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Secrets of Ancient Impacts: Why Was This Clash Key to the Formation of the Moon?
4.4 billion years ago, in the early history of the Earth, an unprecedented impact event occurred. The Earth, which was forming at that time, unexpectedly encountered a protoplanet Theia, which was about the size of Mars. This impact not only completely changed the fate of the earth, but also ultimately led to the birth of the moon. This theory is called the "giant impact hypothesis" and is currently one of the most powerful explanations for the formation of the moon by astronomers.
The giant impact hypothesis believes that this conflict was a key event that led to the formation of the moon. At that time, the Earth collided with Theia, a planet about half the diameter, and the resulting debris eventually formed the moon today.
According to this hypothesis, Theia's collision with the Earth occurred about 4.4 to 4.5 billion years ago, which is about 10 to 20 million years after the solar system began to form. Research believes that this impact occurred at an oblique angle and at a relatively moderate speed, which was enough to eject a large amount of material into space, which then gradually condensed to form the moon.
A 2016 study showed that rocks from the moon have almost identical stable isotope ratios to rocks from Earth, further supporting the validity of the giant impact hypothesis. This evidence suggests that the moon and the earth may have had a common origin in the early days, so that the composition of the moon is quite similar to that of the earth.
“The rocks and materials mixed in after the impact make the moon’s geological characteristics similar to those of the earth. This is a fascinating astronomical phenomenon.”
Scientists also speculate that the impact may have provided the Earth and moon systems with unusually high angular momentum, which is not common among other Earth-like planets. Additionally, analysis of the Moon's internal structure shows that the Moon has a relatively small iron core, making it less dense than Earth. This all points to the high energy and specific conditions provided by the impact event that gave the Moon such unique properties during its formation.
Although the giant impact hypothesis appears to explain most of the evidence, many key questions remain unresolved. For example, the Moon has lower volatile elements that would be difficult to explain in a high-energy collision. In addition, why Venus, a planet that has also experienced huge impacts, does not have a matching satellite is another hot issue that people have discussed.
"The giant collision provided the energy needed to form the moon, but we still don't fully understand how this event affected the formation of the planets and their moons."
Starting from the theory proposed by George Darwin at the end of the 19th century, human discussion of the formation of the moon has gone through many evolutions. Darwin had hypothesized that the moon was created by centrifugal force caused by the Earth's rotation, but as time went on, Lucena Alworth Daly challenged this idea and proposed the theory that an impact created the moon. In 1974, at a special conference, this hypothesis was proposed again and gradually gained recognition from the academic community.
In short, by comparing the composition of the Earth and the Moon, modeling impact events, and studying lunar surface samples, scientists have been able to reconstruct the ancient history of the universe. Although the current research results are quite rich, dramatic turns and unsolved mysteries are still waiting for us to explore, and the true origin of the moon is still worthy of our pondering.
In addition, with the observation of signs of similar collisions in other galaxies and the continuous improvement of calculation models, will we discover more secrets related to the formation of the moon in the future?
