Earth’s core seems to mysteriously wobble every 8.5 years

Strange changes in different measurements of the Earth’s surface reveal periodic oscillations deep in the planet’s heart.

A research team led by geoscientists An Yachong and Ding Hao of Wuhan University determined that the Earth’s core oscillates in an 8.5-year cycle by studying minute changes in the length of the Earth’s day and the movement of the Earth’s poles.

This in turn revealed that the tilt between the inner core and mantle is only 0.17 degrees, indicating The Earth’s core is denser in the northwestern hemisphere, a strange phenomenon we see in seismic data.

The discovery could be a game-changer in our understanding of the inner workings of the world. Some geodynamic studies assume a much larger tilt, about 10 degrees; the new measurements give us a new tool to explain surface manifestations of Earth’s core behavior.

The interior of the Earth is filled with activity that is almost beyond our comprehension. We know our planet is layered, like a jaw-dropping or spherical layer cake; toward the center, it stirs and tumbles with molten rock and metal, and the deeper you go, the thicker and heavier they become.

At the center is the core, a sphere of molten metal; at the center of the core is the inner core, a hot, dense ball of solid iron about 2,450 kilometers (1,520 miles) in diameter, slightly larger than the size of Pluto.

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In many ways, the inner core is the heart of the Earth. As it slowly cools and grows, it releases heat, which is thought to contribute significantly to the spinning dynamo in the outer core.

It is a rotating, convective, electrically conductive fluid that converts mechanical energy into magnetic energy, creating a magnetic field that protects our planet from radiation, atmospheric escape, and solar wind.

So scientists are very interested in the Earth’s core, its inner core, and all the little quirks and anomalies that might have an impact on us little humans running around the surface.

Since we can’t go there directly and measure it, we have to rely on indirect measurements based on things we can observe on the surface.

We tend to think of the rotation period as fixed, with the Earth completing a complete rotation every 23 hours, 56 minutes, 4.0916 seconds, every day of the year.

But in reality, the changes that occur within the Earth produce very small changes. For example, research published last year found that the Earth’s core changes the direction of its rotation about every six years, manifested as a change in the length of the day.

In 2019, a team of scientists led by Ding noticed different periodicities in the movement of Earth’s poles. The Earth’s poles are always moving in very noticeable ways, and for a number of different reasons, leading to some very strange behavior.

But in 2019, Ding and his colleagues. Noting a small movement of approximately 8.7 years, they suggested that this may represent a wobble in the Earth’s core.

An and Ding followed this discovery by looking for variations in the Earth’s rotation that support the same periodicity. They found it. By carefully measuring each signal, they were able to map the core features that produce these phenomena.

They found that the inner core is tilted 0.17 degrees relative to the Earth’s mantle. In other words, the axis of rotation of the inner core and the mantle are not exactly aligned. They calculated that this would produce a “wobble” of nearly 8.5 years, as the two spheres rotated around slightly different axes.

The measured signal is also consistent with a sharper-than-expected density change at the boundary between the inner and outer cores. And the core appears to be unevenly dense, with one hemisphere being denser than the other.

These properties may influence the churning and rotation of the fluid outer core, producing Earth’s magnetic field.

However, there appears to be much more going on in our planet’s core than we currently understand. As our instruments and techniques improve, all we can do is continue to study the strange effects of hidden activity on the outside world.

The study was published in nature communications.