Why the success of the exploration of the Moon directly depends on the "battle of hypotheses" about its origin
Among the theories about the origin of Selena, there has been a serious struggle for a long time: American scientists believe that she was "knocked out" of the Earth by the blow of an ancient dead planet, and their colleagues from Russia and Israel - that there were no eschatological collisions of planets. How earthlings will explore the Moon depends on which of them is right.
At first glance, the bustle around the Earth's satellite is mysterious. On the one hand, the colonization of the Moon hardly makes sense: its area (about 1/14 of the Earth's area) is approximately equal to the area of the Earth's tropical and arctic deserts; meanwhile, even terrestrial deserts are being mastered very slowly, and the development of the moon will cost an order of magnitude more. The opinion of enthusiasts that there is helium-3 there and it is a worthy reason for the exploration of the Moon contradicts the well-known fact: an energetically favorable thermonuclear reaction has not yet been achieved even for deuterium, while the ignition of helium-3 is an order of magnitude heavier and lies outside foreseeable future of humanity. On the other hand, one power after another is planning new landings on the moon this year. The question is: why?
The correct answer to this question is simple: a scientific and resource race is "mixed" with the race of prestige. If the non-American hypotheses of the origin of the earth's satellite are correct, there is a lot of water there, and in a form of water ice that is convenient for development. In the presence of water, terrestrial crops can be grown on the lunar regolith - such experiments have already been successfully carried out. With water and food, as well as with a source of oxygen, it will be much, much easier and cheaper to study and master the Moon than in the case in which everything must be transported from Earth. We emphasize that the foundation of the base does not mean colonization. The Arctic islands and Antarctica cannot be densely populated, but there are bases there. They are needed for research, military and logistic reasons. The moon has six times less gravity than the earth. This means that it is easier from it (you need ten times less fuel) to lift the fuel and oxidizer,obtained from the same water - for example, for refueling ships flying to Mars. But to start planning lunar bases, you first need to find out: who is right? Is the Moon really dry?
Megawar: how the idea of Earth colliding with another planet was born
It is worth looking at the solar system as it was known in 1975, when the Americans Hartman and Davis formulated the theory of the Earth-Teia megacollision. In that distant year, Charon was not yet discovered and exactly two types of satellites were known in the entire solar system: those that are radically smaller than their planets (Phobos and Deimos, satellites of the giant planets), and the Moon. She was the only known satellite at that time, the mass of which was more than a percent of the mass of her planet.
The unusual nature of this satellite also demanded an unconventional theory of its origin, especially since the clumsy predecessor hypotheses, such as the separation of a piece from the Earth under the alleged action of its former rapid rotation (the hypothesis of Darwin, son of Charles Darwin), were somewhat naive and easily refuted. This and similar hypotheses poorly explained the fact that the iron core of the Moon is small in comparison with the Earth, and there is no water (as it was believed at that time).
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In fact, at that time, water in the lunar rock had already been discovered: the Apollo brought the soil to Earth, where water was found in the 60s. But it was attributed to terrestrial pollution or meteorites. Direct evidence from ion detectors that detected water near the Apollo was also attributed to terrestrial pollution. In lunar geology, a phenomenon that is more often attributed to the humanities was triggered - scientists rejected empirical facts, since they did not fit with the then existing theories of the origin of Selena: in all of them, it first melted, that is, it had to lose water. Science of that time assumed only one variant of water hitting the moon - with comets. But in cometary water, the ratio of deuterium to hydrogen is different, and in water found on the Moon by the Americans, the ratio of these hydrogen isotopes was the same as on Earth. The theory of that time did not allow this,why everything was attributed to "earth pollution", and Selena was declared completely waterless.
However, other features of the lunar soil by terrestrial pollution could not be explained. It is about a lower content of titanium and other relatively heavy elements.
Collision of the Earth with another planet.
It was then, in 1975, that the mega-impact hypothesis (mega-impact) was born in the USA. According to it, the ancient planet Theia 4.5 billion years ago collided with the Earth and a super-powerful impact threw a large amount of material from both planets into space. The moon formed from the debris over time. The earthly satellite was obtained not "primary" (as, for example, the satellites of Jupiter), but "secondary", arising from the collision of large celestial bodies. The question was removed as to why the mass of Selena is so large in comparison with the mass of the Earth itself - much more than that of the satellites of other planets of the solar system.
The Mega Impact also easily explained why there were few heavy elements on the Moon (which was true) and no water at all (which after the Apollo flights was stubborn ignorance of the facts). The upper layers of the Earth contain few heavy elements - most of them sank down into the core and lower layers of magma. When the planets collided, the debris should have flared up to thousands of degrees. Any water from them would evaporate and fly into space. When the cooled debris formed the moon, they should have been completely dry by now.
It seems someone missed
The hypothesis looked just fine for three whole years. But already in 1978, Charon, a satellite of Pluto, was discovered. If the Moon is 80 times less massive than the Earth, then Charon is only nine times lighter than Pluto. It turned out that there is nothing unique about the appearance of the moon. A natural question arose: how is this possible, since the collision of large planets like Theia and the Earth must be a rare event?
An artist's view of Charon from the surface of Pluto.
Even more inconvenient was the analysis of lunar rocks in laboratories and the first data on meteorites of alien origin. It turned out that only the Moon is isotopically indistinguishable from the Earth, and all other planets of the solar system are clearly different. How did this happen if Selena supposedly contains the substance of another planet - the hypothetical ancient Theia?
To explain the contradiction, the hypothesis of the mega-shock was modified: the place of birth of Teia was considered … the Earth's orbit, therefore the isotopic composition of both planets is the same. Allegedly, two planets formed on it at once, which then collided. It was not clear why two planets appeared on the earth's orbit, and one at a time on the orbits of other planets of the system.
Geologists also added problems. A legitimate question arose: if the mega collision of two planets heated the Earth and its debris, where did the water come from on the planet? By all accounts, it should have evaporated. The theory of the mega-impact has already become extremely popular, they did not want to abandon it, so the idea was put forward that water appeared on Earth later - it was brought by comets that fell on the planet for billions of years. But it was soon discovered that the ratio of isotopes of hydrogen and oxygen in cometary water is very different from the same ratio in terrestrial water. Water from asteroids is more similar, but there is very little of it on them, that is, they cannot be the source of the Earth's oceans.
Finally, in the 21st century, traces of water began to be found on the moon. And when the proponents of the mega-shock hypothesis suggested that comets brought this water, Dutch geologists showed that lunar rocks could not have formed in their present form without the presence of water from the very beginning of the formation of the satellite. The situation was aggravated by Russian astronomers: in their opinion, a typical collision of a comet with the Moon leads to the departure of more than 95% of the water back into space.
Best of all, the situation was reflected in the article of 2013 with the telling headline "Impact theory is exhausted".
How the asteroid hammer built the moon
In 2007, the work of the famous physicist N. Gorkavy "The Formation of the Moon and Binary Asteroids" was published, which showed for the first time that the mechanism of the formation of the Moon is not unique - on the contrary, it gave rise to a huge number of satellites in the solar system. Only these satellites were formed mainly in asteroids, and not in more massive planets.
The scenario for the appearance of both asteroid satellites and the Moon is simple. The very first collisions with asteroids 10-1000 kilometers in size form a ring of ejected debris around the planet, the speed of which is higher than the first cosmic one (that is, they cannot quickly fall back). Subsequent asteroid strikes rapidly increase the mass of the disk - its debris "intercepts" new debris flying off the planet. Those that flew in the direction opposite to the direction of rotation of the disk and the planet, from the collision with the debris of the disk, lose their speed and fall back to the planet. Those that fly in the same direction as the disk and planet rotate - join the disk. The more its mass, the more debris knocked out by new asteroids, it can capture. From more and more collisions, old debris in the disk lose energy and speed, it becomes easier for them to "stick together" upon impact,without scattering after collision. So a large satellite begins to form in the disk.
In such a scenario, neither the Earth nor the knocked-out debris heat up to thousands of degrees, that is, the earth's water does not boil away either in the earth's oceans or as part of the moon. And the isotopes in their solid rocks coincide, because Selene, it turns out, arose mainly from the earth's debris.
It also becomes easy to understand the origin of the lunar seas on the part of the Moon facing the Earth (about 3-4 billion years ago, lava poured onto the surface of the Moon and, frozen, formed dark seas covering 16% of the lunar surface area and located on the visible side of the Moon). If the Moon "intercepts" all the debris knocked out by asteroids from the Earth, then it should "catch" them with the side facing the Earth. Therefore, there are much fewer lunar seas on the shadow side of the satellite.
As is often the case with hypotheses in our time, several scientific groups can make the same discovery, because there are many articles in peer-reviewed journals, and not all scientists have enough time to read them. Gorkavy's conclusions were "rediscovered" in 2014 by a Moscow group of astronomers, and in 2015 by an Israeli one. So far, this hypothesis is not accepted only in the United States, however, it is only a matter of time. The contradictions of the mega-impact hypothesis are insoluble, while the new one does not yet show any contradictions with the observed reality.
How the new theory will change the practice of studying and exploring the moon
If the Moon was formed from terrestrial material, there must be light elements on it. Water from the surface soon evaporated, but there is no Sun in the circumpolar zones (especially in craters). Radar data support this hypothesis. This means that events that seem to be billions of years ago are of vital importance today. If lunar water was a product of comets, it would be scarce and it would hardly be preserved in the form of noticeable amounts of pure ice.
Entrances to lava tubes, inside of which there may be a lot of water ice.
What is important, in addition to circumpolar craters, there are other places on the planet where the presence of light elements is possible - lava tubes. In conditions of low lunar gravity, such volcanic caves have a diameter of up to hundreds of meters, and their length is measured in kilometers. A layer of soil from 10 meters completely protects the interior of the caves from cosmic radiation, and the temperature in them is always stable. American researchers suggest that there, as in a number of the Earth's lava tubes, there may be pure water ice. There are many entrances to the lunar lava tubes (pictured above). There is no better place for a lunar research base.
Crater in the Sea of Tranquility (Mare Tranquillitatis).
In the light of new data, it is necessary to explore the Moon not at low latitudes, as the Americans did in the 60-70s, but in completely different places - closer to the poles. It is there, by the way, as it is easy to be convinced, that Indians and other new participants in the lunar race are sending their vehicles. In any attempt to create a lunar base, water ice will be a valuable resource. In addition, in the near-polar zone of the Moon, sunlight shines in some places for more than 95% of the duration of the year. This will further simplify the basing. It is clear that no one will declare the pieces of the satellite as the property of the terrestrial state, but, as with the Arctic bases, the one who is the first to gain a foothold in a favorable place will have great advantages in studying the moon.
So, the American theory of the formation of the Moon during an interplanetary collision claims that Selena is a dry piece of stone, where there is little water and it is only alluvial. The Russian and later Israeli postulate that the Earth's satellite arose from many impacts of small asteroids and therefore is rich in water. The one who is the first to find out which of the theories is correct will get a big head start in the development of lunar water. It is she who will become a key resource, without which neither the lunar base in particular, nor a detailed study of the Moon in general is possible.