Before the birth of the Moon, our planet rotated on its side, like Uranus, and only a collision with the "grandmother" of the Moon Theia and the formation of a satellite of the Earth forced her to change habits and begin to rotate in a "normal" way, planetary scientists say in an article published in the journal Nature.
“Our work shows that the Earth's axis of rotation could change its position in several ways at once. We thought that the Earth became what it is as a result of a collision with Theia at an unusual angle, but it seems that the axis of our planet was tilted much later as a result of complex gravitational interactions with the Moon and the Sun,”says Matija Chuk. Cuk from the SETI Institute in Mountain View (USA).
Space whirligig
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 release of the matter of Theia and the proto-Earth into space, from this matter the Moon was formed. The theory of the collision of the proto-Earth with a large celestial body explains well the mass of the Moon, the low iron content on it, and other parameters.
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 celestial bodies of the inner region of the solar system, including the terrestrial planets and asteroids, differ from it. But in fact, 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, Chuck and his colleague Sarah Stewart figured out how to explain this almost one hundred percent similarity by proposing the Yule planet hypothesis. In accordance with it, the proto-Earth rotated so quickly that it looked not like a ball, but like a flattened whirligig, which made one revolution in just two hours. 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.
The problem, as the authors themselves later discovered, is that such a hypothesis does not explain why the moon's axis of rotation is tilted five degrees in relation to the orbital plane along which the earth revolves around the sun.
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Further study of this issue showed that in the past, when the Moon was gradually moving away from the Earth, tidal forces should have strongly displaced the axis of our planet, which put the idea of a "yula planet" into question. In addition, scientists did not have a clear explanation of how the Earth could slow down its rotation on its axis to its current values.
Space break dance
Chuck and his colleagues found a way to save their theory by literally turning the Earth on its side. According to them, the newborn Earth could revolve around the Sun not in an upright position, but lying on its side, like Uranus, whose axis of rotation is rotated by almost 90 degrees.
As shown by computer modeling of the collision of the Earth-"Yula" and Teii, the most plausible results were obtained, paradoxically, in those cases when the Earth initially lay on its side, and the Moon revolved around it actually along the equator, which at that time passed through those points, which now occupy the North and South Poles.
Such a perpendicular arrangement of the orbits of the Moon (around our planet) and the Earth (around the Sun) led to the appearance of extremely interesting gravitational interactions between the star and the two planets.
At the first stage of these interactions, the Moon acted as a kind of "gravitational rope", which was pulled between the Earth and the Sun. As a result, the speed of rotation of our planet quickly dropped to almost modern values in a moment by cosmic standards - several million years.
When the rotation of the Earth's whirligig slowed down to a certain speed, the Moon, with the support of the Sun, began to gradually raise the Earth's orbit, bringing it closer to the present angle of inclination of 21 degrees. Together with the Earth, the Moon itself moved, dropping to its present orbit, inclined to the plane of the Earth's orbit by six degrees.
According to Chuk, such an explanation of the birth of the Moon is important not only for understanding the history of our planet, but also for assessing the possibility of the existence of life outside the solar system. The existence of different tilts of the planet's axis, according to the planetary scientist, increases our chances of detecting life, especially in those exomers that have large satellites like the moon.