© Shutterstock

Recent study -

In early February 2025, researchers published a study in the journal Nature that suggests the shape of the Earth’s mysterious inner core may be changing.

© Shutterstock

Previous research -

Already in 2023, scientists discovered that around 15 years prior to that point the rotation of the Earth’s inner core slowed down so much that it may have paused, or even reversed.

© Shutterstock

Expanding knowledge -

The most recent study builds on that research, suggesting that when it comes to the Earth’s inner core, it is not only its rotational direction that can change, but its very shape, too.

© Shutterstock

No direct observations -

Of course, given the extreme conditions present at the center of the Earth, it is not possible to observe and monitor these changes directly.

© Shutterstock

How the observations are made -

Scientists therefore use earthquake waves to make assumptions about what is happening in the Earth’s inner core.

© Shutterstock

Our planet's various layers -

Of all the Earth’s layers, the inner core is the one that scientists know least about. Indeed, it is the most remote and therefore the hardest to observe.

© Shutterstock

Solid sphere of metal -

What we do know is that the Earth’s inner core is a solid sphere of metal and that it has a radius of around 759 miles (1,221 kilometers).

© Shutterstock

Temperatures -

Temperatures in the inner core can reach up to 9,800°F (5,400°C), and pressure can be as high as 365 gigapascals (GPa).

© Shutterstock

Perspective -

For perspective, that’s around three million times greater than the Earth’s average atmospheric pressure on land.

© Shutterstock

Changing state -

For a long time, scientists believed that the inner core existed in a permanent state. In light of emerging research, however, that belief is starting to change.

© Shutterstock

Looking at seismic waves -

As previously mentioned, researchers use the seismic waves created by earthquakes in order to study the Earth’s inner core.

© Shutterstock

The South Sandwich Islands -

Typically, they use waves from earthquakes that occur in the South Sandwich Islands near Antarctica and travel through the planet to Alaska.

© Shutterstock

From Antarctica to Alaska -

The waves travel through the Earth like sonar waves through water, and some of them pass through the Earth’s core on their journey to Alaska.

© Shutterstock

Detecting changes -

In order to reliably detect changes to the Earth’s inner core, scientists compare similar-sized earthquakes that occur in the same place but at different times.

© Shutterstock

Doublets -

If the journeys of these twin quakes—known as doublets—are identical, they should generate the same waveforms.

© Shutterstock

Important observation -

However, while looking at decades of data, scientists have observed that some doublets in the South Sandwich Islands generate different waveforms in Alaska.

© Shutterstock

Interpreting the results -

This suggests that something about the Earth’s inner core has changed during the period before the first and second quakes of the doublet.

© Shutterstock

Rotational change -

The first change that geophysicists reported was related to the direction of the Earth’s inner core rotation.

© Shutterstock

Long since understood -

For some time now, scientists have been aware that the inner core of Earth spins independently to, and faster than, the rest of the planet.

© Shutterstock

Revelations of 2023 -

However, in 2023, scientists reported that the spinning of the inner core had slowed so much that it appeared to either completely stop, or even reverse.

© Shutterstock

Revisiting the data - Then, in 2024, a closer look at the data led researchers to confirm the suspected reversal.

© Shutterstock

Some 200 pairs of quakes -

For the study published in February 2025, researchers looked at data from roughly 200 pairs of earthquakes that occurred between 1991 and 2024.

© Shutterstock

Subtle differences observed -

They observed subtle differences in 10 doublets and concluded that the simplest explanation would be a deformation to the shallow inner core.

© Shutterstock

How the changes may happen -

In terms of how the inner core may be changing, there are two main possibilities. The first is that the entirety of the inner core is being deformed.

© Shutterstock

Useful metaphor -

Imagine a football being reshaped so that its two ends are now pointing in two new directions.

© Shutterstock

Small patches -

The other possibility is that small patches of the Earth’s inner core may be swelling and contracting. If this is the case, the metaphorical football would have the same overall shape, but it would also have various small dents and bumps.

© Shutterstock

Third possibility -

It is also entirely possible that both of these changes are happening at the same time.

© Shutterstock

Driving the changes -

In terms of what is driving these changes, scientists believe it could be the gravitational pull of the mantle or material flowing in the outer core.

© Shutterstock

Unknowns -

And in terms of how these changes may affect the rest of planet Earth and the lives of the people who inhabit it, well, nothing is certain.

Sources: (CNN) (Science News) (Live Science)

See also: Earth has a second moon

© Shutterstock