Given the vastness of the universe I'm sure there's all sorts of planets and stars that are still yet to be discovered, but scientists actually think they've found one of them right under our noses.
Literally - it's under the ground we walk on.
The theory comes in a theoretical article published in the journal Nature, in which researchers put forward their evidence that an ancient planet named Theia could have helped form Earth as we know it today.
Long before humans came along, Theia is thought to have crashed into the Earth more than four billion years ago, causing the planet to essentially become lodged into the lump of rock we call home.
The theory goes that the impact of the blast shot magma from Earth's mantle into space, and consequently formed the moon.
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Though the theory is just that - a theory - at the moment, scientists have suggested that Theia may have helped continents to form, and that the fragments of the ancient planet have impacted volcanic activity on Earth.
Researchers believe they found fragments of Theia when seismologists discovered two continent-sized 'basal mantle anomalies' - blobs beneath the Earth's crust to you and me - beneath the Pacific and Africa.
These 'anomalies' are denser than their surroundings, which suggests they're made out of different material to the rest of the Earth's mantle.
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By observing the anomalies in the Earth's mantle and comparing them to matter surrounding them, the researchers suggested that they may be buried remnants of Theia mantle material that have been preserved deep in the Earth billions of years after the moon-forming impact.
To help prove their theory, the research team used simulations to demonstrate how a part of Theia’s mantle could have entered proto-Earth’s lower mantle.
Theia is believed to have had a higher density to our Earth, so if there are moon samples which match the density and composition of the 'anomalies' believed to be Theia, it proves the theory that Theia once crashed into Earth which created our moon.
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As well as this, researchers noted there are crystals on the moon, called zircon crystals, which are also found on Earth, and on Mars.
The team wrote that Theia’s matter surviving deep within Earth would ‘be a natural consequence of the Moon-forming giant impact’.
They concluded: “Because giant impacts are common at the end stages of planet accretion, similar mantle heterogeneities caused by impacts may also exist in the interiors of other planetary bodies.”
Emily Brown