According to the current scientific state, the Moon was formed from Earth rocks as a result of a collision with another celestial body. However, a research group has highlighted that there are several things wrong with the theory.
According to the giant impact hypothesis, billions of years ago, something the size of Mars slammed into Earth, ejecting a mass of rock into space that eventually coalesced to form the Moon. There’s just one problem. According to a new analysis by planetary scientist Paolo Susi of the Experimental Planetology Group at ETH Zurich in Switzerland, we have absolutely no clear evidence that such a giant impact ever happened.
“Rocks from the Earth's mantle and the Moon cannot be distinguished by any isotopic ratio that traces the origin of materials in the solar system,” Sosi said in his report. Science AlertL. “Because the isotopes of these elements vary greatly between planetary materials, if there are traces of impact, we would expect to see small differences in isotope ratios. […] In the event of a collision, the two celestial bodies should be completely mixed together.”
This does not clearly deny that the giant impact broke it, but it reopens the question of the Moon's birth. The evidence for this is arXiv Available on a pre-print server and currently appearing in Geochemistry 2024, it is based on a critical review of all relevant geophysical and geochemical evidence to date.
If there was no giant collision, where did the moon come from?
Al-Soussi claims that the Earth and its companion simply formed from the same material, so there is no need to introduce a hypothetical third body. The Earth and the Moon are unique in the solar system. It is the only system in which there are two large spherical bodies with different cores. The Moon is not much smaller than Mercury, and if it were floating on its own, it would be considered a planet in its own right.
The Moon is also thought to have played an important role in the evolution of life. It helps stabilize the Earth's rotation and creates tides that help the oceans circulate. The Earth would be very different without the mass of rock orbiting the Earth.
We cannot rule out the giant impact hypothesis either.
In the early days of the solar system, about 4.5 billion years ago, things were a lot more chaotic. Lots of rocks were flying around freely, as evidenced by the craters left behind by the planets and moons that remain. It’s entirely possible that the young Earth collided with something large enough to create the debris cloud that forms the Moon.
The problem, Sosi and his team concluded after examining the available evidence, is that the Earth and the Moon are very similar. The ratio of isotopes of elements on Earth and the Moon—different forms of the same atom with different numbers of neutrons in the nucleus—is the same. Initially, this match was only observed for oxygen isotopes, but more recently for chromium and titanium as well.
“Furthermore, since the isotopes of these elements vary greatly between planetary materials, if they were traces of an impact, we would expect to see small differences in their isotope ratios. However, no such differences have been observed between the Earth and the Moon. This has subsequently been shown to be true for many other elements (e.g. iron, calcium, molybdenum, etc.), so it is astronomically unlikely that they could have arisen by chance.
How were the Earth and Moon born?
According to a new study, the Earth and Moon are roughly the same age, or very close to each other, about 4.5 billion years ago. Together, the evidence suggests that the two bodies formed from the same cloud of material.
That doesn't mean there couldn't have been an impact. According to one model, the collision crushed the entirety of what the nascent Earth looked like, creating a doughnut-sized mass of material that coalesced into two celestial bodies, the Earth and the Moon.
But giant impact models often predict small differences in the isotope ratios of the Earth and Moon. These differences simply do not exist according to the existing data, which means that while the impact cannot be ruled out, we must rule out models that produce results inconsistent with the actual geochemical data.
It could have been practically anything.
We simply don’t know how the Earth and Moon came together from a pool of interstellar dust 4.5 billion years ago. One way to investigate further is to look at what’s inside the Moon, and that’s what Sosi and his colleagues are working on.
“The chemical and isotopic evidence is now strong enough to begin to question the fundamental mechanisms of Moon formation,” said Sosi. “We are also excited to see how geophysical, geochemical, and dynamical constraints interrelate to provide a new, comprehensive picture of Moon formation. We are able to communicate across disciplines on common problems, which will ultimately help us solve this mystery.”
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