Earth's inner core is more like a ball of butter than a solid metal sphere, a new study suggests

• Scientists have long thought Earth's inner core is like a huge solid metal ball.
• But an experiment revealed it may be a lot softer — more like butter, a lead scientist said.

A new study challenges the long-held assumption that Earth's inner core is hard, like a solid metal sphere.

Instead, our planet's heart is likely much gooier than previously thought, "kind of like how butter is soft in your kitchen," said Sichuan University's Youjun Zhang, a lead author on the study, in a press release from the University of Texas

The findings could help explain some of our planet's long-standing mysteries, like why Earth's magnetic field constantly defies expectations.

We've never seen the Earth's core

There's no way for us to sample the very insides of the Earth directly. We can't drill that far down and even if we could, human instruments would struggle to cope with the temperatures and intense pressure further into the planet.

That's why scientists usually rely on information they can glean from shockwaves that spread from earthquakes.

By looking at how these waves ping off of structures inside our planet, they can infer what's happening in there.

Coupling this seismic data with computer models, scientists had previously predicted the pressure at the very center of the Earth was so intense that the iron atoms found there were forced into solid form, in spite of the scorching temperatures.

Per these models, the atoms were stuck together in a hexagonal pattern — meaning there was effectively a huge solid metal ball at the heart of our planet (the inner core), swiveling in a pool of molten metal (the outer core).

It turns out, however, that's not the whole picture.

The Earth's inner mush revealed

A 2021 study had already started to question the big-iron-ball assumption. Seismic waves, they found, weren't really going through the Earth in a way consistent with a fully solid core.

"The more that we look at it, the more we realize it's not one boring blob of iron," said Jessica Irving, a seismologist at the University of Bristol in England, to Live Science in 2021.

The new study, published Monday in the peer-reviewed journal Proceedings of the National Academy of Sciences, sought to solve this puzzle.

It recreated the intense pressure and temperature conditions found in the inner core inside a lab, and combined that data with a much more advanced computer model.

They found that the atoms were indeed stuck in a hexagonal pattern.

But, surprisingly, individual iron atoms were still able to shift around inside that pattern — like guests moving around a dinner table, per the press release.

"The big discovery that we've found is that solid iron becomes surprisingly soft deep inside the Earth because its atoms can move much more than we ever imagined," said Zhang.

Knowing what is going on inside the Earth can help protect us

There's more to this finding than the satisfaction of understanding our planet better. Knowing what is going on inside the Earth is crucial to figuring out its mysterious magnetic field, which protects us from space radiation and pins down our atmosphere.

Thinking of the magnetic field, you may be picturing orderly concentric rings, like the layers of an onion.

But it turns out our magnetic field is a lot more complex than that. It shifts, sometimes flips, and is peppered with mysterious dents that we can't quite understand.

Because the magnetism of our planet stems from how the molten metal in the Earth's core swishes around, knowing exactly how the inner core behaves is crucial to cracking the mysteries of our magnetic field.

"Now, we know about the fundamental mechanism that will help us with understanding the dynamic processes and evolution of the Earth's inner core," said Jung-Fu Lin, a professor at the UT Jackson School of Geosciences and one of the study's lead authors, in the press release.