Chunks of an alien world could be hidden deep within our planet, say scientists

• Scientists think a planet may have crashed into Earth 4.5 billion years ago, creating the moon.
• This alien planet, Theia, was thought to have completely disappeared in the collision.
• A new study suggests parts of Theia still exist in our planet, around Earth's core.

Continent-sized chunks of an alien world may be hiding deep within our planet — and it could explain the weird structures that appear to be surrounding Earth's core.

Scientists have long hypothesized that a Mars-sized planet called Theia crashed into Earth 4.5 billion years ago, leading to the creation of the moon.

But this theory has been difficult to prove, in part because Theia was long thought to have disappeared during the collision.

Now a supercomputer simulation provides evidence that chunks of Theia may still survive in the boundary between our planet's mantle and the core.

As well as shedding new light on the inner workings of our planet, scientists hope they will one day have access to these slabs of alien rock to reveal, once and for all, how our moon formed.

A 4.5 billion-year-old mystery

Despite all of our technological advances, we still don't know exactly how the moon was created.

The leading theory among planetary scientists is called the "giant impact" hypothesis, whereby a theoretical planet called Theia barreled into the early Earth at its very beginning.

According to this theory, the collision caused rocks to spray into the cosmos, some of which started swirling together in Earth's orbit, ultimately leading to the creation of the moon.

The whole process may have taken under a day, per a 2021 study.

The problem is that this is very difficult to prove: we only have secondhand evidence that Theia existed. The assumption has long been that Theia melded into moon, the Earth's mantle, and its core, in effect disappearing completely.

But this new study offers hope that parts of the alien planet survived at the heart of the Earth.

Theia may be behind a mysterious anomaly in Earth's mantle

There's a very bizarre region inside the Earth's mantle that scientists haven't been able to explain: this is called the core-mantle boundary.

Right at the limit between the mantle and the core, the temperature shoots up. And seismic waves — which are used by geologists to get a sense of what is going on inside our planet — mysteriously slow down.

This has prompted scientists to think there may be something wrapped around the core, some unexplained layer, that keeps the very heart of our planet warm.

Previous theories have suggested this core-mantle boundary could be made up of bits of ancient ocean floors. But some things don't quite line up.

For instance, some lava that is found at the surface, which is thought to have traveled from the core-mantle boundary, is believed to be 4.5 billion years old — or about as old as the collision.

That's likely too old to belong to an ocean floor, Hongping Deng, a professor of computational physics from the Chinese Academy of Sciences, and the lead author on the study, told Insider Wednesday.

Previous research had also found that ancient lava from magma plumes in Iceland and Samoa carried bizarre radioactive signatures that would make more sense if they came from the ancient alien planet. The findings suggested parts of Theia, that could be millions of times larger than Mount Everest, could have sunk deep in our planet's mantle.

This prompted Deng and his co-authors to investigate whether the mysterious boundary could be, at least in part, made up of old bits of Theia using one of the most advanced computer simulations of the collision ever designed.

This simulation tracked 100 million virtual particles from the moment Theia would have crashed into the Earth through to millions of years later, study author Vincent Eke, a professor of cosmological computing at Durham University, UK, told Insider.

"The biggest simulations that we run, they will be going for a few months on a supercomputer," he said.

Using these simulations, the scientists were able to show that some fragments of Theia — roughly 2% of the whole mass of the Earth —could have survived inside the Earth, slowly sinking through the mantle, said Deng.

These line up suspiciously with the location of the core-mantle boundary today, he said.

"One of the most exciting things is that Theia, this body that is supposed to have smashed into the early Earth, is becoming more tangible," Christian Schroeder, a planetary scientist at the University of Stirling who was not involved in the study, told Insider Tuesday.

"It's exciting to see that it is becoming real and there's something we can investigate," he told Insider.

Clues to cracking the case are locked in the mantle

The findings, published in the peer-reviewed journal Nature, provide hope that a sample of Theia could still be lurking inside our planet.

"It means that if you dig enough in the Earth, we can find something that's not belonging to Earth," Deng said.

The problem is that the core-mantle boundary is very far from the surface — about 1,800 miles. And even if we were able to dig that deep, the punishing temperatures and crushing pressure would likely destroy any tools that we would attempt to send down there for sampling.

Still, the peculiar lava that could come from Theia may provide clues about its composition.

Deng also hopes the simulation can be pushed even further — and could eventually even allow us to understand where Theia came from, how it traveled through time, and what the early solar system looked like.

Deng, however, warns that more research is needed to confirm whether hypothesis in the paper is correct.

"It's a very bold idea, I'll give you that. [Bringing] something that's 4.5 billion years old to present-day Earth is crazy," said Deng.

"If everything pulls together, then that would be amazing. If it doesn't, that's science," he said.