Our satellite, the Moon, is located at an average distance of 384.400 kilometers from Earth. Each year it moves away about 3,4 centimeters. This means that over millions of years, the Moon may no longer be our satellite. What would happen if the scenario were the opposite? That is, if the Moon moved a little closer to our planet each year. This fact is known as the Roche limit. What is this Roche limit?
In this article we explain everything about it.
If the moon came closer to our planet
First of all, it should be mentioned that this is totally fictitious. The moon has no way to get close to our planet, so all of this is just an assumption. In fact, in reality, the moon will continue to move further and further away from Earth each year. Let's go back to the time when our planet was still newly formed and our satellite's orbit was closer than it is today. At that time, the distance between planet and satellite was smaller. Furthermore, the Earth rotated faster. Days only lasted six hours, and the moon took only 17 days to complete a full orbit.
The gravity exerted by our planet on the moon is what slowed its rotation. At the same time, the gravity exerted by the moon on our planet has been slowing its rotation. Therefore, days on Earth today last 24 hours. As the angular momentum of a system remains the same, it is the moon that has been moving away from us to compensate for it.
Conservation of angular momentum is important in both directions. If the moon takes more than a day to orbit, the effect will be the same as what we see here. That is, the planet's rotation slows down, and the satellite moves further away to compensate. However, if the moon rotates faster, it will produce the opposite effect: The planet's rotation will accelerate, making the days shorter, and the satellite will move even closer to compensate.
Effects of gravity on the Roche limit
To understand this, we need to know that the force of gravity gets more complicated if we get close enough. There is a point where all gravitational interactions coincide. This limit is known as the Roche limit. It is about the effect that an object has when it is supported by its own gravity. In this case, we are talking about the moon. If the moon gets so close to another object that gravity can end up deforming and destroying it. This Roche limit also applies to stars, asteroids, planets and satellites.
The exact distance depends on the mass, size, and density of both objects. For example, the Roche limit between the Earth and the Moon is 9.500 kilometers. This is taken into account by treating the Moon as a solid body. This limit means that, If our satellite were 9500 kilometers or less away, our planet's gravity would take over its own. As a consequence, the moon would be turned into a ring of fragments of material, shattering completely. The materials would continue to rotate around the Earth until they ended up falling due to the effect of gravity on the surface. These pieces of material could be called meteorites.
If a comet were within 18000 kilometers of Earth, it would be destroyed by the effects of gravity. The sun is capable of the same effect, but at a much greater distance. This is due to the size of the sun compared to our planet. The larger the size of an object, the stronger its gravitational pull. This isn't just a theory, but the destruction of satellites by their planets is something that will happen in the future. solar system. The best known example of this is that of Phobos, a satellite that is orbiting around the planet Mars and it does so at a speed faster than the planet does on its own.
Within the Roche limit, it is the gravity of the smaller object that cannot hold its own structure together. Therefore, as the object approaches the Roche limit, it is increasingly affected by the planet's gravity. When it crosses this limit, several million years from now, the satellite will become a ring of fragments orbiting Mars. Once all the fragments have been in orbit for a while, they will begin to precipitate onto the planet's surface.
Another example of an object that may be close to the Roche limit, although not as well known, is Triton, the planet's largest satellite. Neptuno. More or less it is estimated that in about 3600 billion years two things may happen as this satellite approaches the Roche limit: It may fall into the planet's atmosphere, where it will disintegrate. or it will become a set of fragments of materials similar to the ring that the planet has Saturn.
Roche's limit and humans
You might wonder: Why doesn't our planet destroy us with its gravity, given that we're within the Roche limit? While this may seem logical, there's a fairly simple answer. Gravity keeps the bodies of all living beings attached to the surface of the planet.
This effect is almost meaningless when compared to the chemical bonds that hold a body together. For example, the force that holds chemical bonds together in our bodies is much stronger than the force of gravity. In fact, gravity is one of the weakest forces in the universe. A point where gravity acts strongly would be necessary, such as in a black hole, so that the Roche limit would be able to overcome the forces that hold our bodies together.