Will the moon fall? What is the probability? What would happen if it really falls?

Will the moon fall? If someone asks this question, they may be considered a fool. Look up, the moon these days is like a half-torn pancake, with the other half hanging crookedly in the night sky. It has been waxing and waning like this for countless years, and people have been recording it for thousands of years. How could it fall?

But some people are really worried about it falling. According to online news, the Americans have made a new science fiction film called "Moonfall" or "Moonfall", which tells the story of the moon falling. When the catastrophe is about to come, a group of rabble are ordered to take charge of the situation, hastily set up a team, and try to turn the tide beyond their ability. How well it can be saved will have to wait until the film is released in 2022 to know.

In fact, the moon has not always been like this. It has been changing for billions of years. So is it really possible that it could fall off? Let's find out.

Origin of the Moon

Science generally does not talk about the moon, but only says moon, because the so-called moon is actually a planet, and this planet did not exist forever, but was "born" from the "falling in love" between the newly born Earth and a planet the size of Mars. Therefore, the moon can actually be said to be the son or daughter of the Earth.

In ancient Greek mythology, there is a goddess named Theia, who is the mother of the moon goddess Selene. Therefore, scientists call the planet that hit the earth "Theia", which means that the earth is the father. 4.5 billion years ago, Theia floated from outside the earth's orbit and had a wild hug with the earth. After the earth-shaking, the whole planet melted, merged together, and gradually condensed again. The lava and debris condensed in space to become the moon.

The Earth and Theia became one, with a mass 1/8 larger than the original Earth, while the Moon became a satellite orbiting the Earth, just like children protecting their parents.

It was this earth-shattering collision that caused the Earth's rotation axis to tilt, forming an angle of 23.44° between the equator and the ecliptic, giving the Earth four seasons of spring, summer, autumn and winter. The moon's tidal force controlled the tides of the Earth's oceans, making the Earth more lively and playing an important basic role in the emergence and evolution of life.

Therefore, this seemingly accidental disaster turned out to be a blessing in disguise for the Earth, making it the only paradise for life in the solar system, which gave rise to the hopes and developments of literati and poets.

So will the moon continue like this?

Of course not. The moon is not static. When it was first born, it was very close to the earth. The earth and the moon were like two red fireballs, burning each other. But due to the influence of angular momentum inertia and tidal force, as well as some complex factors, the moon has been moving away from the earth since its birth, just like children will eventually leave their parents when they grow up.

The moon is moving away from the earth at a speed of about 4 centimeters per year, so in 100 million years it is 400 million centimeters, or 4,000 kilometers, and in 4.5 billion years it is 180,000 kilometers away. In fact, the early moon was moving away from the earth faster, which is why the moon is currently 384,000 kilometers away from the earth on average.

The moon is still moving away from the earth. Will it continue to do so forever? It's hard to say.

Is it possible for the moon to return to the arms of its parents?

It is best not to come back, because coming back would mean a devastating disaster. In fact, there is no need to describe how big this disaster is, because 65 million years ago, an asteroid with a diameter of about 10 kilometers destroyed the earth's ecology, causing the extinction of dinosaurs that dominated the earth for 160 million years, and at the same time extinct 85% of species.

The diameter of the moon is 3,476 kilometers, which is incomparable with the 10-kilometer asteroid. Such an impact cannot be calculated by tons of explosive equivalent. It is an undoubted destruction, not the destruction of the ecology, but the reconstruction of the earth after destruction.

Will there be such a collision between the earth and the moon? At least there is no sign of this at present, but it is not impossible. The probability is that the moon will be hit by an asteroid. Therefore, don't think that as long as the asteroid does not hit the earth, there will be no problem. If it hits the moon, it will also cause disaster to others.

It is often said that the Earth and the Moon protect each other, and the dense craters on the back of the Moon have blocked many bullets for the Earth and protected the Earth since ancient times. This is true, but these bullets blocked since ancient times are really just "bullets", not cannonballs. If a huge asteroid "cannonball" hits the Moon, it is very likely to knock the Moon's orbit off track and cause the Moon to gradually fall towards the Earth.

How big should this "cannonball" be?

This "cannonball" must be very large. I think 10 kilometers is not enough to change the orbit of the moon. At least an asteroid of 100 kilometers is needed. When such a large asteroid hits the moon along the direction of revolution, it will increase the moon's revolution speed, so that the moon will leave the earth faster; and when it hits the moon head-on from the direction of revolution, the moon's revolution speed will decrease, resulting in the moon's revolution speed being less than the moon's orbit speed around the earth, and it will gradually be pulled down by the earth's gravity and eventually fall to the earth.

The side effect of this impact is that a large amount of debris will fly into space, some of which will fly far away, and a large part will fall to the earth, causing major disasters on the earth. Of course, the ultimate disaster is that the moon falls to the earth and everything is destroyed.

The impact of an asteroid of this mass, as long as its speed is fast enough, reaching 20 to 30 kilometers per second, will cause a change in the moon's orbital speed no matter from what angle it hits the moon. Only the change in the orbital speed is the fundamental reason for its fall and movement away from the earth.

The orbital velocity is the equilibrium speed of an object against gravity, following the formula: v²=GM/r, where v represents the orbital velocity, G is the gravitational constant, M is the mass of the celestial body dominated by gravity, and r is the distance. Any object relative to a gravitational source, as long as it reaches and maintains the orbital velocity, will form a balance with the gravitational source, and will neither move away nor be pulled down by gravity.

The lunar revolution speed is 1.023 km/s, which is the orbital speed of the moon in the high altitude orbit 384,000 km from the center of the earth. If the speed is higher than this, the gravity of the earth will not be able to hold the moon and will gradually move away; if the speed is lower than this, the moon will be pulled down by the gravity of the earth.

Therefore, for the moon to fall to the earth, its orbital velocity must be less than this speed. How much less should it be? In fact, there is no strict rule. The smaller it is, the faster it falls, and vice versa, it falls slower. That's all.

Nowadays, many science fiction films talk about disasters that the earth may encounter in the future. These disasters seem impossible to ordinary people, but some of them are happening already. For example, the extreme climate caused by the greenhouse effect is happening continuously. If it is not curbed, one day the disasters warned in science fiction films such as "Waterworld", "The Day After Tomorrow" and "Global Storm" will really occur.

Therefore, any incredible things are not completely impossible to happen, such as the moon falling. The problem is that humans do not have the ability to predict and respond to it now, and can only leave it to fate. This article is just my thoughts, without rigorous data support, and is just one person's opinion. Please do not take it seriously.

That’s it, welcome to discuss, thanks for reading.

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