Billions of years ago our Solar system was at its beginning; a very harsh and dirty place, filled with planetoids and a chaotic structure raging across the space of our Solar System. Collisions were something very ordinary at that point in time, and one of these collisions has to do with how are Moon actually formed; at least hypothetically. 

We are talking about Theia, a planet the size of Mars that according to some theories collided with Earth. Meeting at a very specific angle, these two planets crossed their paths which led to a catastrophic collision with the leftover debris from this gigantic impact, coalesced inside Earth’s orbit to form what is now the Moon.

Because of the specific angle at which the two planets collided, Earth was able to come out on top and survive the gigantic impact, but an entirely different scenario could have take place if these two objects met at a different angle; if the collision had been more direct, near the poles or Earths equator, our planet could have been practically obliterated together with Theia. This scenario would probably have created a short-lived asteroid belt between the orbits of Venus and Mars.

Theia formed in what is known as a Lagrange point, a gravitationally stable region in the Earth’s orbit, found at the opposite side of the Sun. Gravitation did its part and caused oscillation in the orbit of Theia, bringing this small sized planet towards Earth, until at one point, the two collided. Researchers believe that  gravitational perturbation from Venus and Jupiter actually caused the Mars-sized planet to approach and eventually impact Earth. 

Scientists believe that after the collision and the leftover debris formed around Earths orbit, two satellites were formed that orbited the Earth. These two moons eventually fusioned forming what is today Earths moon, explaining the differences between the faces of the near and far sides of the Moon. Conventional scientists don’t completely agree with the this theory.

This scenario is called Giant Impact Theory, and astronomers believe that it accurately explains the similarities of the Moon and Earth in their chemical compositions since the Moon is very similar to that of the Earth’s crust. 

Even though there are numerous theories about the moon’s formation, the Theia scenario seems more and more likely; the Apollo missions that brought to Earth lunar material seem to confirm this hypothesis more than ever before, showing a great similarity in composition to the Earth. Other theories about the formation of the moon include that somehow the Moon separated from Earth at some time and was stuck in the orbit it is today, also, scientists theorize that the Moon was captured by Earth’s gravity and brought into orbit in the distant past. But none of these theories seem to stick as much as the Giant Impact Theory and Theia. 

Researchers have found several impact crater on Earth, none of them as big as the impact with Theia. Apart of the giant impact theory, the largest asteroids known to have impact the Earth in the distant past were much smaller, at around ten kilometers in size, that probably occurred during the Late Heavy Bombardment, which took place somewhere between 4.1 and 3.8 billion years ago. 

Planetary scientists first came up with the theory of Theia in in 1969.

The largest verified crater on our planet is the Vredefort crater located in South Africa,this crater is commonly referred to as the Vredefort Dome or the Vredefort impact structure. The crater is approximately 300 kilometers in diameter, twice as big as the Chicxulub crater located near the Yucatan peninsula in Mexico that apparently caused Dinosaurs to become extinct. 

Proposed by R.A. Schmidt in 1962; there is a much larger impact crater located in Antarctica, or better said hidden beneath the ice cap of Wilkes Land, East Antarctica. This impact crater has not been verified and researched properly. If it were to be confirmed, it would become the largest known impact crater on planet Earth. 

In mythology, Theia is a Greek goddess and the mother of Selene, the goddess of the moon.

Image source: National Geographic. Reference: Wikipedia / National Geographic.