How the origin of the Moon was revealed by science

It lights up our nights, moves our tides and our romances. The Moon, our cosmic companion, has always fascinated humanity, inspiring myths, legends, songs and passions. But, beyond its poetic charm, the Moon is also an object of scientific study that is fundamental to understanding the history of our planet and the Solar System. And one of the enigmas that most intrigues scientists who study the star is: how was the Moon formed?

Throughout history, several myths and theories have attempted to explain the origin of our natural satellite. In Finnish mythology, the Moon is said to have emerged from the white of a duck egg that Ilmatar, the Goddess of the Air, dropped. For the Eskimos, the Moon is said to have been a young girl who fled to the sky to escape the harassment of her brother who was always chasing the girl. Here in Brazil, the Tupis believed that the Moon was created by Tupã to illuminate the darkness of the night that he had just created.

Today we know that the Moon was probably formed from a colossal impact that occurred in the early days of the Solar System. But this story was not invented by some creative mind like the mystical legends told by our ancestors. It can only be told today thanks to centuries of study, determined scientists, technological development and an unparalleled adventure!

When something like the formation of the Moon cannot be observed or reproduced in a laboratory, Science works by raising hypotheses and seeking evidence that can reinforce, prove or discard one idea or another.

Some hypotheses then emerged, such as the Fission hypothesis, which proposed that the Moon had separated from the Earth due to the rapid rotation of our planet. An interesting theory, but one that is not supported by mathematics. Calculations showed that for this to happen, the Earth would have to spin faster than a figure skater.

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Another theory, the Capture theory, suggested that the Moon, wandering through the Solar System, had been captured by Earth's gravity and become our companion. This was a valid idea, but it had difficulty explaining the Moon's nearly circular orbit and the fact that it was moving away from our planet every year.

The Coaccretion Theory argued that the Earth and the Moon would have formed together, from the same disk of dust and gas that gave rise to the Solar System. A simple theory that was one of the most accepted by the scientific community until the middle of the 20th century, but it lacked evidence to prove it, and that is where this story meets the story of humanity's greatest adventure.

The best way to try to understand the origin of the Moon would be to go there and bring back a piece of it for our scientists to analyze. And it was when Armstrong, Aldrin and Collins returned from their epic voyage in 1969 that the mysteries of the Moon's formation began to be unraveled.

The rocks brought back by Apollo 11 and five other missions that landed on our natural satellite showed a great similarity to terrestrial rocks. This not only ruled out the Capture Theory, but also was the starting point for the resurgence of a revolutionary theory for the origin of the Moon: the Giant Impact Theory.

This theory for the origin of the Moon was first proposed in 1946 by Reginald Daly of Harvard University. He suggested that the Moon could have formed from an impact of a large object with the Earth. This theory did not gain much attention until it was revived in 1975 by scientists William Hartmann and Donald Davis.

They suggested that the Moon formed 4.5 billion years ago from debris left over from a collision between the early Earth and another Mars-sized planet, later named Theia. The energy released in the impact vaporized part of the Earth's crust and hurled a huge amount of debris into space. Over millions of years, this debris coalesced to form the Moon.

The Giant Impact Theory was a perfect fit to explain several characteristics of the Moon, such as its inclined orbit, its chemical composition similar to that of Earth and distinct from other known objects in the Solar System. The Moon is composed essentially of silicate rocks equivalent to those found in the Earth's mantle, but it has an iron core four times smaller than that of our planet, which would rule out the Coaccretion hypothesis.

Even though the event was not reproduced in the laboratory, computer models that simulated the impact between Earth and Theia reinforced the plausibility of the theory. But the definitive proof came from samples of lunar rocks brought back by the Apollo missions between 1969 and 1972.

In addition to the chemical similarities between lunar and terrestrial rocks, the low quantity of volatile elements, such as water, in the samples brought from the Moon, reinforced the idea of ​​a colossal impact that would have vaporized these elements.

The Apollo missions also left scientific instruments on the Moon that continue to provide valuable data about the internal structure of our satellite, such as seismometers that detect “lunar tremors”, allowing scientists to study the composition and geological history of the Moon.

The Giant Impact Theory revolutionized our understanding of the formation of the Moon and the Solar System itself. But Science continues! Recently, new simulations have shown that this process may have been much faster than previously thought. The Moon would have formed just a few hours after the impact with Theia. An efficiency that would make even Chinese contractors envious.

The history of the formation of the Moon is an example of how Science, driven by human curiosity, seeks to unravel the mysteries of the Cosmos and better understand our place in the Universe. And if the Moon has always attracted humanity's attention, with Science it becomes even more fascinating and captivating!