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The Legend of Theia: Is This Lost Planet Really the Moon's Mother?
The giant impact hypothesis has received widespread attention since it was first proposed by Canadian geologist Reginald Daly in 1946. This hypothesis has been considered as the mainstream scientific theory to explain the formation of the moon and has triggered numerous discussions about the relationship between the Earth and the Moon. According to this hypothesis, a planet the size of Mars (called Theia) collided violently with Earth in the early Earth period 4.5 billion years ago, and the ejecta caused by this impact eventually formed the Moon.
The hypothesis suggests that the Moon may have been formed by a direct impact, rather than by rotational forces as earlier theories had suggested.
Several studies have shown that the Moon's orbit is similar to the Earth's rotation, which supports this hypothesis. Additionally, rock samples from the Moon show the same stable isotope ratios as Earth rocks, further supporting the idea that they may have a common origin. However, this hypothesis still leaves some unsolved mysteries, such as: How was the moon formed after this giant impact? Why did Venus experience a similar impact but the Moon did not?
Historical BackgroundIn the late 19th century, George Darwin proposed that the Earth and Moon were once a single entity that became separated over time. However, Daly challenged this view, arguing that the formation of the Moon was more likely related to an impact. Since then, with the holding of many academic conferences, the giant impact hypothesis has gradually won wide recognition in the academic community.
According to modern theories of planet formation, Theia was once a Mars-sized body in our solar system that shared an orbit with Earth. The appeal of this hypothesis is that it explains the layout of the Moon and Earth during their formation.
The Nature of TheiaThe name Theia comes from the Titan goddess in Greek mythology, who is said to be the mother of the moon goddess Selene. The name was given to emphasize the connection between Theia and the Moon. Scientists have proposed that this hypothetical protoplanet was similar in composition to Earth, making a collision between the two more likely, leading to the formation of the present-day Moon.
"A planetary-scale impact appears to have provided the necessary kinetic energy for the assembly of the Earth and Moon."
Theoretical model and composition
Scientists believe that the collision between Theia and Earth occurred between 4.4 and 4.5 billion years ago, when the Earth was almost fully formed. Different computer simulations suggest that the impact occurred at a relatively low speed and struck the Earth at an angle of about 45 degrees. Such a violent impact not only supplied the energy needed to form the Moon, but also provided additional momentum to the Earth-Moon system, explaining the high angular momentum characteristics of this system.
Relevant evidence
Rock samples retrieved during the Apollo moon landings showed oxygen isotope ratios nearly identical to those of Earth rocks, providing a factual basis for the giant impact hypothesis. In addition, the study shows that if the Moon has a steel core, its diameter would be no more than 25% of the Moon's radius, which is very different from the core diameter ratios of other planets. These views once again emphasize the reliability of the hypothesis that Theia may be the "mother" of the moon.
Current Challenges
Although the giant impact hypothesis is mainstream in academia, it still faces many challenges and questions. For example, did the Earth form a global magma ocean after the impact? This hypothesis has not yet been fully supported by evidence. In addition, the moon has fewer volatile elements than the earth, and the presence of water, for example, also poses a challenge to the high-temperature impact theory.
Given all the factors and perspectives mentioned above, the connection between Theia and the Moon remains an unsolved mystery in contemporary astronomy and planetary science. Can we uncover the full picture of this lost planet? This question still needs to be answered by future scientific exploration?
