What happened to the moon?
The Moon is thought to be the result of an ancient collision between the young Earth and a Mars-sized planet. The impact caused molten rock to form a rotating torus around Earth. The moon was formed by that rock. Evidence from Apollo moon rocks shows the link between Earth and its moon.
The case is closed.
It isn't so fast. This hypothesis has always had problems. A new study can answer that question.
The moon is a primary target for many of us. When we are children, we wonder what it is. Where did it come from and why is it there? A relative might say that it was put there by a deity. You are probably not a Universe Today reader if you are interested in that area.
People in different cultures have pondered about the moon. The man was thought to be the husband of all the women. The moon was explained by a monster. Each night it eats a bit and disappears. The monster vomits it up and makes it come back. Rocks should be thrown at the Moon to frighten Alklha. The Moon goddess was thought to be a companion to the Sun god by some indigenous people in Africa. It's something to strive for in our lives.
Before science started, that was all that was left. When the British astronomer William Herschel said the moon was inhabited, he used his telescope to watch the Martians build things. At least he used a telescope. Some thought that Nazi astronauts were living in a top- secret base after landing on the Moon. It's a little more plausible.
During the Apollo missions, lunar science took a big step forward. Between 1969 and 1972 there were six Apollo missions. There was no proof of gods or supernatural beings. Lovemaking was not the cause of an eclipse.
They found a lot of scientific evidence, and one of the things they found was the amount of oxygen in the air. Oxygen isotopes in Moon rocks were similar to those in Earth rocks, according to scientists. It's possible that it's a coincidence.
The Giant Impact hypothesis has been developed by many scientists. The holes in that hypothesis have been pointed out by them. The initial finding that Earth and the Moon share the same type of radioactive material is one of the holes. They had to come from the same place. The impactor needed to have the same signature. The lighter elements were dispersed by the stellar wind. That is the reason the outer planets are gas planets. The wind couldn't move the heavy elements quickly. If Theia came from a region farther away from the Sun than Earth, it would have a different composition, and that should be reflected in the moon.
There is a lot of evidence to support the hypothesis of a giant impact. The first target in our quest to understand the sky is the moon.
There is a new study coming in. Thanks to improved simulations, it arrives at a different type of impact than the one it was previously.
The Astrophysical Journal Letters published a study on the origin of the moon. Jacob Kegerreis is a professor in the physics department at Durham University. Kegerreis is associated with the Ames research facility.
The simulations were run at higher resolutions because of the advances in computing power. The impact between Earth and Theia was different than the giant impact hypothesis would have you believe. The simulation shows that the impact caused the Moon to be created by sending a single satellite into space.
This is a huge change in understanding, like finding out that Alklha isn't real.
The researchers ran hundreds of simulations of impacts. They found that previous simulations missed important parts of massive collisions. qualitatively new behaviours emerge in a way that wasn't possible in previous studies.
The material was sent into space when the impact happened, according to the simulations. The material did not form a torus. The moon would be separated from the impactor. There is an inner remnant and an outer remnant from the impact. The outer remnant and the ejected Earth and Theia material form the Proto-Moon. The inner remnant leaves the Moon.
The animation shows the impact and the formation of the moon.
Some questions that the GIH can't answer can be answered by Kegerreis and his colleagues.
There is a roadblock to the acceptance of the GIH. An impact with another planet from a distant part of the Solar System can't produce the kind of similarity between the Earth and the Moon.
It can be explained by the new scenario. Earth material is contained in the Moon's outer layers instead of melting and mixing it with Theia material. The early Moon wasn't completely molten if the material ejected from Earth wasn't completely molten. Another obstacle the GIH has to clear is the moon's thin crust.
There is also the issue of the moon's position. The instant satellite explanation shows that it is tilted by about 5 degrees. The authors point out that an impact onto a spinning target with a different trajectory to that of Theia's can produce significant debris, including a satellite, as shown in Figure 5.
The team's simulations show that satellite creation depends on a number of factors. Both bodies have the same temperature and structure.
There is no self-consistent model that starts with a giant impact and creates debris that leads to a single Moon. The simulations have produced a single Moon. This could be the final word.
The authors write that high-resolution simulations show how a giant impact can place a satellite into a wide circle with a moon-like mass and iron content. The resulting outer layers rich in proto- Earth material and the new options opened up for the initial lunar orbit could help to explain the isotopic composition of the Moon.
The instant satellite scenario does not answer all of our questions. Scientists will continue to improve their models.
The authors say that the likelihood and potential of this and other Moon-formation scenarios will be constrained by more reliable models.
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