The absence of "seas" and the abundance of mountains on the far side of the Moon may be the result of the fall of another satellite of the Earth on it, according to American planetary scientists. Such a satellite may well have formed along with the Moon as a result of the collision of the young Earth with a planet the size of Mars. Its slow fall to the moon led to the fact that one half of it was covered with an uneven layer of rock tens of kilometers thick
Over billions of years, tidal forces have equalized the times during which the Moon makes one revolution around its axis and one revolution around the Earth. For this reason, the Moon always faces the Earth with one and the same side, and we can say that before the beginning of the era of space flights, humanity had a very "one-sided" idea of our closest celestial neighbor. The first images of the far side of the Moon were transmitted to Earth by the Soviet automatic station " Luna-3 " in 1959. Already on them it was clear that the two hemispheres of the moon are completely different from each other. The surface of the side invisible from Earth is covered with many high mountains and strongly cratered, while on the side facing us there are much more plains and fewer mountain ranges.
Visible (A) and invisible (B) from the Earth hemisphere of the Moon. The nature of their relief is very different: on the reverse side there are much more high mountain ranges and craters // John D. Dix, Astronomy: Journey to the Cosmic Frontier
Photo: Credit unknown / paranormal-news.ru
Along with the fundamental question of the origin of the Moon as such, the difference in the relief of its hemispheres to this day remains one of the unsolved problems of modern planetary science.
It excites the minds of people and even gives rise to completely fantastic hypotheses, according to one of which the Moon was recently united with the Earth, and its asymmetry is a "scar" from separation.
The most widely accepted theory of the moon's origins today is the so-called Big Splash or Giant Impact. According to her, in the early stages of the formation of the solar system, the young Earth collided with a body comparable in size to Mars. This cosmic catastrophe generated a lot of debris in near-earth orbit, from part of which the Moon was formed, and part of which later fell back to Earth.
Planetologists from the University of California (Santa Cruz, USA) Martin Jutsy and Eric Asfog proposed an idea that, within the framework of this theory, is able to explain the difference between the releft of the visible and far sides of the Moon. In their opinion, the "Giant Collision" could have spawned not only the Moon itself, but also an additional satellite of a smaller size. Remaining initially in the same orbit as the Moon, it eventually fell to its older sister, covering one of its sides with its substance, forming an additional layer of rocks several tens of kilometers thick. Their work is published in the journal Nature.
Jutsa and Asfog arrived at such inputs on the basis of computer simulations carried out on a supercomputer at the University of California "Pleiades". Even earlier, modeling the collision itself, Erik Asfog discovered that after it, from the same protolunar disk, a small additional satellite with a third size and a mass of one-thirtieth lunar could well have formed. Although, in order to survive in orbit long enough, he had to get into one of the so-called Trojan points of the lunar orbit - the points where the forces of attraction from the Earth and the Moon are balanced. This allows matter to remain in them for tens of millions of years. During this time, the moon itself has time to cool down, and its surface hardens.
Ultimately, due to the gradual removal of the Moon from the Earth, the position of the additional satellite in orbit turned out to be unstable and that "slowly" (by cosmic standards, of course, at a speed of about 2.5 km / s) collided with the Moon. What happened could not even be called impacts in the usual sense of the word - the collision that took place did not lead to the formation of a crater and the melting of the lunar rock. Instead of this, most of the falling body simply fell on the moon, and covered one half of it with a new thick layer of rock.
The final picture of the lunar relief, obtained as a result of the carried out modeling, turned out to be very similar to that which is actually observed today on the far side of the Moon.
Promotional video:
The collision of the Moon with a small satellite, followed by a "fallout" on the lunar surface, which formed a difference in the relief of its two hemispheres // Martin Jutzi and Erik Asphaug
Photo: Martin Jutzi and Erik Asphaug / gazeta.ru
In addition, the idea of American scientists helps explain the chemical composition of the surface of the visible side of the moon. The crust of this half of the moon is very rich in potassium, rare earth elements and phosphorus. It is assumed that these elements (as well as uranium and thorium) were originally components of molten magma, now solidified under a thick layer of the lunar crust. The slow collision of the Moon with a smaller body, in fact, pushed the rock, enriched in these substances, towards the opposite hemisphere of the collision. This led to the observed distribution of chemical elements on the visible surface of the Earth's satellite.
Of course, the research carried out does not completely cover either the problem of the origin of the Moon or the appearance of asymmetry in the surface of its hemispheres. But it is a step forward in our understanding of the possible paths for the development of the young solar system in general and our planet in particular.
“The fact that the visible side of the moon is so unlike the opposite has been a mystery since the beginning of the space age, although only in second place - after the mystery of the origin of the moon itself.
The elegance of Eric's work lies in the fact that it proposes to solve both mysteries at the same time: it is possible that the giant collision that formed the Moon also gave rise to several smaller bodies, one of which then fell on it and led to the observed dichotomy"
- this is how Professor Francis Nimmo, a planetary scientist from the same University of California, commented on the work of his colleagues. Last year, with Ian Garrick-Bethel, he published a paper in Science defending another way of solving the same problem. According to Nimmo, tidal forces are more likely to be responsible for the formation of the dichotomy of the lunar relief than some event of shock nature.
“Today we do not have enough information to make a choice between the two proposed solutions. Which of the two hypotheses will be more correct will become clear after space missions bring us additional experimental data and possibly even rock samples,”added Nimmo.