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Could the Moon crash into the Earth? This is what science thinks

Could this sci-fi scenario happen in real life?

A collision between the Moon and the Earth would undoubtedly be catastrophic for life on the planet, it could even pass as a narrative for a science fiction film. But what does science say about it, can the Earth and the Moon really collide?

According to the plot of the movie Moonfall, a strangely mysterious and enormous force pulls the Moon out of orbit, causing it to inevitably fall towards the Earth. What follows is easier to imagine; an imminent collision between the two cosmic objects, but what are the chances of this being possible? Science answers the question posed by the film.

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Can the Moon crash into the Earth?

Although our logic, based on basic physics, leads us to believe that the Moon could crash into the Earth if we apply a mysterious force in the direction of the planet, the reality is that it doesn’t work as simply as that.

If a force 50 times greater than the Earth’s gravitational field were used to push the Moon towards the Earth, it would not be enough to move the satellite or to bring it so close to us that it would fall directly to Earth. The only thing that would happen would be that the Moon would change its orbit but without any dangerous approach to the planet.

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To understand why, we must first know that both bodies do not move independently of each other, but are within a system of orbital mechanics. That is to say, they are connected by their gravitational fields and affect each other.

In that sense, if the Moon is pushed towards the Earth through the center of mass of the orbital system, the action will not change the angular momentum. This can be described as the measure of rotational motion that depends intrinsically on the mass, velocity, and position of both bodies.

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The angular momentum of the Moon is constant, so as it approaches the Earth, it would have to accelerate its orbital motion. However, by applying a force toward the Earth all that is being achieved is a lateral move that will end up pushing the planet to change its orbit concerning the Sun, although not to a great extent.

In other words, if the Moon is pushed towards the Earth, a collision between the two would not occur, but rather an orbital change of the Moon around the Earth and consequently, an orbital change of the Earth around the Sun. Therefore, this would not be the way to cause the catastrophic collision, but there is still another way.

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A force against the lunar orbital motion

If you use the same magnitude as in the previous example, about 50 times the Earth’s gravitational field but this time in the opposite direction of the Moon’s orbital motion, things get a little worrisome. Doing this would now affect the angular momentum of the Moon, which means that the overall rotation rate will become much slower, enough for the Moon to plunge like a rock in free fall towards our planet.

Therefore, the only way the Moon could collide with the Earth would be simply to completely freeze the orbit of the natural satellite. This is the same as slowing down the Moon’s velocity to complete zero concerning the Earth. In this case, we should be concerned, because the orbital system would be broken and the Earth’s gravitational field would attract the satellite, increasing its acceleration as time goes by, just as gravity acts on a rock in free fall.

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The answer to whether the two bodies can collide, the answer is yes, but with a big but. For this to happen, there would have to be a mysterious force of great magnitude that would reduce the lunar rotation speed to zero, although such conditions are very unlikely to happen. In the meantime, we can continue to enjoy the amazing orbital system composed of our planet and its moon.

Story originally published in Spanish in Ecoosfera

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