US, WASHINGTON (ORDO NEWS) — The planets of the solar system formed in relatively similar ways – from a protoplanetary disk, similar to which astronomers find in other stars today. During the formation of a planet in one or another orbit, it acts like a vacuum cleaner there: it attracts all planetesimals (small protoplanetary bodies).
Sooner or later, almost all of them should fall on the planet. An exception may be only small bodies, similar in size to Deimos, but the Moon is so large that it cannot be built from such small “crumbs”.
A natural question arises: how did our companion come about (since the word “moon” is feminine)? From the foregoing, it is obvious: this could only happen after the formation of the Earth and only due to some powerful external forces – pieces of the Earth themselves did not come off and did not fly into the sky (although in the 19th century there was such a somewhat naive hypothesis).
It is enough to look at the Moon with good binoculars, so that the idea of the source of these mysterious external forces comes to mind by itself. The satellite is covered with a mass of craters – traces of the fall of asteroids.
Maybe a bunch of asteroids flew into Earth orbit, which then gradually collided with each other, their wreckage created a kind of Saturn’s rings, and then lost speed and formed the moon due to weak collisions? Such a hypothesis was put forward in 1975 by the Soviet astronomer Eugenia Ruskol, but, alas, did not survive analyzes of the lunar soil.
The fact is that the samples of Apollo and the Soviet Moon-24 showed that the ratio of the isotopes of different elements in the lunar and terrestrial soil is almost indistinguishable.
This means that the Earth’s satellite could not have formed in the main from asteroids that arrived from other parts of the solar system. Indeed, different sections of the protoplanetary disk have a different ratio of isotopes of certain elements. This can be easily traced from analyzes of Martian soil or meteorites that are found on Earth.
In addition, in the material of the planets, heavy elements easily go down to the core, there are few of them in the mantle. The lunar surface showed an “earthly” deficit of heavy elements – for example, iron. But in asteroids, heavy elements do not sink anywhere – they are too low-mass for this.
It went without saying that the moon was supposed to form mainly from earthly material – but how?
American scientists William Hartman and Donald Davis in the same 1975 proposed an extremely intriguing mega-impact hypothesis. On it, the planet Theia collided with the ancient proto-Earth about 4.5 billion years ago. The impact threw many fragments of our planet into the Earth’s orbit, and they were seriously heated by the shock event, whose energy, according to calculations, should have been estimated at least in trillions of megatons.
There were two important consequences of this hypothesis. First, the Earth had to lose its primary ocean – that literally boiled away after an impact. Secondly, the Moon, whose components after a huge impact were warmed up even more than the Earth’s (up to thousands of degrees), was supposed to lose all the water in general. And equally – all light elements.
Earth scientists strike back at Teya
For twenty-five years, it seemed that everything was clear with the formation of the moon. It was not in vain that we used the word: we found water in the same lunar soil delivered by the Apollo and Luna 24, which is not particularly compatible with the heating of the components of the Earth’s satellite from an explosion of trillions of megatons.
But the question was solved simply: the US lunar program was developed in a hurry, so the containers for soil from the satellite there were not very successful: they were leaky (regolith spilled out of them during transportation). The water in them was written off to pollute the samples already on Earth. They also wrote off the data of the Apollo ion detectors, which also showed water in the lunar soil.
Soviet samples were in normal containers, so there’s nothing you can do here. But another thing helped: in the West, no one noticed the corresponding Soviet work .
Nevertheless, problems arose – and it was precisely the strength of the mega impact, the calculation derived at least trillions of megatons. Already in the XXI century, a series of observations from the orbit of the moon showed that in the circumpolar craters of the satellite there is a very thick layer of water ice. According to the latest estimates for 2019, its there are 100 billion tons.
It should be noted that we are talking only about what is on the surface, in the craters. Water ice in huge lava tubes (moon caves with a diameter of up to kilometers) cannot be estimated from orbit, and its amount can be much larger.
Of course, this is difficult to combine with the hypothesis of “dry sublimation” as a means of obtaining lunar material from the earth, knocked out by Theia. When heated, water evaporates quickly and easily, and the typical speed of its molecule is so great that debris simply can not hold it with its gravity.
Objections were also received from Earth explorers. The blow of the force necessary for the formation of the Moon definitely had to not only evaporate the oceans, but also arrange lava seas on Earth for some time: to melt the upper layers of the planet. However, geologists unequivocally argue that there are no traces of lava seas on our planet – not like the global lava ocean, but even local ones.
To close the issue of lunar water, the idea was proposed that it was brought there by comets from the outer regions of the solar system. True, it turns out that comets were supposed to fly to the moon by conveyor: according to Russian scientists, at least 95% of the material when a comet hits our satellite should be thrown back into space.
It turns out that comets brought trillions of tons of water to the Earth’s satellite at least — a very strange result, given that the gravity of a nearby Earth should intercept most of the comets traveling through this region of the system.
In 2007, the first alternative explanation for the problems of the mega-impact hypothesis appeared. Nikolai Gorkavy published the article “The Formation of the Moon and Double Asteroids”, where he showed that a completely different mechanism for the birth of our satellite is possible.
He called his model “multi-impact” and suggested that it could be a typical mechanism for the formation of large satellites – not only the Earth’s Moon, but also Charon at Pluto, and even double asteroids.
The essence of the multi-impact model is in the assumption that the Earth’s satellite was built not by one giant collision, but by many smaller ones. A large enough asteroid falling to Earth definitely knocks debris out of it.
But since the collision energy is low, no lava seas are formed on Earth. And the discarded fragments do not completely melt: their central parts may not even reach the boiling point of water.
After falling into low Earth orbit, such fragments had two options for further fate. The fact is that at the early stage of the history of our planet, a low-mass protosatellite disk should rotate around it, and in the same direction as our planet.
After the fall of a large asteroid to Earth, those earth debris that were thrown in the direction of rotation of the planet, as it were, “added up” with this disk. But those fragments that flew out of the atmosphere “against the wool” lost their energy from a collision with a protosatellite disk. An object in orbit that loses its energy inevitably falls – that is, such debris has returned to our planet.
And “defectors” could eventually seriously raise the mass of the protosatellite disk – up to 1% of the mass of the entire Earth or even higher.
Stop-stop, the reader will say. But what about commonplace logic? If we shoot into space from an electromagnetic accelerator, the body will either fly away from the vicinity of the Earth, or eventually fall to its surface.
Say, this is exactly what will happen to all artificial satellites of the Earth: over time, they will brake on the dust of near-Earth space and still fall on the planet. How does it suddenly turn out that the debris resulting from the collision of the Earth with ancient asteroids “hovered” in the sky for 4.5 billion years, folding into the moon?
Here lies the main merit of the multiimpact model. Indeed, a fragment of the Earth itself cannot stay in orbit for billions of years. But when Gorky calculated the interaction of this fragment with an ancient simple satellite disk, it turned out that the situation was changing radically.
Although the ancient disk was not massive, it possessed stable orbits of its bodies. When the wreckage knocked out of the Earth by another asteroid and flying “in the hair” caught up with any of the bodies of the protosatellite disk, they collided with it and gave it part of their energy.
As a result, the forming Moon from the protosatellite disk could not fall to the Earth: it was constantly “thrown” slightly by the blows of new debris. As a result, part of the “pushing” earth debris fell on the planet, and part – on the proto-moon, adding mass to it. Over time, in this scenario, the Moon should begin to move away from the planet, as we observe in practice.
The total number of asteroids needed to form a lunar-sized body from debris knocked out of the Earth seems rather large – there could be millions of them. And we are talking about bodies with a diameter of 10 to 1000 kilometers.
Now, such quantities of these bodies do not fly through the system, but from the large number of ancient craters on the far side of the moon it is obvious that they were three to four billion years ago. Conclusion: formally, everything converges.
Gorky’s hypothesis also had drawbacks: it is not very popular in the USA due to the fact that, like everywhere, national scientific schools are more inclined to “homegrown” scientific theories than to ideas from abroad.
In addition, the author was published in a Russian-language scientific journal, which further complicated the familiarity with his concept of non-Russian speakers. Therefore, American researchers still adhere to the mega-impact theory, although they admit that the origin of lunar water in it is somewhat mysterious
Japanese Observations: A Point in the Moon Debate?
The authors of the new work in Science Advances studied the spectrometer data of the Japanese artificial moon “Kaguya”, which worked back in 2007-2009. They turned to the side of his observations that had not previously been put into scientific circulation, namely, to the registration of carbon ions by him. It turned out that, on average, 50 thousand of such ions per second fly out from one square centimeter of the lunar surface.
This is quite a lot: according to calculations, more than the solar wind stream and the micrometeoroid stream can supply to the Moon. In addition, over the basaltic regions of the lunar seas, the flux of carbon ions is greater than over the regolith, because basalt poured out of the lunar mantle, that is, it cannot be rich in an element that was not originally on the moon.
All this means that carbon and other light elements inevitably should have been on the moon since its inception and can in no way be attributed to the “contribution” with comets and other bodies from the outer regions of the solar system.
In theory, this closes the question. The large amount of carbon on the moon clearly says that it could not be “dry” and devoid of light elements, as the mega-impact hypothesis claims. These data are also useful from a practical point of view: most likely, in the lava tubes they will find not only water, but also dry ice (solid CO2).
Oddly enough, in a number of cases it is a valuable resource from which methane can be obtained – a promising rocket fuel, the first rocket engine for which in 2019 was already tested by the flight of the SpaceX experimental stand.
Until now, it was known that there was only water ice on the moon. In theory, it can also be decomposed into oxygen and hydrogen, and the latter is not bad fuel. Alas, in practice its use outside the Earth is problematic: hydrogen molecules are so small that in vacuum even the best tanks for several months of storage begin to lose it in large quantities.
Liquefied methane is much easier to keep in tanks: it can be stored there for years. Therefore, when using the Moon as a “refueling site” on the way to Mars, it is potentially much more interesting to get methane from CO2 and water decomposition products than to extract lunar hydrogen from local water.
However, while this is a matter of perspective. The immediate results of the Kagui observations are not difficult to predict: now supporters of the mega-impact theory will hastily search for some explanation and modify their hypothesis to explain how exactly the rocks molten during the impact of the hypothetical Teija were able to hold light elements.
Scientists are inventive people, so we believe that they will succeed, the megaimpact parameters will be modified again and somehow adjusted to the newly found facts. Nevertheless, in a strategic sense, their efforts to save mega-impact theory are doomed.
The probability of such an event as the collision of two planets is a huge number of times lower than the probability of the fall of millions of asteroids onto the ancient Earth.
The first event is so difficult to implement that so far no one has even given reasonable estimates of its probability. Asteroid bombardment – as it is easy to see from the relief of the same Moon and other satellites of our system – is more than usual. This means that this is a natural process, more appropriate to Occam’s razor.
It follows that the theory of multi-impact moon formation will win, although it is possible that this will happen only after the current generation of mega-impact supporters retires.
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