34 million years after his formation, the Earth were hit by a planet: resulting matter has become The Moon

In the last article I spoken about probably collisions between Earth and some asteroids called Near Earth Asteroids (NEA), but there is 1 specific collision I left out. This is probably the most important destructive event for our planet but even the most important for what its consequence. 

One simple question: how did the Moon to be formed? Most of people see it, crescent, waxing, full.. But where does it come from? Does it form itself or did it been captured?

The story of Thea

During the primordial phase of Solar System, planets formed as we know 'em today: 4 rocked planets close to the Sun, 4 gas planets on the outside and 2 belts of asteroid, the first between Mars and Jupiter (Principal Asteroids Belt), the second over Neptune (Kuiper's Belt) where you can find celestial body similar to Pluto and the short-range comets (as Halley comet). Telling the truth, probably the first Principal Asteroids Belt is the result of a exploded planet, called Minerva, but this is another story that i will tell you in next posts.

Theia is the name of an hypothetical planet formed on a Lagrange point of the Earth. A Lagrange point is a space zone where 2 big celestial bodies allow to a smaller celestial body to stay in, with a stable condition (for example you can think about Trojans asteroids of Jupiter). Every celestial body has 5 Lagrange points. Well, Thea formed in one of the Earth's Lagrange points, and he started to grow, capturing dust and matter around it. The problem was that it grew so much! In this condition, it losts the stability given by Lagrange point and he started having an unstable orbit. In less than 35 million years it collided with Earth, approximately with a 4 km/s speed and an angle of 45 degrees.

Due to its size, similar to Mars, the heaviest matter melted with Earth, but the lightest had been thrown in orbit, generating the Moon

Yes, Moon is our "daughter" and it still takes parts of Thea in its internal structure: recent studies demonstrated that oxygen isotope are different depending of rocks position: if the matter on the surface were mixed during the impact, probably the deeper rocks having heavier oxygen isotope, that were taken to the surface time after time, could have fragments of Thea inside of them.

See you next time