Most researchers agree that the Moon formed five billion years ago from debris blasted off Earth in a giant impact. Scientists presented some new evidence supporting the theory that Moon was, indeed, born of a cataclysmic collision between worlds 4.5 billions of years ago.
In 1975. Journal Icarus, published a paper that suggested the hypothesis of the moon’s origin by two PSI senior scientists – Dr. William K. Hartmann and Dr. Donald R. Davis. Giant Impact Theory suggested that growing smaller planetary body (Mars-sized protoplanet) hit Earth about 4.5 billion years ago, blowing out rocky debris that was captured into orbit around Earth and coalesced into the moon. When the giant impact happened, Earth’s iron core had already formed.
The impactor itself also had an iron core which melted on impact and was added to Earth’s core. Some of the debris from the rocky mantles of both Earth and the impactor was ejected into orbit, forming the much smaller Moon.
Because so little metallic iron was blown out to orbit, the Moon ended up with a tiny core. And new findings support this hypothesis. The lunar rock samples matched the rocks from Earth’s crust and mantle, but bore no resemblance to the Earth’s interior rock.
The giant impact theory proponents say that Earth had a companion planet around it, placed at a Lagrangian Point (L5 or L4 supposedly).
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| The "Big Splat" theory of the moon's origin |
The hypothetical protoplanet Theia was in almost the same orbit of Earth (but 60º out of phase from Earth). Theia as a planet was still growing in size through accretion of matter.
Its earlier non-perturbed orbit kept it a safe distance away from Earth. However, as its mass increased through accretion, over a period of 20 to 30 million years, its orbit was destabilized and became increasingly erratic, taking it dangerously close to Earth. 4.53 billion years ago, the increasingly eccentric orbit of Theia lead to its collision with Earth at a very oblique angle.
As the two planets collided they stuck together. This led to generation of an immense amount of heat, which led to the melting and sinking of Theia’s Iron core into Earth’s core, sending a significant amount of Theia’s and Earth’s crust, as well as mantle into orbit around them. Almost half of this molten debris coalesced to become our Moon.
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