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Did a Giant Crash Create Earth’s Moon? Unveiling the Theia Impact Theory

There is a Titan goddess named “Theia” in ancient Greek mythology. According to legend, Theia and her brother Hyperion gave birth to three children: Helios, the Sun God, Selene, the Moon Goddess, and Eos, the Dawn Goddess. According to this myth, Theia is the creator of Selene, the “moon goddess”, and it was she who gave birth to Selene. In the field of astronomy, when people talk about the origin of the moon, they will think of the name “Theia”, which refers to a mysterious planet that people speculate. It is said that 4.5 billion years ago, there was a “protoplanet” in the original solar system. It was a kind of “planetary embryo”, which was composed of very small planetesimals called “planet particles” that collided with each other under the influence of gravity. Become. Under the disturbance of surrounding celestial bodies, protoplanets gradually formed real planets through mutual collision and aggregation.

The protoplanet 4.5 billion years ago was about the same size as Mars today. Due to the gravitational pull of surrounding celestial bodies, it accidentally left its original orbit and collided with the Earth. The collision was extremely violent and was enough to melt a considerable part of the Earth. Harmonize.

As a result, part of the earth was thrown into space, and the protoplanet was also broken. The fragments of the two circled around the earth together and aggregated into the earth’s satellite, the moon. Since the hypothetical protoplanet created the moon through collision, scientists named it “Theia” after the mother of the “Moon Goddess”.

According to computer simulations, the moon was very close to the earth when it was first born, only about 20,000 kilometers away from the earth. But after 4.5 billion years of gravitational and tidal effects between the earth and the moon, it has now moved to a position 380,000 kilometers away from the earth.

This description of the birth of the moon is just a conjecture, known as the “big collision theory.” Together with three other hypotheses about the origin of the moon, it forms the famous “four major hypotheses” to explain the origin of the moon. The remaining three hypotheses are the “homology theory”, “split theory” and “capture theory”. Among them, the “same origin theory” believes that the earth and the moon are both formed by the accretion of nebulae in the solar system; the “split theory” believes that the moon is formed from a part of the material thrown out by the earth; and the “capture theory” believes that the moon is “Captured” by the Earth as it approaches the Earth.

Although each of the four hypotheses is reasonable, none of them has been finally confirmed. However, many scientists believe that at present, the “big collision theory” is the most credible, but the “big collision theory” has not been confirmed either. Did “Theia” really exist? Did a big collision really happen?

Plate movement started

If the “big collision theory” is true and credible, then it will definitely affect the evolution of the earth in a way different from that described by the other three hypotheses.

Recently, scientists have conducted further research on the “big collision theory” through computer simulations. They found that the collision not only explained how Earth got its moon, but also provided a succinct explanation for the movement of plate plates on Earth. And, if this explanation is accurate, it could help astronomers discover worlds with plate motions similar to Earth’s around stars other than the Sun.

Explorations so far suggest that plate tectonics may be rare in the universe, because of all the worlds discovered so far, ours is the only one known to have plate tectonics.

It turns out that our planet is indeed special. We now know that Earth’s moving plates have been drifting, colliding and “subducting” for billions of years. These movements created and split continents, pushed up mountains, and widened oceans.

At the same time, such movements also erase much of Earth’s early history, including how and when plate movement occurred. Scientists have been looking for answers. They want to understand the mysteries of the movement of plate plates on the earth. Qian Yuan, a scientist at the California Institute of Technology, studies how the Earth’s inner layers move and affect the surface. His research team believes that the way the Earth holds the moon provides a simple and clear explanation for the origin of plate movement.

The researchers focused on two clumps of material deep in the Earth’s mantle, each as large as a continent. Previously, scientists thought they were old tectonic plates sliding deep into the Earth. However, Qian Yuan’s research team believes that these mysterious materials may be the remnants of high-density materials on “Theia” sinking into the mantle. To this end, these scientists used computers to simulate the impact of “Theia” on the Earth, and how the material “Theia” sank into the Earth’s interior affected the movement of rocks inside the Earth.

Simulation experiments show that when the remains of “Theia” sink to the bottom of the Earth’s mantle, these hot material clumps will cause a large amount of equally hot rock to climb upward, and they will be pulled into the Earth’s hard outer material. As they rise and expand, the plates on the Earth’s surface are instead pushed beneath the Earth, sliding into the mantle, a process scientists call “subduction.”

Subduction is the main characteristic of plate motion. Based on simulations, the researchers believe that plate movement characterized by subduction should have started about 200 million years after the moon formed. At that time, large clumps in the mantle may have initiated subduction. But it is not yet completely certain whether those lumps really came from “Theia”. Lauren Montesi, a scientist who studies planetary surface movements at the University of Maryland, College Park, believes that it is too early to conclude that “Theia” triggered plate movement.

The moon’s contribution to the earth

If the conclusions based on the simulations prove correct, then the search for Earth-like planets outside the solar system will bring about a new focus, and that is plate motion. The researchers explained that this situation shows that if people find an Earth-like planet with a large moon in the universe, then they have reason to believe that the planet may have once had a large impactor, and this kind of The presence of impactors could also mean that the planet has plate motions. Obviously, more attention in this area will hopefully help humans discover another world with plate movements like our own.

Now we know that the impact of plate movement on the earth is precious, because it is the plate movement that shapes the earth into a place suitable for life. The plate movement started the cycle of water, carbon and oxygen, injecting endless cycle of vitality into the earth, thus shaping the earth into a vibrant life planet.

From this point of view, it is very likely that the impact of “Theia” on the earth was an epoch-making important event in the history of the earth. About 4.5 billion years later, the fate of the earth was completely changed. It eventually became a unique planet of life, a cradle of civilization that produced great wisdom. This shows that the initiation of plate movement is very important.

In addition, “Theia” has an even more valuable contribution to the earth: it brought the moon to the earth. What would the earth be like without the moon? Without the moon, Earth’s gravity would be much less and we would weigh less. Precisely because the collision brought about one-tenth of the material on “Theia” to the earth, the earth’s gravity is not that small, and our weight is not that light. More importantly, if it hadn’t been for that event, we might not have had the chance to come to Earth at all, because without the moon, the evolution of life would have been much slower. Because the newborn moon is extremely close to the earth, the tidal force it triggers is much stronger than today. This huge tidal force causes seawater to wash away at the continent, filling the ocean with minerals from the land, forming the so-called “moon” that prompted the birth of life. Primordial Soup”. In addition, if there were no stabilizing effect of the moon on the earth’s rotation axis, our earth would probably lie on the orbital plane like Uranus, that is, the rotation axis and the revolution axis would be relatively vertical. In this way, sunlight will move back and forth between the poles in a year, and all life on earth will have to migrate back and forth between the North and South Pole every year in pursuit of sunlight.

Looking for the “predecessor” of “Theia”

So, was the moon really “created” by the collision of “Theia”? In order to figure out this problem, scientists have made a lot of efforts. They believe that to answer this question, people must first obtain evidence of whether “Theia” really existed. Scientists believe that if “Theia” did exist, then there would have been some asteroid-sized polymers when the solar system was still young. They are called “planetites” and were the original materials that made up “Theia” , some of which should still exist today at the Sun-Earth (Sun and Earth) Lagrange points.

The so-called “Lagrangian point” is actually a gravitational balance point in space. It usually exists between two large celestial bodies. Due to the influence of the gravity of the two celestial bodies, small objects located at this point can remain relatively balanced. . There are theoretically five Lagrangian points between every two large celestial bodies, such as the sun and Jupiter, the sun and the earth, and the earth and the moon. These five Lagrangian points are represented by L1, L2, and L3 respectively. , L4 and L5 represent. Those “drifters” in space tend to collect at Lagrange points, like water collecting at the bottom of a well.

After the collision, ancient “Theia” apparently no longer exists, but some “planetites” may still be in the place where it was formed. They were originally supposed to be part of “Theia”, but they failed and were left behind. Therefore, if people can find some small celestial bodies similar to asteroids there today, then they are likely to be “planet particles” left over from that year. If this is proven by analyzing their material composition, then the “big collision” theory can be confirmed.

Therefore, the most direct and effective way to solve the mystery of “Theia” is to find those small celestial bodies and bring the materials on them back to Earth. Although such a space mission is complex, it should rely on current human space technology It can be implemented. In fact, as early as 2009, two almost identical Solar-Terrestrial Relations Observatory (STEREO) satellites entered the edge areas of the Sun-Earth Lagrange points L4 and L5 respectively, but they did not find any suspicious targets. . Originally, the “Solar-Terrestrial Relations Observatory” was to observe the sun, but they happened to pass by the Sun-Earth Lagrange points L4 and L5 respectively, so scientists incidentally asked them to perform such an additional task. These scientists believe that if that ancient planet really existed, there should be some debris left behind, and it should be possible for the Solar-Terrestrial Observatory to discover them.

However, such a search is not easy, because the Lagrangian point is not an infinitesimal point in space, but actually has a considerable area. In such an area, just one or two searches cannot explain the problem, so it is still impossible to judge whether “Theia” really existed. To this day, the mystery of “Theia” still has no answer. People expect that more diverse forms of exploration in the future will solve this important unsolved mystery.

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