The speed at which the moon is moving away from the earth. Can the moon fly away from the Earth? Losing the Moon won't turn Earth into Venus

Origin of the Moon. It was a long time ago. So long ago that it’s hard to even imagine. To determine the number of years that have passed, you would have to write a number with nine zeros.

At that time, the Moon and Earth were one. The huge molten ball made one revolution around its axis in just four hours. The centrifugal force at the equator and the tides that the Sun caused in this ball elongated in its direction came into resonance with the ball’s own vibration and tore off a piece from it, which eventually became the Moon.

At the site of this detachment, the greatest depression on Earth has remained to this day, now occupied by the Pacific Ocean.

This is what the famous English astronomer believed George Darwin(1845–1912), son Charles Darwin(1809–1882). And, despite the fact that his hypothesis about the origin of the Moon is not now generally accepted, observations and calculations show that two billion years ago our natural satellite was at a very close distance from the Earth.

But our planet and the Moon are 4.5 billion years old (this is also evidenced by the age of the oldest lunar rocks). If the Earth and Moon had appeared together at that moment, they would have moved significantly further away from each other than they do now.

What happened during the first half of their existence? Where was the moon? Maybe they formed together, but earlier the Moon was moving away from our planet less intensely than it is now? Or maybe somewhere it revolved around the Sun as a planet, and then, due to some circumstances, was captured into low-Earth orbit and became a satellite of the Earth?

These questions, together with Darwin’s version, reflect three hypotheses of the origin of the Moon, which have been quite popular in science for a long time: 1) separation from the Earth, 2) its formation at the same time as our planet, and 3) capture of a ready-made satellite.

In 1975, another, catastrophic hypothesis appeared, which connects the origin of the Moon with the collision of the Earth with a large cosmic body comparable in mass to the planet Mars.

Let us briefly dwell on these hypotheses and analyze them, taking into account the main physical characteristics of our natural satellite. Along with its size and mass, the most important parameter of a planet is its average density, which allows us to determine its chemical composition. For the Moon it is 3.3 g/cm 3 (for the Earth 5.5 g/cm 3). The lunar density is close to the density of the Earth mantle, lithosphere The Earth, its rocky shell, which occupies 70% of the planet’s mass - from the iron-nickel core (half the Earth’s radius) to the surface. As for the Moon, it has a very small iron-nickel core, only 2–3% by mass (Fig. 2).

1) It would seem that if the lunar substance is similar to the substance of the earth’s mantle, then this is a convincing argument that the Moon at one time broke away from the Earth. Based on this, the hypothesis of the separation of the Moon from the Earth (jokingly called “daughter”) was very popular at one time and was generally accepted at the beginning of the twentieth century.

In favor of this version of the origin of the Moon, a similar ratio of oxygen isotopes 16 O, 17 O and 18 O was obtained relatively recently in lunar rocks and rocks of the Earth’s mantle. However, in addition to the similarity of the lunar substance with the substance of the earth's mantle, there are also significant differences.

Indeed, the so-called volatile (low-melting) and siderophilic There are significantly fewer elements in lunar rocks than in terrestrial rocks. In addition, for centrifugal force and tide to tear off a piece of the globe, a period of its rotation of at least 2 hours is required so that the half-period of rotation would resonate with the period of natural oscillations of this ball (about an hour), and the mass of the torn piece, as calculations show, should make up 10–20% of the Earth's mass.

In fact, the mass of the Moon is 81 times less than the mass of the Earth, and the mass of the mantle material in the volume of the Pacific Trench would be only a small fraction of the mass of the Moon. In addition, the age of the Pacific Ocean is estimated to be about 500 million years, while the age of the Moon and Earth is 4.5 billion years. Thus, the hypothesis of the separation of the Moon from the Earth does not withstand the strict criticism of specialists.

2) If the Moon and Earth were simultaneously formed from the same ring protoplanetary clouds (jokingly - a “sister” hypothesis), this easily explains the identity of the oxygen-isotopic ratio of their substance, but does not agree with its difference in density and with a deficiency of iron and siderophile and volatile elements.

One of the authors of the impact hypothesis V. Hartman wrote: " It is difficult to imagine that two celestial bodies grow side by side from the same orbital layer of matter, but at the same time one of them takes all the iron, while the other remains practically without it».

3) Legends of some peoples (for example, Dogon, West Africa) tell about the time when there was no Moon in the sky, and about the appearance of a new star. Contrary to this, the results of computer simulations of the capture of the Moon by the Earth (jokingly called the “marital” hypothesis) show that the likelihood of such a capture is very small.

Much more likely is a collision or ejection of the proto-moon by Earth's gravity beyond the Earth's orbit. The Moon's low density and small iron core could be explained by the assumption that it formed outside the terrestrial planets (Mercury, Venus, Earth and Mars), but in this case it is impossible to explain the deficiency of volatile elements, which are abundant there. It is difficult to find a place in the solar system with both a low content of one and the other.

4) One of the main goals of the American space missions to the Moon in the 1960s and 70s was to find evidence in favor of one or another of the three above

named hypotheses of the origin of the Moon. During the Apollo program, 385 kg of lunar material was delivered to Earth. Already his first analyzes revealed significant disagreements between the results obtained and all three hypotheses.

Most experts believe that the currently available facts testify in favor of a hypothesis that did not yet exist before the flight of spacecraft to the Moon - the hypothesis of a catastrophic collision. To explain the iron deficiency on the Moon, we had to make the assumption that at the time of the collision (4.5 billion years ago) gravitational pull had already occurred in the depths of both bodies. differentiation substances when heavy chemical elements sank down and formed the core, and lighter ones floated to the surface and formed the mantle, crust, hydrosphere And atmosphere.

This assumption has no geological justification, but, nevertheless, the catastrophic hypothesis of the origin of the Moon is now considered the most acceptable.

Evolution of the Earth-Moon system. Let us now consider how the Earth and the Moon have coexisted since fate brought them together. The main driving force of their interaction was and remains tidal friction. The tidal force on Earth is the resultant of two forces: the attraction of the Moon or Sun and the centrifugal force of the Earth's rotation around the common Earth-Moon center (called barycenter system and is located in the Earth’s mantle at a depth of 1700 km) or Earth-Sun (Fig. 3).

At the center of the Earth these forces balance each other, but at the point A attraction prevails, and at the point IN- centrifugal force. These are the points of maximum tide on the surface of the planet.

Due to the daily rotation of the Earth in places of tidal protrusions A And IN visits the same point on the earth's surface twice a day. Residents of coasts and islands are well aware of the tides, when the water rises and falls twice a day. In some places, due to a combination of circumstances (current direction, narrow bays and river mouths), the height of the sea tide reaches 10 m, and, for example, at the mouth of the Severn River or in the Bay of Fundy (England) it reaches 16 m.

But tides are not only observed in the ocean. The solid Earth, attracted by the Moon and the Sun, behaves like a spring and is deformed, i.e. the solid body of the Earth also experiences a tide. These phenomena are called earth tides . The highest height of the earth's tide at the equator is 55 cm, and at the latitude of Kiev - about 40 cm. It is to this height that we rise and fall twice a day, slowly and continuously, 6 hours up, 6 hours down.

Since there is no fixed reference point against which such movements could be observed, this phenomenon remains unknown to many. But high-precision instruments (gravimeters, tiltmeters) reliably record the earth's tides. In this case, the observation point moves away from the center of the Earth by only one ten-millionth of the Earth’s radius (Earth’s radius ≈ 6400 km).

Gravimeters record this movement as a decrease in gravity, because gravity decreases with increasing distance from the center of the Earth.

During tides, both in the ocean and in the earth's firmament, due to the viscosity of the substance and the friction of water along the bottom and shores of reservoirs, part of the energy of the rotational movement of the Earth is dissipated in the form of heat. Tidal protrusions from friction A And IN do not have time to fall quickly and are carried forward by the Earth in the course of its rotation (Fig. 3). Moon's attraction to the ledge A(more than protrusion IN) slows down the daily rotation of the Earth, and gravity protrudes A Moon (more than a ledge IN) spins our natural satellite in orbit.

Due to the first effect, the Earth slows down its rotation around its axis, and due to the second, the Moon moves away from the Earth. True, the figures that describe the increase in the day and the lengthening of the radius of the Lunar orbit are extremely small: the day increases by 0.002 s per 100 years, and the Moon moves away from the Earth by 3 cm/year. Laser determinations of the distance to the Moon, carried out in 1969–2001 using corner reflectors installed on the Moon, give a value of 3.81 ± 0.07 cm/year for increasing the radius of the lunar orbit.

These seemingly insignificant quantities cause significant changes on a cosmological time scale. In addition, when the Moon was closer to our planet, their interaction was more intense: the days on Earth increased more significantly, and our natural satellite moved away faster (Fig. 4).

This is confirmed not only by the results of astronomical observations. There are also paleontological, fossil evidence suggests that days on Earth were previously shorter.

During the growth process, some corals and mollusks, as well as algae, form not only annual rings, as is the case with trees, but also daily rings. Using these data, you can calculate the number of days throughout the year. Modern organisms produce 365 diurnal rings in one annual, while fossils produce more.

Thus, organisms living in Devonian period Paleozoic era (400 million years ago, when the first vertebrates—fish) just appeared—accumulated 400 daily layers per year, and those who lived in Proterozoic(670 million years ago) – 435.

Astronomers do not know the reasons that, throughout the history of the Earth, could significantly influence the length of the year - the period of the Earth’s revolution around the Sun. Thus, the year did not change noticeably during this long period of time, only the length of the day changed.

It is easy to calculate from these observations that in Devon the day lasted 22 modern hours, and 670 million years ago ( Proterozoic era) were equal to only 20 modern hours. Previously, the days were even shorter, but there is no paleontological evidence of this at this time.

According to the calculations of astronomers studying the origin of planets and the past of the solar system, the initial period of rotation of the Earth around its axis (day) was 10 hours. The day on the giant planets Jupiter and Saturn is close to this value, the enormous inertia of which and numerous satellites that act inconsistently contributed to the preservation of their primary daily rotation. Uranus and Neptune have slowed down their axial rotation slightly: a day on Uranus lasts about 17 hours, and on Neptune - about 16.

The Earth will slow down its rotation until the day is equal to the period of revolution of the Moon around our planet. Their total rotation period will then be 47 current days. The Earth and the Moon will rotate facing each other with tidal protrusions, on the same side, as if connected by a bridge, like a dumbbell.

By the way, the Moon used to rotate around its axis much faster, and then it was possible to admire not only one side of our satellite. However, the tides that Earth’s gravity causes on the Moon are significantly greater than those caused by the Moon on Earth, since the mass of our planet is 81 times greater, and the force of gravity on the surface of our satellite is 6 times less.

Lunar tides have long slowed down the rotation of the Moon, and its tidal protrusion is now always directed towards the Earth. Such a rotation of the satellite around the central planet and around its axis, when one side of the satellite is always facing the planet, and the period of rotation around the central body and around the axis coincide, is called synchronous.

Surprising in this regard is the foresight of the famous German philosopher Immanuel Kant(1724–1804) at a time when there was no scientific data on this issue yet.

In his work “General History and Theory of Heaven” in 1754, he wrote: “ If the Earth is steadily approaching the moment of suspension of its rotational motion, then the period during which this change occurs will be completed when the surface of the Earth is at rest in relation to the Moon, that is, when the Earth begins to rotate around its axis at that the very time at which the Moon makes a revolution around the Earth, therefore, when the Earth will always face the same side to the Moon. The reason for this state is the movement of a liquid substance covering part of its surface only to a very small depth. This immediately shows us the reason why the Moon, in its rotation around the Earth, always faces it with the same side».

It is curious that the height of the tidal ridge on the Moon is now 2 km. This is 100 times more than the tide that our planet would cause at its current distance from the Moon. Obviously, at the time when such a high tide formed, our natural satellite was significantly closer to the Earth. For such a huge tide, the distance would not be 380 thousand km, as it is now, but 5 times less.

The moon then had molten interiors, which, cooling, hardened and retained this huge tidal protrusion in its body, as a memory of that long-ago era. This also indicates that the Moon began to rotate synchronously with its revolution around the Earth already when the distance between them was only 75 thousand km. This happened less than two billion years ago.

Let us now turn to the Earth. As mentioned, the length of the day and month in the distant future will be equal to each other and will be 47 current days. For this process to be completed, it will take a long time - about 50 billion years. Let us recall that the age of the Earth and planets is about 4.5 billion years.

This would have stabilized the process of joint rotation of the Earth and the Moon, if not for the Sun. The fact is that solar tides also slow down the daily rotation of the Earth. Although they are two times smaller than the lunar ones, they do not change over time.

And if the braking effect of the Moon on the daily rotation of the Earth stops at the moment when the day and month become equal, then the influence of the Sun on this process will continue. As a result, the day on Earth will continue to increase, and as a result, our planet will rotate around its axis more slowly than the Moon around it.

In this situation, the tides caused by the Moon on Earth will affect its rotation in the direction opposite to the previously considered case, i.e. the Earth will accelerate in its rotation, and the Moon will slow down in orbit. The reverse process will begin: the day will begin to decrease, and the Moon will begin to approach the Earth, and this will continue until the Moon approaches the so-called Roche limit.

For a satellite with zero strength (liquid, individual fragments of a solid body), this limit is approximately 1.5 radii from the surface of the central planet. Here, the centrifugal force of the Moon's revolution and the gravity of the planet, acting in opposite directions (their resultant is the tidal force), will prevail over the force of gravity on the surface of the satellite and tear it apart. A ring of many small satellites forms around the Earth.

Such examples are known in our solar system: the giant planets Jupiter, Saturn, Uranus and Neptune all have rings near the surface, although the origin of these rings is not necessarily related to tides. Obviously, the satellites of these planets could not form near the Roche limit.

In the Earth-Moon system, tidal processes occur extremely slowly. It has already been mentioned: for a day on Earth to become equal to the length of a month, it takes about 50 billion years. And for the Moon to return back to the Earth, it takes too long, even in cosmological scale.

In the Solar System there are many examples of the effective effect of tides on the rotational motion of celestial bodies. The planets Mercury and Venus have slowed down significantly as a result of the influence of solar tides on them, and their day (period of rotation around their axis) lasts 58.6 and 243 Earth days, respectively.

The synchronous rotation is followed by the small satellites of Mars Phobos and Deimos. On the large satellite Io, closest to Jupiter, the height of the tide, frozen during synchronous rotation, is 3 km. Only as a result of the satellite moving along an elongated (eccentric) orbit does this height change by 84 meters. Moreover, due to the deformation of the satellite’s body, 10 times more heat is released than on the Moon from the decay of radioactive substances. As a result, Io has volcanoes that are more powerful than those on Earth (Fig. 5).

The large moons of Jupiter, Saturn and Uranus, and Neptune's largest moon Triton, rotate synchronously. Pluto and Charon are prime examples of tidal locking. In this system, not only Charon rotates synchronously, but Pluto also faces Charon with one side all the time, they rotate with a period of 6.4 days, as if connected by a jumper.

As a result, we emphasize that tidal friction is an important factor in the evolution of cosmic systems, not only planets and satellites, but also multiple star clusters and even galaxies.

Dictionary
Atmosphere(from the Greek ατμος - steam and σφαϊρα - ball) - the air shell of the Earth.
Hydrosphere(from the Greek υδωρ - water and σφαϊρα - ball) - the water shell of the Earth.
Gravimeter(from Latin gravis - heavy and Greek μετρεω - to measure) - a device for measuring the magnitude of gravity.
Devonian(from the name of the English county of Devonshire) – fourth period Paleozoic era from 419 to 359 million years ago.
Differentiation(from Latin differentia - difference) - division of the whole into qualitatively different parts.
Cosmological(from the Greek κοσμοζ - space, universe) - everything that relates to the Universe.
Climax(from Latin culmen - peak) - here is the maximum height of the luminary.
Lithosphere(from the Greek λιτος - stone and σφαϊρα - ball) - the stone shell of the Earth.
Mantle(from the Greek μαντιον - cover) - the rocky shell of the Earth from the core to the earth's crust.
Paleozoic(from the Greek παλαιος - ancient ςωη - life) - the third geological era in the history of the Earth from 541 to 251 million years ago.
Paleontology(from the Greek παλαιος - ancient, οντος - essence and λογος - teaching) - the science of the fossil remains of living organisms.
Proterozoic(from the Greek προτερος - previous) - the second geological era in the history of the Earth from 2500 to 541 million years ago.
Protoplanetary, protosolar(from the Greek πρωτος - first) - the primary nebula from which the Sun and planets were formed at one time.
Siderophiles(from the Greek σίδηρος - iron and φίλεω - love) - chemical elements adjacent to iron in the periodic table.
Synchronous(from the Greek συγχρονο - simultaneously) - coincidence in the period of oscillation of two or more processes.
Tectonics(from the Greek τεκτονικη - construction) - the science of the structure and movements of the earth's crust and the masses located under it (lithospheric plates).

I.A. Dychko, candidate of physical and mathematical sciences, Poltava

MOSCOW, June 22 - RIA Novosti. Assumptions that the Moon may leave the orbit of the Earth’s satellite in the future contradict the postulates of celestial mechanics, say Russian astronomers interviewed by RIA Novosti.

Earlier, many online media, citing the words of the general director of the “space” Central Research Institute of Mechanical Engineering, Gennady Raikunov, reported that in the future the Moon could leave the Earth and become an independent planet moving in its own orbit around the Sun. According to Raikunov, in this way the Moon can repeat the fate of Mercury, which, according to one hypothesis, was a satellite of Venus in the past. As a result, according to the general director of TsNIIMash, conditions on Earth may become similar to those on Venus and will be unsuitable for life.

“This sounds like some kind of nonsense,” Sergei Popov, a researcher at the Sternberg State Astronomical Institute of Moscow State University (SAISH), told RIA Novosti.

According to him, the Moon is indeed moving away from the Earth, but very slowly - at a speed of about 38 millimeters per year. “Over a few billion years, the Moon’s orbital period will simply increase by one and a half times, and that’s all,” Popov said.

“The moon cannot completely leave. She has nowhere to get the energy to escape,” he noted.

Five week day

Another traffic police officer, Vladimir Surdin, said that the process of the Moon moving away from the Earth will not be endless; it will ultimately be replaced by an approach. “The statement “The Moon can leave the Earth’s orbit and turn into a planet” is incorrect,” he told RIA Novosti.

According to him, the removal of the Moon from the Earth under the influence of tides causes a gradual decrease in the speed of rotation of our planet, and the speed of the satellite’s departure will gradually decrease.

In about 5 billion years, the radius of the lunar orbit will reach its maximum value - 463 thousand kilometers, and the duration of the earth's day will be 870 hours, that is, five modern weeks. At this moment, the speed of rotation of the Earth around its axis and the Moon in orbit will become equal: the Earth will look at the Moon with one side, just as the Moon is now looking at the Earth.

“It would seem that tidal friction (the braking of its own rotation under the influence of lunar gravity) should disappear. However, solar tides will continue to slow down the Earth. But now the Moon will outstrip the Earth’s rotation and tidal friction will begin to slow down its movement. As a result, the Moon will begin to approach On Earth, however, it is very slow, since the strength of solar tides is small,” the astronomer said.

“This is the picture that celestial-mechanical calculations paint for us, which today, I think, no one will dispute,” noted Surdin.

Losing the Moon won't turn Earth into Venus

Even if the Moon disappears, it will not turn the Earth into a copy of Venus, Alexander Bazilevsky, head of the laboratory of comparative planetology at the Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences, told RIA Novosti.

“The Moon’s departure will have little effect on the conditions on the Earth’s surface. There will be no ebbs and flows (they are mostly lunar) and the nights will be moonless. We’ll survive,” the agency’s interlocutor said.

“The Earth may follow the path of Venus, with terrible heating, because of our stupidity - if we bring it with emissions of greenhouse gases to a very strong heating. And even then, I’m not sure that we will be able to ruin our climate so irreversibly,” the scientist said.

According to him, the hypothesis that Mercury was a satellite of Venus, and then left the satellite’s orbit and became an independent planet, was indeed put forward. In particular, American astronomers Thomas van Flandern and Robert Harrington wrote about this in 1976, in an article published in the journal Icarus.

“Calculations have shown that this is possible, which, however, does not prove that it was so,” Bazilevsky said.

In turn, Surdin notes that “later work practically rejected it (this hypothesis).”

MOSCOW, June 22 - RIA Novosti. Assumptions that the Moon may leave the orbit of the Earth’s satellite in the future contradict the postulates of celestial mechanics, say Russian astronomers interviewed by RIA Novosti.

Earlier, many online media, citing the words of the general director of the “space” Central Research Institute of Mechanical Engineering, Gennady Raikunov, reported that in the future the Moon could leave the Earth and become an independent planet moving in its own orbit around the Sun. According to Raikunov, in this way the Moon can repeat the fate of Mercury, which, according to one hypothesis, was a satellite of Venus in the past. As a result, according to the general director of TsNIIMash, conditions on Earth may become similar to those on Venus and will be unsuitable for life.

“This sounds like some kind of nonsense,” Sergei Popov, a researcher at the Sternberg State Astronomical Institute of Moscow State University (SAISH), told RIA Novosti.

According to him, the Moon is indeed moving away from the Earth, but very slowly - at a speed of about 38 millimeters per year. “Over a few billion years, the Moon’s orbital period will simply increase by one and a half times, and that’s all,” Popov said.

“The moon cannot completely leave. She has nowhere to get the energy to escape,” he noted.

Five week day

Another traffic police officer, Vladimir Surdin, said that the process of the Moon moving away from the Earth will not be endless; it will ultimately be replaced by an approach. “The statement “The Moon can leave the Earth’s orbit and turn into a planet” is incorrect,” he told RIA Novosti.

According to him, the removal of the Moon from the Earth under the influence of tides causes a gradual decrease in the speed of rotation of our planet, and the speed of the satellite’s departure will gradually decrease.

In about 5 billion years, the radius of the lunar orbit will reach its maximum value - 463 thousand kilometers, and the duration of the earth's day will be 870 hours, that is, five modern weeks. At this moment, the speed of rotation of the Earth around its axis and the Moon in orbit will become equal: the Earth will look at the Moon with one side, just as the Moon is now looking at the Earth.

“It would seem that tidal friction (the braking of its own rotation under the influence of lunar gravity) should disappear. However, solar tides will continue to slow down the Earth. But now the Moon will outstrip the Earth’s rotation and tidal friction will begin to slow down its movement. As a result, the Moon will begin to approach On Earth, however, it is very slow, since the strength of solar tides is small,” the astronomer said.

“This is the picture that celestial-mechanical calculations paint for us, which today, I think, no one will dispute,” noted Surdin.

Losing the Moon won't turn Earth into Venus

Even if the Moon disappears, it will not turn the Earth into a copy of Venus, Alexander Bazilevsky, head of the laboratory of comparative planetology at the Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences, told RIA Novosti.

“The Moon’s departure will have little effect on the conditions on the Earth’s surface. There will be no ebbs and flows (they are mostly lunar) and the nights will be moonless. We’ll survive,” the agency’s interlocutor said.

“The Earth may follow the path of Venus, with terrible heating, because of our stupidity - if we bring it with emissions of greenhouse gases to a very strong heating. And even then, I’m not sure that we will be able to ruin our climate so irreversibly,” the scientist said.

According to him, the hypothesis that Mercury was a satellite of Venus, and then left the satellite’s orbit and became an independent planet, was indeed put forward. In particular, American astronomers Thomas van Flandern and Robert Harrington wrote about this in 1976, in an article published in the journal Icarus.

“Calculations have shown that this is possible, which, however, does not prove that it was so,” Bazilevsky said.

In turn, Surdin notes that “later work practically rejected it (this hypothesis).”

quoted1 > > > Why is the Moon moving away from us?

The moon is moving away from the Earth: description of the process, the influence of gravity of the planet and satellite, interaction of objects in space, features of orbit and speed with photos.

We are used to the Moon and Earth waltzing side by side. This is a wonderful couple that did not just form together. It was our planet, after a collision with another object, that gave life to the satellite. They grew together and have been in contact for 4.5 billion years.

And what have we come to? Our faithful companion Luna, it turns out, has decided to leave us. In the past, the distance between the Moon and the Earth was smaller, and time flew faster. Even 620 million years ago, the day covered 21 hours. Now they have grown to 24 hours, and the satellite is 384,400 km away.

Every year The Moon is moving away from the Earth by 1-2 cm, due to which 1/500th of a second is added every century. And why does this happen? Has she really found a new object to spin? Or is our planet not good enough? No need to blame her. It's all just nature.

The Earth and Moon mutually exchange gravitational influence. Because of this, their shapes change and bulges are created.

These bulges function as a brake, which slows down the speed of their rotation. Previously, the Moon rotated much faster. But the slowdown not only gave us a longer day, but also weakened the connection with the satellite. It is believed that this will last another 45 billion years. The sun, of course, will transform into a red giant and will fry the planet. And our day will stretch to 45 hours. That's when Luna decides to break the connection forever.

Don't think that we alone will be abandoned. Many moons will leave their parental homes, and some will even crash into planets, as Phobos plans to do with Mars.

Now the Moon is moving away from the Earth. But when the day and month become equal, it will begin to approach. Will the Moon fall to Earth or not?

What is the future for the Earth-Moon system? If we extrapolate modern data on the rate of removal of the Moon, we can draw the following conclusion. The length of the day and month will increase all the time. In this case, the day will grow faster than the month, and in the distant future they will become equal. As a result, the Moon will always be visible from only one side of the Earth.

A system in which the planet and the satellite always “look” at each other with the same side already exists in the Solar System. These are Pluto and Charon. This is the most stable state in a TWO-body system. But the Earth is much closer to the Sun. Tidal forces from the Sun also slow down the Earth's rotation: the amplitude of solar tides is only slightly less than half the lunar tides. Therefore, after the Earth and Moon rotate synchronously, the Sun will continue to slow down the Earth's rotation. The Earth will begin to rotate around its axis SLOWER than the Moon in orbit. And this means that the Moon will be BELOW the synchronous orbit. Consequently, it will begin to fall to Earth.

Will all this end in a grandiose catastrophe in the history of the Earth?

A good scenario for a horror film: The moon is getting closer and closer, and it is impossible to stop it. After all, if the satellite ends up below the synchronous orbit, then its irreversible fall begins. Or not?

The satellite located below the synchronous orbit will “fall” on the planet, and the one located above will “fly away” from it. True, there is a significant clarification here. This will only happen if the planet's rotation speed remains constant. This is true for small satellites. And for the big ones? At what mass of the satellite can it already be considered large?

The answer is simple: if the orbital angular momentum of the satellite is comparable in magnitude to the planet’s own angular momentum. In this case, the removal or approach of the satellite will significantly change the speed of rotation of the planet.

A simple calculation shows that in the Earth-Moon system, most of the total angular momentum falls on the Moon, and not on the Earth. Indeed, the angular momentum of the Earth is equal to:

Here I= 0.33 – dimensionless moment of inertia of the Earth, M- its mass, R– equatorial radius, V – linear velocity at the equator.

The orbital momentum of the Moon is:

Here m– mass of the Moon, r is the average radius of its orbit, v is the orbital speed.

The mass of the Moon is 80 times less than the Earth, its orbital radius is 60 times greater than the radius of the Earth, and its orbital speed (1 km/sec) is 2 times greater than the equatorial rotation speed of the Earth (500 m/sec). Consequently, the Moon's orbital momentum is approximately four times greater than the Earth's rotational moment. Therefore, under no circumstances will the Moon be able to fall to Earth, even if in the distant future it ends up in a synchronous orbit.

As an example, let's assume that the Moon is in its current orbit, and the Earth does not rotate on its axis at all. In this case, kinetic energy will be transferred from the Moon to the Earth. The Earth will gradually begin to rotate, and the Moon will approach it: fall to the Earth. But it won't fall.

How close will the Moon be to Earth?

Orbital angular momentum is proportional to the orbital radius and speed. Orbital speed is inversely proportional to the square root of the radius. Therefore, the orbital momentum is proportional to the square root of the radius. If the orbital radius decreases by two percent, the torque will decrease by one percent. And this percentage, due to conservation, will be transferred to the Earth. Considering that the modern period of the Earth's rotation of one day corresponds to 25 percent of the lunar orbital momentum, then one percent will correspond to a period of 25 days. This period will be shorter than the lunar month, which, due to Kepler's third law, will decrease by only three percent and will be approximately 28 days. That is, the Earth will rotate FASTER than the Moon. Consequently, the Moon will NOT be able to approach the Earth even by 2 percent, but will approach a little less.

The future of the Earth-Moon system in general terms is as follows.

At first, the Moon will continue to move away from the Earth, receiving angular momentum from it. But the Earth does not have much angular momentum left - 25% of the Moon’s orbital angular momentum. Therefore, the maximum that the Moon can get is to increase its angular momentum by 25%. The radius of its orbit will increase by 1.5 times (1.25 squared). And the lunar month will increase approximately 2 times (according to Kepler’s Third Law, you need to raise 1.5 to the power of 3/2) and will be 60 days. Accordingly, the earth's day will also increase to 60 days. This is the MAXIMUM distance that the Moon can move away from the Earth.

How long will it take the Moon to move this distance from the Earth (half the radius of its current orbit)?

The distance to the moon is 380 thousand km, the removal rate is 3.8 cm/year. It is easy to calculate that the Moon will travel half its radius in five billion years if it moves away at a constant speed. But the removal rate will gradually decrease. So we'll have to add a few more billion years.

What will we do next?

The Sun will continue to slow down the Earth's rotation (solar tides).

But as soon as the Earth's rotation slows down, the Moon will move a little closer and the rotation will speed up again. The Sun will slow it down again, and the Moon will again approach and speed it up, and so on. The Earth is, in a sense, lucky to have the Moon. During its youth, when our planet rotated very quickly, it transferred its momentum to the Moon and thus preserved it. Indeed, under the influence of lunar tides, the Earth's angular momentum is not lost, but is only redistributed in the Earth-Moon system. And under the influence of weaker solar tides it is lost. But these tides can only take away angular momentum from the Earth. But for a long time now the main part of the angular momentum of the Earth-Moon system has been concentrated in the orbital motion of the Moon. And the solar tides cannot do anything with it. The Earth gave the lion's share of its rotation to the Moon, and there this share remains safe and sound. And after many billions of years, the Moon will gradually return its rotation to the Earth.