The moon could have been born not inside a disk from the debris of the Earth and its progenitor Theia, but in a hot "donut" of incandescent gas that arose after their collision and evaporation of a tenth of our planet, according to an article published in JGR: Planets.
“This idea explains those unusual features of the moon that cannot be reproduced using current theories of its birth. The Moon has almost the same composition as the Earth, but still slightly different. This is the first time we have been able to explain these discrepancies,”said Sarah Stuart of the University of California at Davis (USA).
For the past 30 years, it has been generally accepted that the Moon was formed as a result of the collision of Theia, a protoplanetary body, with the "embryo" of the Earth. The collision led to the ejection of some of their rocks into space, and the Moon was formed from this matter. This idea explains well the mass of the Moon, the low iron content on it and other properties of the Earth's companion.
However, in such a collision, a significant part of the material that makes up the moon should have come from the hypothetical Theia. In its composition, it should have been different from the Earth, as most of the terrestrial planets and near-Earth asteroids differ from it. But in reality, the composition of the Earth and the Moon is very similar, up to the same proportion of isotopes of many metals and other elements.
Four years ago, Stewart and her colleagues figured out how to explain this almost 100% similarity in the composition of the Moon and Earth, proposing the Yula planet hypothesis. In accordance with it, the proto-Earth rotated so fast that it did not look like a ball, but like a flattened "whirligig", which made one revolution in just two hours and at the same time lay on its side. Theia's collision with this "whirligig" was supposed to lead to a complete mixing of their matter and the birth of the Moon, identical in composition to the young Earth.
This theory, as noted by Stewart and her colleagues, has one major drawback - for the Moon to "form" properly, it is necessary for Theia to fall to Earth at a certain angle and speed, and to have precisely calibrated dimensions and mass, which makes this scenario extremely unlikely.
All these problems, according to astronomers, can be solved if we imagine that the consequences of the collision of the Earth and Theia were much more dramatic than is commonly believed today. According to planetary scientists, their head-on collision could lead not to the formation of a flat disk from debris in the orbit of our planet, from which the Moon then arose, but a giant "donut" of evaporated rocks and metals.
“He was really huge. Its diameter was about ten times that of the Earth, and it contained about as much matter as a tenth of our planet. The rest of the Earth, thanks to the tremendous force of the collision, turned into a liquid and remained liquid for several thousand years,”adds Simon Lock, a colleague of Stewart.
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This red-hot bagel was rapidly cooling, which caused its matter to turn into liquid and "fall" to the surface of the Earth in the form of a superdense and superfast "fire rain". Part of this rain was deposited on the surface of the future moon, whose embryo appeared on the periphery of the "donut" as a result of accidental cooling and thickening of its matter.
Such an idea, as Stewart notes, well explains not only why the Moon and the Earth are very similar in composition, but also why there are almost no volatile and light elements in the bowels of the satellite of our planet, which quickly evaporated into space while “bagel surrounded the future Earth and the Moon.
In the near future, planetary scientists plan to test this idea by creating a more complete model of the newborn solar system, which takes into account all the processes that could occur on the moon during its life inside the "donut", and how it affected its matter.
