Earth’s Inner Core Rotation Appears to Be Slowing Down

Earth’s solid metal core may no longer be spinning relative to the vast mass of the surrounding planet thanks to what appears to be a recent slowdown, according to the results of a new study.

Nestled at the heart of our planet is a vast, 2,400 km-wide ball of solid metal, which is surrounded by an outer core made up of super-heated liquid iron and other materials.

This liquid barrier acts to separate the solid inner core from the vast mass of the surrounding Earth, allowing it to spin independently. Scientists have long believed that the central core spins significantly faster than the outer mantle and crust of our planet. 

This phenomenon, known as super-rotation, is thought to be partially responsible for the generation of Earth’s protective magnetic field, and may even have an impact on the temperature of the oceans and the length of each day.

However, according to new research published in the journal Nature Geoscience, the core’s speed may have slowed significantly in recent decades.

In the recent study — reported on by Vice — a team of scientists analyzed the data from seismic waves created by powerful earthquakes that passed through our planet’s crust, and interacted with the inner and outer core. These earthquakes occurred mostly between 1995 – 2021 at locations spread around the globe.

Some geologists believe that the spin of the central core affects the amount of time that it takes for seismic waves to travel through the planet, and that, by tracking variations in the speed of waves that occur in close proximity to each other, they are able to gauge the rotational speed of Earth’s core. Earlier studies used this technique to estimate that the enormous metal ball used to spin roughly one tenth of a degree faster than the surrounding mantle each year.

However, according to the results of the new study, Earth’s core may have now stopped spinning relative to the rest of the planet. According to the seismic data, the change may have actually taken place as far back as 2009, and the core may now be poised to shift into a period of ‘subrotation’, wherein it will spin slower than the rest of our world.

“There are two major forces acting on the inner core,” said study authors Yi Yang and Xiaodong Song of Peking University to Motherboard. “One is the electromagnetic force. The Earth’s magnetic field is generated by fluid motion in the outer core. The magnetic field acting on the metallic inner core is expected to drive the inner core to rotate by electromagnetic coupling. 

“The other is gravity force. The mantle and inner core are both highly heterogeneous, so the gravity between their structures tends to drag the inner core to the position of gravitational equilibrium, so called gravitational coupling.”

According to the researchers, imbalances in the two forces can cause the core to accelerate or decelerate. To their surprise, the pair also found that the core also appears to have stopped spinning independently of the mantle back in the early 1970s, which suggests that its rotation may naturally shift in a 70-year recurring cycle.

However, its worth noting that not all scientists agree that the core does spin faster than the rest of the Earth, and instead suggest that aberrations in the travel time of seismic waves could instead result from changes on the surface of the vast metal core.

Yang and Song are now waiting for more earthquakes to send seismic waves through the core in order to further test their theory. NASA is also planning to launch a mission to explore what could be the exposed metal core of a shattered ancient planet, which could shed light on the inner workings of Earth and the other worlds that populate our solar system.

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Anthony is a freelance contributor covering science and video gaming news for IGN. He has over eight years experience of covering breaking developments in multiple scientific fields and absolutely no time for your shenanigans. Follow him on Twitter @BeardConGamer

Image Credit: Vadim Sadovski