Why is the moon receding. What is the maximum distance the moon can be from the earth? Why is the Moon so necessary for the Earth

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

Earlier, many Internet media, citing the words of Gennady Raikunov, director general of the "space" Central Research Institute of Mechanical Engineering, 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, the conditions on Earth may become similar to those of Venus and will be unsuitable for life.

"It sounds like some kind of nonsense," Sergey Popov, a researcher at the Sternberg State Astronomical Institute of Moscow State University (GAISh), told RIA Novosti.

According to him, the Moon is really moving away from the Earth, but very slowly - at a speed of about 38 millimeters per year. "In a few billion years, the period of the Moon's revolution will simply increase by a factor of one and a half, and that's all," Popov said.

"The moon cannot completely leave. She has nowhere to get energy in order to escape," he said.

Five week day

Another employee of the SAI Vladimir Surdin said that the process of moving the Moon away from the Earth would not be endless, eventually it would 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 the tides causes a gradual decrease in the speed of rotation of our planet, and the speed of the departure of the satellite 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 speeds of rotation of the Earth around its axis and the Moon in orbit will become equal: the Earth will look at the Moon on one side, just as the Moon is now looking at the Earth.

“It would seem that tidal friction (the deceleration 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 outpace the Earth’s rotation and tidal friction will begin to slow down its movement. As a result, the Moon will begin to approach The Earth, however, is very slow, since the strength of the solar tides is small," the astronomer said.

"Such a picture is drawn to us by celestial-mechanical calculations, which no one, I think, will dispute today," Surdin noted.

The loss of the moon will not turn the Earth into Venus

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

"On the conditions on the surface of the Earth, the departure of the moon will have little effect. There will be no ebb and flow (they are mostly lunar) and the nights will be moonless. We will survive," the agency's source said.

“On the path of Venus, with a terrible warming up, the Earth can go because of our stupidity - if we bring it with greenhouse gas emissions to a very strong warming up. 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 orbit of the satellite and became an independent planet, was really 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 works have practically rejected it (this hypothesis)."

The moon is now moving away from the earth. But when the day and month are equal, it will begin to approach. Will the moon fall to earth or not?

What is the future of the Earth-Moon system? If we extrapolate modern data on the rate of removal of the Moon, we can draw the following conclusion. The duration of the day and month will increase all the time. At the same time, the day will grow faster than the month, and in the distant future they will equalize. 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 all the time “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 the system of TWO bodies. But the Earth is much closer to the Sun. Tidal forces from the Sun also slow down the rotation of the Earth: the amplitude of solar tides is only two and a half times less than that of the moon. Therefore, after the Earth and the Moon rotate synchronously, the Sun will continue to slow down the rotation of the Earth. The Earth will begin to rotate around its axis SLOWER than the Moon in its orbit. And this means that the Moon will be BELOW the synchronous orbit. Therefore, it will begin to fall to the Earth.

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

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

A satellite below the synchronous orbit will “fall” onto the planet, and one above it will “fly away” from it. True, there is a significant clarification here. This will only happen if the planet's rotational 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 satellite's orbital angular momentum 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:

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

The orbital moment of the moon is:

Here m is the mass of the moon, r is the average radius of its orbit, v is the orbital velocity.

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 the orbital speed (1 km / s) is 2 times greater than the equatorial speed of the Earth's rotation (500 m / s). Therefore, the orbital momentum of the Moon is about four times greater than the angular momentum of the Earth. Therefore, the Moon, under no circumstances, will not be able to fall to the Earth, even if in the distant future it will be in a synchronous orbit.

As an example, suppose 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 is the moon to the earth?

The orbital angular momentum is proportional to the radius of the orbit and the velocity. The orbital velocity 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 radius of the orbit is reduced by two percent, then the momentum will be reduced by one percent. And this percentage, by virtue of conservation, will be transferred to the Earth. Considering that the modern period of the Earth's rotation in one day corresponds to 25 percent of the lunar orbital moment, 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 only by three percent and will be approximately 28 days. That is, the Earth will rotate FASTER than the Moon. Therefore, 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 this.

At first, the Moon will continue to move away from the Earth, receiving momentum from it. But the Earth has not 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 by about 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 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 away from the Earth at this distance (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 half of the radius of the Moon will pass in five billion years if it moves away at a constant speed. But the removal rate will gradually decrease. So we have to throw in 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 rotation of the Earth slows down, the Moon will approach a little bit and the rotation will speed up again. The sun will slow it down again, and the moon will approach and speed it up again, and so on. The Earth is, in a sense, lucky to have the Moon. At the time of its youth, when our planet rotated very quickly, it transferred its momentum to the moon and thus preserved it. Indeed, under the action of lunar tides, the angular momentum of the Earth is not lost, but only redistributed in the Earth-Moon system. And under the influence of weaker solar tides is lost. But these tides can only take angular momentum from the Earth. But for a long time the bulk of the angular momentum of the Earth-Moon system has been concentrated in the orbital motion of the Moon. And the solar tides can't do anything with it. The Earth has given the lion's share of its rotation to the Moon, and there this share is safe and sound. And after many billions of years, the Moon will gradually return the rotation of the Earth.

At any given time, the Moon is no closer than 361,000 and no further than 403,000 kilometers from the Earth. The distance from the Moon to the Earth changes because the Moon revolves around the Earth not in a circle, but in an ellipse. In addition, the Moon is little by little moving away from the Earth by an average of 5 centimeters per year. People have been observing the gradually decreasing moon for many centuries. A day may come when the Moon will break away from the Earth and fly away into space, becoming an independent celestial body. But this may not happen. The balance of gravitational forces keeps the Moon firmly in Earth orbit.

Interesting fact: The moon moves away from the earth by about 5 centimeters every year.

Why is the moon moving away from the earth?

Any moving body wants by inertia to continue its path in a straight line. A body moving in a circle tends to break away from the circle and fly tangentially to it. This tendency to break away from the axis of rotation is called centrifugal force. You feel the centrifugal force at the playground, on the high-speed swings, or when the car swerves sharply and pushes you against the door.

The word "centrifugal" means "running away from the center". The moon also strives to follow this force, but it is kept in orbit by the force of the earth's gravity. The moon remains in orbit because the centrifugal force is balanced by the earth's gravity. The closer to the planet its satellite is, the faster it revolves around it.

At any given time, the Moon is no closer than 361,000 and no further than 403,000 kilometers from the Earth. The distance from the Moon to the Earth changes because the Moon revolves around the Earth not in a circle, but in an ellipse. In addition, the Moon is little by little moving away from the Earth by an average of 5 centimeters per year. People have been observing the gradually decreasing moon for many centuries. A day may come when the Moon will break away from the Earth and fly away into space, becoming an independent celestial body. But this may not happen. The balance of gravitational forces keeps the Moon firmly in Earth orbit.

Interesting fact: The moon moves away from the earth by about 5 centimeters every year.

Why is the moon moving away from the earth?

Any moving body wants by inertia to continue its path in a straight line. A body moving in a circle tends to break away from the circle and fly tangentially to it. This tendency to break away from the axis of rotation is called centrifugal force. You feel the centrifugal force at the playground, on the high-speed swings, or when the car swerves sharply and pushes you against the door.

The word "centrifugal" means "running away from the center". The moon also strives to follow this force, but it is kept in orbit by the force of the earth's gravity. The moon remains in orbit because the centrifugal force is balanced by the earth's gravity. The closer to the planet its satellite is, the faster it revolves around it.