Probably, the Moon was born from a blow that the Earth took. More than 4 billion years ago, our planet would have suffered the biggest impact of its existence: it collided head-on with another planet, a colossus the size of Mars that crossed its orbit. As the unsuspecting star was smaller, it ended up in shrapnel. The Earth, of course, did not escape unscathed either: much of its surface literally went into space. After a few years, the remnants of the explosion came together to form the Moon. This frightening phenomenon only happened because the solar system was forming at that time. A few million years before the big crash, there was only microscopic dust around the Sun.
The grains, over time, came together to form more voluminous rocks, which collided with each other, creating even larger bodies. The rocks that became big and strong survived as planets – among them, the one we call Earth today. Although there is still no definitive proof that the space collision really happened, this is by far the most accepted theory about the Moon’s emergence. A very strong argument in its favor is the fact that the 2% concentration of iron in the center of the satellite is practically equal to that found in the most superficial layers of the Earth – precisely those that would have been hit by the impact. “Furthermore, the composition of moonstones is very similar to that of rocks in the Earth’s mantle, the layer that lies just below the surface of the planet. It is one more point in common between the two stars”, says geophysicist Lon Hood, from the University of Arizona, in the United States.
A space megathrust 4.5 billion years ago gave rise to our satellite
A DRY PLANET
The Earth of 4.5 billion years ago was hell itself. On its surface, only rocks and a lot of lava. Liquid water, the basis for life, would only appear after hundreds of millions of years. The thin atmosphere then, formed by methane and ammonia, would be fatal for human beings. A piece of this still inhospitable planet would give rise to the Moon
1. At that time of the infernal Earth, the solar system was young and unstable, which is why many collisions between huge stars took place, like planets in formation. One of them, which was about half the size of the Earth’s globe, crashed into the rocky mass of our planet. With the hit, the intruding star shattered and the Earth lost part of its surface.
2. The explosion formed a quantity of shrapnel at least twice the mass of the current Moon. The pieces of the intruding planet that were farthest from Earth’s orbit escaped into space. Even so, half of the shrapnel was still left as raw material to form the new satellite.
3. The shrapnel that was closest to Earth was attracted by gravity and fell to the planet, helping to rebuild the outer layer of the globe. The rocky remnants that would give rise to the Moon came together as a kind of ring around the Earth’s equator. Over there, the speed of rotation of the planet is faster, which caused the particles to coalesce in that region
4. Aligned close to the Equator, the pieces united by the force of gravity, forming the Moon. Astronomers estimate that this process of lunar birth must have been very fast, taking a maximum of 100 years. Shortly after its birth, the satellite was just 25,000 kilometers away from Earth. Today, the average distance is around 380 thousand kilometers
INFLUENT COMPANION
Since its formation, the Moon has had important effects on Earth’s life. At the time of its creation, the satellite exerted such a strong gravitational pull on the planet’s rotation that it made our days last just five hours. In a few billion years, when the lunar orbit stabilizes, the days will last a month. The Moon is still the great star responsible for ocean tides and sea level variation on Earth.