Relics of an alien planet might be under our feet, scientists say

‘Theia’ collided with Earth billions of years ago and created the Moon – but that wasn’t all, new computer simulations suggest

Relics of an ancient planet might be hiding under our feet, according to new research.

Some scientists believe that a “protoplanet” named Theia collided with Earth some 4.5 billion years ago. That collision tore off part of our planet which went on to form the Moon, they believe.

But that wasn’t all. Some pieces of Theia stayed around and may have been buried deep within the mantle of Earth, researchers believe.

That is based on new computer simulations of the collision that are reported in a journal article published today.

Researchers believe that explains two large parts of the Earth’s mantle, some 2,900km down, that do not seem to move as quickly as others. Those regions appear to be 2-3.5 per cent denser than the areas that surround them, and scientists refer to them as the “large low-velocity provinces”, or LLVPs.

Those dense parts are to be pieces of Theia’s own mantle that were preserved deep in our Earth after the collision, the researchers believe. The vast chunks of alien planet stretched tens of kilometres across and sunk deep down into our Earth to form those vast blobs.

Other planets might have the same mixed material in their mantles, researchers believe, since giant impacts of the kind that hit our Earth often happen as planets grow.

The findings are reported in a new paper, ‘Moon-forming impactor as a source of Earth’s basal mantle anomalies’, published in Nature.

The idea that the Moon was formed by a crash with an ancient planet is somewhat controversial: there is little direct evidence for it, and some material taken from the Moon has challenged the idea. But it accounts for some key parts of the Earth and the Moon, such as the relatively small core at the centre.