(CNN) — Scientists widely agree that the planet is ancient has crashed Against the Earth as it was forming billions of years ago, spewing debris that collected into the moon that adorns our night sky today.
This theory, called the giant impact hypothesis, explains many basic features of the Moon and Earth.
However, there is a clear mystery at the heart of this hypothesis: what happened to Thea? There is no direct evidence of its existence. No remains of the planet were found in the solar system. Many scientists assumed that whatever Theia left behind on Earth was mixed with the fiery caldera inside our planet.
However, a new theory suggests that the remains of the ancient planet are still partially intact, buried beneath our feet.
Theia’s molten plates may have been embedded in Earth’s mantle after the collision before solidifying, leaving bits of the ancient planet’s material lodged in Earth’s core about 2,900 kilometers below the surface, according to a study published on Wednesday. In the journal Nature.
A bold new idea
If the theory is correct, it will not only provide additional details to complete the giant impact hypothesis, but it will also answer a lingering question for geophysicists.
They already knew that there were two different masses embedded deep within the earth. The two blocks, called large low-velocity provinces or LLVPs, were first discovered in the 1980s, one lying under Africa and the other under the Pacific Ocean.
These spots are thousands of kilometers across and may have a higher iron density than the surrounding mantle, making them prominent when measured by seismic waves. But the origin of these spots, each of which is larger than the moon, remains a mystery to scientists.
For Dr. Qian Yuan, a geophysicist and postdoctoral fellow at Caltech and lead author of the new study, his understanding of LLVPs changed forever when he attended a symposium in 2019 at Arizona State University, his alma mater. The giant impact hypothesis has been identified.
That’s when he learned new details about Theia, a mysterious projectile that supposedly struck Earth billions of years ago.
As a geophysicist by training, he was aware of these mysterious spots hidden in the Earth’s mantle.
Yuan had a eureka moment, he said.
He immediately began examining scientific studies, to see if anyone else had suggested that LLVPs could be parts of Theia. But no one did.
At first, Yuan only told his theory to his advisor.
“I was afraid to go to other people because I was afraid they would think I was too crazy,” Yuan said.
Yuan first proposed his idea in a paper he submitted in 2021, but it was rejected three times. Reviewers said it lacked sufficient modeling for the giant effect.
Then he met scientists doing the research Yuan needed.
Their work, which assigned a specific size to Theia and collision speed in the modeling, suggests that the ancient planet’s collision may not have completely melted Earth’s mantle, allowing Theia’s remnants to cool and form solid structures rather than mixing into Earth’s inner soup.
“The Earth’s mantle is rocky, but it’s not solid rock,” said Dr. Steve Desch, study co-author and professor of astrophysics at Arizona State’s College of Earth and Space Exploration. “It’s this high-pressure magma that’s kind of sticky and has the consistency of peanut butter, and it’s basically sitting on a very hot stove.”
In that environment, if the material that makes up the LLVPs is too dense, it won’t be able to pack into the rough formations in which they appear, Desch said. If its density is low enough, it will simply merge with the mantle.
The question was: What is the density of the matter left behind by Theia? Can it match the density of LLVPs?
(Desch wrote his own article in 2019 in which he sought to describe the density of matter that Theia could have left behind.)
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 added: If Theia were of a certain size and consistency and collided with Earth at a certain speed, the models showed that it could actually leave behind huge chunks of its internal entrails in Earth’s mantle. Earth would also generate the remnants that would give rise to our Moon.
Building a theory
The study Yuan published this week involved co-authors from various disciplines and institutions, including Arizona State, the California Institute of Technology, the Shanghai Astronomical Observatory, and NASA’s Ames Research Center.
When asked whether he expected to encounter opposition or controversy over such a new concept — that slabs of material from an ancient extraterrestrial planet are hidden deep within the Earth — Yuan replied: “I also want to stress that this is an idea, it is a hypothesis.
“There is no way to prove that this is the case,” he added. “I invite others to do this (research).”
“This work, in his view, is compelling. It’s a very strong argument,” Desch added. He said it seemed “fairly obvious in retrospect.”
However, Dr. Seth Jacobson, associate professor of planetary science at Michigan State University, acknowledged that the theory may not gain widespread acceptance soon.
“These (LLVPs) are a very active area of research,” said Jacobson, who was not involved in the study. “The tools used to study them are constantly evolving.”
He added that the idea of Thea creating LLVPs is certainly an exciting and fascinating hypothesis, but it’s not the only one out there.
Another theory, for example, posits that LLVPs are actually masses of oceanic crust that have sunk deep into the mantle over billions of years.
“I doubt that supporters of other hypotheses (about the formation of the LLVP) will abandon them just because this hypothesis appears,” Jacobson added. “I think we will continue to discuss this for some time.”