An alien planet inside the Earth sounds like the stuff of science fiction comics. An alien culture living within us. Maybe the stuff of nightmares as well.

     In 2016, University of California researchers proposed that our Earth could actually be the result of two planets that fused together after colliding: They named the other planet Theia. They also said they believed the two planetary masses mixed together uniformly when they collided and fused.

     In new research from Arizona State University, other scientists agree that our current Earth was formed after a Mars-sized rogue planet known as Theia collided with the original “earth”, but they disagree with the idea that the two masses mixed uniformly. They speculate that there are identifiable, intact, chunks of the alien planet that still exist in our Earth’s interior. They also believe that the Moon was formed from the same impact of the original earth and Theia.

     The Arizona State University scientists believe that the mantle of the planet Theia was denser than that of the original “earth”, and that allowed chunks of Theia’s mantle to sink to the bottom of the new Earth’s mantle. They are still there, in distinct thermo-chemical piles that can be identified through seismic activity.

     These alien chunks are not small. They are the size of current-day continents and are called “Large Low Shear Velocity Provinces (LLSVPs).” Don’t ask how they came up with that name?

     The Arizona State scientists have modelled the process by which these chunks could have sunk into current Earth’s lower mantle.

     In an interview, the lead scientist QianYuan, said he did a very easy calculation where he compared the size of the LLSVPs (alien chunks) to the mantle of Mars, because Theia was believed to be very similar to Mars. The total mass of the moon, together with the LLSVPs, is almost exactly the size of Mars’s mantle. The chances of that being a coincidence are infinitesimal.

     The scientists asked themselves the question: “How has the denser Theia mantle stayed intact, inside the Earth’s mantle, for billions of years? Their answer is that it’s a function of the way Earth’s mantle works, where convection circulates materials that are of a certain temperature and density. The Theia materials are so dense that they sank and never floated back up into the convection zone. They said we should think of this like the stuff that accumulates in a sharp corner that’s hard to reach with the vacuum cleaner.

     The “continent-sized” alien areas are the largest portions of Earth’s interior, so understanding how they formed, and how they continue to exist, could substantially increase our knowledge of or Earth.        

     The two largest portions of Theia, and they’re huge, are located, separately, under West Africa and under the Pacific Ocean. They are both hundreds of miles thick.

     There could also be interesting parallels drawn between these dense mantle portions and the moon because they shared a common origin.

     This is exciting because how often can you compare one 4.5-billion-year-old rock sample that’s orbited in space – the Moon – and another that’s sunk into the center of Earth?

     It’s a scientific dream come true.

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