever drilled is less than 12 kilometers deep.
Computed tomography still has technological limitations, so the alternative is seismology.
Earthquakes generate seismic waves that propagate through the planet’s interior, and some travel through the inner core, from where they emerge at the Earth’s surface. It is then that seismographs record a signal containing information from the center of the Earth.
The planet rotates and it takes about 24 hours to make one full rotation. Until now it was thought that the inner core continued in the same dynamics recorded in the last decade, i.e. rotating a little faster than the mantle and crust, which is called “superrotation”, whereby it advanced by about a tenth of a degree every year.
The first research that talks about superrotation dates back to 1996 – Song was also involved – although subsequent studies have stated the opposite (there is even a minority who argue that there are no distinctions in the rotation). There is sufficient data, but the differences are so subtle that they are open to interpretation and scientific discussion.
What does the latest Nature Geoscience study conclude? The core, since 2009, would have slowed down to the same speed of rotation as the outer layers or even to a slightly lower speed.
These differences in relative speeds are very small, the IGEO scientists explain in their paper.
For example, a car traveling at 120 kilometers per hour is overtaken by a car traveling at 121 kilometers per hour. “From the window we will see that it is slowly passing us. If the other vehicle slows down and reaches 120 kilometers per hour, we will see it ‘stationary’ next to our car, even if it is still moving, like us. “
Similarly, the core would have slowed down and now, rotating at the same speed as the mantle and crust of the earth’s surface, we would see it as stationary.
Thanks to the geological record, as IGEO explained on Twitter, we know that years in the geological past lasted more days, i.e. the Earth rotated faster and therefore the days were shorter (in the Mesozoic they lasted 23 hours).
This is because the Moon is moving away from us at a speed of 3.82 centimeters per year, and its effect is a slowdown in rotation, imperceptible on a human scale.
The new study found that the speed at which the Moon was braking was experiencing outliers. Using seismic wave propagation from earthquakes, it was discovered that this could be due to differential rotation of the core.
It’s not the first time
This slight change in core rotation isn’t the first time: data show another similar event in 1970.
This suggests that the phenomenon repeats itself with a periodicity of about 2 or 3 decades, or even 7, depending on the authors, and it seems that this same frequency appears in other observable geophysical phenomena, such as the geomagnetic field, the length of the day – a millisecond plus or minus, depending on rotation – or time, which suggests they might be related.
But this is only a hypothesis, Mattesini warned, noting that there is still no scientific evidence.
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Of course, the actual time it takes Earth to complete one rotation varies slightly, which is important for fine-tuning navigation systems, and the days are getting longer again.
To find out what is behind this and the complex dynamics of the Earth, we must continue to investigate.
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