Fragments Of The Planet That Formed The Moon May Be Buried By The Earth's Core

New research now suggests that Theia is not completely gone – huge chunks of it might still exist inside our planet. Image Credit: Pavel Gabzdyl/

The Moon is believed to have formed in a gigantic impact when a Mars-sized planet collided with the primordial Earth. This object is nicknamed Theia, after the Titaness and goddess of precious metals and gems, and mother of the Selene (the Moon) in Greek mythology. New research now suggests that Theia is not completely gone – huge chunks of it might still exist inside our planet.

Around the Earth’s core, scientists believe that there are two large structures called low-shear velocity provinces (LLSVPs). One is underneath west Africa and the other underneath the Pacific. They are 1,000 kilometers (600 miles) thick and stretch for several thousand kilometers. Some researchers now believe that these blobs are chunks leftover by Theia.

“This crazy idea is at least possible,” Qian Yuan, a PhD student in geodynamics at Arizona State University told Science. Yuan presented his research at the 52nd Lunar and Planetary Science Conference last week.

Animation of LLSVPs based on the clustering analysis of Cottaar & Lekic (2016).  Image Credit: Sanne.cottaar/Wikimedia CommonsCC BY-SA 4.0

The idea that these structures were pieces of Theia has been discussed before, but this new work combines several pieces of evidence in a coherent scenario. Theia merged with Earth, and their cores combined into one. Simulations ran by the researchers show that Theia’s mantle was a bit denser than Earth’s own, and this would allow a large portion of its mantle to survive. The range from the simulations suggests rocks 1.5 to 3.5 percent denser than Earth’s own. Previous studies have suggested that the LLSVPs density is within that range.

The simulation also suggests that Theia might be bigger than previously thought – maybe as big as Earth. After all, the LLSVPs contain six times more mass than the whole Moon. So the impactor, if these structures are from outer space, must have been quite massive.

While the evidence presented provides a nice picture, there are many questions still open regarding these structures that might impact this interpretation. The interior of our planet is studied using seismic waves and models, so there could be errors lurking in there, creating a less than precise view. The LLSVPs might not be as thick or dense or built in the way we believe they are. So a big dense Theia might not be behind these blobs.

The work has been submitted for peer-review to Geophysical Research Letters and it will certainly continue to be discussed. The LLSVPs are a source of continuous interest. They have been even considered as a potential source of a future super eruption.  


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