Scientists have put forward a new theory that remnants of an ancient planet, known as Theia, may still be partially intact and buried deep within Earth's mantle. This proposal, published in the journal Nature, could provide additional details to support the giant-impact hypothesis and shed light on the origins of two massive blobs hidden within Earth's mantle.

The giant-impact hypothesis is a widely accepted theory that explains the formation of the moon through a collision between Earth and a large ancient planet. However, the existence of Theia and any remnants it left behind have long remained a mystery. Scientists have found no fragments of the planet in the solar system, leading many to assume that any remnants were fully assimilated into Earth's interior.

According to the new study, molten slabs of Theia could have embedded themselves into Earth's mantle upon impact and subsequently solidified. These remnants could be located approximately 1,800 miles (2,900 kilometers) beneath the Earth's surface, resting above the planet's core. This theory could help explain the presence of two large low-velocity provinces (LLVPs) embedded deep within Earth, one beneath Africa and another below the Pacific Ocean.

The LLVPs were first detected in the 1980s and are characterized by their large size and higher density of iron compared to the surrounding mantle. These peculiar features make them stand out when measured by seismic waves. However, their origins have remained a mystery until now.

Lead author of the study, Dr. Qian Yuan, a geophysicist and postdoctoral fellow at the California Institute of Technology, had a breakthrough moment during a seminar in 2019 when he learned about Theia and the LLVPs. Inspired by this information, he began to delve deeper into scientific studies to explore the possibility of the LLVPs being remnants of Theia. Finding no previous proposals on this subject, he developed his hypothesis.

Initially, Yuan faced rejection when he submitted his research paper proposing this idea. However, he eventually found the necessary research and modeling techniques to support his theory. The study used higher-resolution modeling to simulate the collision between Theia and Earth, showing that if Theia was of a certain size and consistency and hit Earth at a specific speed, it could leave behind remnants within Earth's mantle that align with the density of the LLVPs.

While the study offers a compelling case, there may be reluctance within the scientific community to fully accept this novel concept. Dr. Seth Jacobson, an assistant professor of planetary science at Michigan State University, acknowledges the ongoing research surrounding the LLVPs and the evolving tools used to study them.

Dr. Steve Desch, a study coauthor and professor of astrophysics at Arizona State's School of Earth and Space Exploration, believes that this work is compelling and makes a strong case. However, he also acknowledges that this hypothesis is an idea and a welcome invitation for further research and exploration into the origins of the LLVPs.

The study involved collaboration among researchers from various institutions, including Arizona State, Caltech, the Shanghai Astronomical Observatory, and NASA's Ames Research Center. As scientists continue to explore this intriguing theory, further investigation and advancements in research techniques may ultimately reveal the truth about the mysterious remnants of Theia hidden deep within Earth's mantle.