the moon

Dubai, United Arab Emirates (CNN) – Most scientists agree that it is possible that an ancient planet, Theia, collided with the Earth when it was forming billions of years ago, causing a scattering of debris that resulted in the formation of the moon that decorates the night sky.

This theory, known as the giant impact hypothesis, explains many basic features of the Moon and Earth.

However, a stark mystery remained at the heart of this hypothesis: What happened to Thea? Direct evidence of the existence of this ancient planet has not been found, nor on any remaining parts of the planet in the solar system. Many scientists assumed that any debris Theia left on Earth had become embedded in our planet’s interior.

However, a new theory suggests that the remains of the ancient planet are still partially intact, buried beneath our feet.

Molten fragments of Theia could have embedded themselves within Earth’s mantle after the collision before solidifying, leaving fragments of the ancient planet’s material resting above Earth’s core about 2,900 kilometers below the Earth’s surface, according to a study published in the journal Nature on Wednesday.

A new and bold idea

If the theory is correct, it would not only provide additional details to support the giant impact hypothesis, but it would also answer a lingering question for geophysicists.

They were already aware that there were two huge points embedded deep within the earth. The two blocks were discovered for the first time in the 1980s, one of them located under Africa and the other under the Pacific Ocean.

The two points are thousands of kilometers across and are likely denser in iron than the surrounding mantle, making them prominent when measured by seismic waves. But the origins of the two points, each of which is larger than the moon, remain a mystery to scientists.

But for Dr. Qian Yuan, a geophysicist and postdoctoral fellow at Caltech, and lead author of the new study, his understanding of the two masses changed when he attended a 2019 symposium at Arizona State University that outlined the giant impact hypothesis.

In this symposium, discover new details about Theia, the mysterious object that supposedly collided with Earth billions of years ago.

As a geophysicist, he was aware of the two mysterious spots hidden in the Earth’s mantle.

He immediately began pursuing scientific studies, looking to see if someone else had suggested that the two clumps might be parts of Theia, but he found no one had come forward with that theory.

Drawing showing Theia colliding with Earth. Photo: Hernán Cañellas

Interdisciplinary research

Yuan first proposed his idea in a 2021 paper, but it was rejected three times. Peer reviewers said it lacked adequate modeling of a giant impact.

Then he met scientists who conducted the kind of research Yuan needed.

Their work, which modeled some size for Theia and impact speed, revealed that the ancient planet’s impact likely did not completely melt Earth’s mantle, allowing Theia’s remnants to cool and form solid structures rather than fusing into Earth’s inner core.

“The Earth’s mantle is rocky, but it’s not like solid rock, it’s high-pressure magma,” said Dr. Steve Desch, study co-author and professor of astrophysics at Arizona State’s College of Earth and Space Exploration.

In that environment, if the material that makes up the two masses was too dense, it would not be able to accumulate in the rough formations in which they appear. If their density is low enough, they will simply blend into the churning mantle.

The question was as follows: What is the density of the matter left behind by Theia? Can it be compatible with the density of the two masses?

Yuan said the researchers sought to create high-resolution models with 100 to 1,000 times greater accuracy than their previous attempts. However, the calculations remained consistent: If Theia were of a certain size and consistency, and collided with Earth at a certain speed, the models showed that it could, in fact, leave behind huge clumps within the Earth’s mantle, producing debris that would form the Moon.

The study Yuan published this week includes co-authors from a variety of disciplines from a range of institutions, including Arizona State, the California Institute of Technology, the Shanghai Astronomical Observatory, and NASA’s Ames Research Center.

When asked if he expected to encounter opposition or controversy over such a new concept that fragment materials from an ancient extraterrestrial planet are hidden deep underground, Yuan replied: “I want to stress that this is just an idea; a hypothesis.”

He added: “There is no way to prove that this is what happened. I welcome anyone who wants to do this (research).”

Dr. Seth Jacobson, assistant professor of planetary sciences at Michigan State University, acknowledged that the theory may not gain widespread acceptance soon.