Among the many natural satellites in the solar system, the moon seems very different. Its mass is about 1/81 of the earth and its diameter reaches about 27% of that of the earth. For rocky planets like the earth, natural satellites like the moon are too big, and this also strongly implies that the moon is likely to have a unique origin.
In the past days, people have proposed various hypotheses about the origin of the moon, and one of the theory, called the "Great Impact Hypothesis", was finally widely recognized by the scientific community. The hypothesis believes that the moon was formed in a "major impact event" about 4.5 billion years ago, in which a planet about the size of Mars hit the earth.
This planet is called " Theia ". After a violent collision with the earth, most of the matter that constitutes it is swallowed by the earth. Under the constraints of the earth's gravity, some of the "fragments" produced by this impact revolve around the earth while accreting to each other and eventually forming the moon.
Then the question arises. How long has the moon been formed in the above process? Usually we think that it will take a long time to form a celestial body as big as the moon. In fact, astronomers generally believe that it will take at least thousands of years.
However, a research team from Durham University gave an incredible answer. On October 4, 2022, the team published a paper in the Journal of Astrophysics Express, saying that their new research shows that the moon may have taken only a few hours to form.
This research work can actually be summarized simply as: using supercomputers to simulate a "big impact event", perform high-precision simulation of collisions at different angles, rotation and speeds, and find the one that is most in line with the actual situation.
Researchers said that if you use toy building blocks to simulate the situation that a car may encounter during a collision, then if you use only a few dozen building blocks, the model will easily break from the connection between the building blocks, which will be very different from the actual situation. However, when building a model car of the same size, if you use tens of thousands of building blocks, the simulated situation will be much closer to the real situation.
Generally speaking, only 100,000 to 1 million "building blocks" used to simulate celestial bodies impacting will be used. However, in order to make the simulated "big impact event" closer to the real situation, as many as 100,000 "building blocks" were used in this study, which undoubtedly makes the simulation process extremely complicated.
It is precisely because of this that the researchers used the school's supercomputer, "Cosmology Machine" (COSMA). After a lot of simulations, the researchers found the one that best suits the actual situation, as follows:
After the impact, "Theia" was almost "broken to pieces", and the earth was also severely damaged. In the violent impact, a large amount of matter was thrown out, but these matter did not splash around, but were quickly concentrated in two areas. For the sake of description, we might as well call the area with more matter "region 1" and the other "region 2".
"Region 1" has relatively large mass, and the gravity it generates is of course not to be underestimated. It can be seen that due to the relative movement of of "Region 1" and the effect of gravity, the movement trajectory and speed of "Region 2" have undergone significant changes, and it looks like it was directly "thrown" by "Region 1".
In fact, this can be seen as a powerful gravitational boost. After "zoning" "region 2", "zoning 1" cannot escape the control of the earth's gravity. It is quickly recaptured by the earth, and "zoning 2" has a high enough speed with the help of "zoning 1" and smoothly enters the orbit around the earth.
In the following time, most of the residual material in the space near the earth fell into the earth along a spiral curve, and the matter in "region 2" quickly reached hydrostatic equilibrium , thus forming a new planet. Yes, this planet is the moon we see now, and according to the simulation of supercomputers, the process only took a few hours.
Based on this we can clearly see that the reason why the formation time of the moon is so short that it is incredibly short is actually because the moon was directly formed in the "major impact event" and did not experience the slow and gradual accretion process previously speculated. Of course, this is just a speculation. For us humans, there are still many puzzles on the moon waiting for us to explore.
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(Some of the pictures in this article are from the Internet. If there is any infringement, please contact the author to delete it)
Reference materials:
J. A. Kegerreis et, al. Immediate Origin of the Moon as a Post-impact Satellite. The Astrophysical Journal Letters, Volume 937, Number 2, Published 2022 October 4
