Will the Moon escape Earth's orbit in billions of years?

In summary, the moon will continue to move away from Earth until it reaches an orbital resonance in about 50 billion years. This is due to the Earth's tidal bulges causing the moon to recede through friction. Once the Earth's rotation rate matches the moon's orbit, the moon will stabilize in a higher orbit. However, the Sun's tidal bulges will continue to slow the Earth's rotation, causing the moon to move further away. This process is complicated and not very interesting, but it is still worth learning about.
  • #1
Richard87
31
0
I've heard that the moon is very slowly moving away from Earth. Will it eventually escape Earth's orbit?
 
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  • #2
No, the moon will only move away from Earth until it reaches an orbital resonance when the length of the Earth's day and the Moon's month will be equal - that's in about 50bn years.
In theory the moon could then move closer to Earth, but since they are both going to be consumed by the sun before that - it's a bit academic.
 
  • #3
mgb_phys said:
No, the moon will only move away from Earth until it reaches an orbital resonance when the length of the Earth's day and the Moon's month will be equal - that's in about 50bn years.
In theory the moon could then move closer to Earth, but since they are both going to be consumed by the sun before that - it's a bit academic.

It would also be worth mentioning that the 50 billion years it would take for this to happen is longer than the current age of the universe.
 
  • #4
mgb_phys said:
In theory the moon could then move closer to Earth, but since they are both going to be consumed by the sun before that - it's a bit academic.
Could you please shed some light on this assertion?
You involved something like "resonance", knowing only resonance in circuits, I think about it as the time where the Moon is the farther from the Earth. But I don't understand why it would then come closer to it, considering tides effects, i.e. some "loss" of gravitational energy in detriment to friction. Feel free to correct me if I said something wrong. My goal is to learn.
 
  • #5
The Earth isn't a perfect sphere, it has bulges around the equator (and the moveable water in the oceans) this means that the moon doesn't simply go around a point. it feels a stronger pull from one side of the Earth than the other, ie from the nearer bulge.
The effect of this is to slow the Earth's spin slightly and transfer this angular momentum into the moon, which makes the moon move further away.
Eventually enough of the Earth's spin will have been transferred and the moon will have moved far enough away that it's month (it's orbit around the earth) and the Earth's rotation are the same.
At this point the bulges on each side of Earth are at the same distance and no longer have any effect.

Now any angular momentum that is lost from the system, to interactions with passing comets, or the other planets will decrease the moons distance.

ps. Orbital mechanics , especially tidal effects, are complicated and not very interesting/useful plusit's long time since I had to learn any of this junk, so someone else could probably explain it better !
 
  • #6
mgb_phys said:
The Earth isn't a perfect sphere, it has bulges around the equator (and the moveable water in the oceans) this means that the moon doesn't simply go around a point. it feels a stronger pull from one side of the Earth than the other, ie from the nearer bulge.
The effect of this is to slow the Earth's spin slightly and transfer this angular momentum into the moon, which makes the moon move further away.
Eventually enough of the Earth's spin will have been transferred and the moon will have moved far enough away that it's month (it's orbit around the earth) and the Earth's rotation are the same.
At this point the bulges on each side of Earth are at the same distance and no longer have any effect.

Now any angular momentum that is lost from the system, to interactions with passing comets, or the other planets will decrease the moons distance.

ps. Orbital mechanics , especially tidal effects, are complicated and not very interesting/useful plusit's long time since I had to learn any of this junk, so someone else could probably explain it better !
Thank you very much. I should sharpen a bit more my English. I've understood something, I just hope it's what you mean.
By the way, it might look like something uninteresting to you, but I assure you that not knowing what really happens is frustrating and makes your curiosity growing! So I don't find this uninteresting. :biggrin:
 
  • #7
fluidistic said:
By the way, it might look like something uninteresting to you, but I assure you that not knowing what really happens is frustrating and makes your curiosity growing!
The concept is interesting, it's just all the equations you have to learn, and the complications of the reference frames and which angles are measured from where, and so on that is tedious.

The wiki article on lunar orbit is a good starting point.
 
  • #8
fluidistic said:
Could you please shed some light on this assertion?
You involved something like "resonance", knowing only resonance in circuits, I think about it as the time where the Moon is the farther from the Earth. But I don't understand why it would then come closer to it, considering tides effects, i.e. some "loss" of gravitational energy in detriment to friction. Feel free to correct me if I said something wrong. My goal is to learn.

It is tidal interaction that causes the Moon to recede. The Moon raises tidal bulges on the Earth. Friction between the bulges and the rotating Earth drag the tidal bulges out of alignment with the Moon. The out of line bulges pull forward on the Moon, giving it more energy which lifts it into a higher orbit. The Earth slows its rotation in response.

This all happens because the Earth rotates faster than the Moon orbits. So when the Earth slows enough to match its rotation rate to the Moon's orbit, the situation stabilizes.

However, the Sun still raises tidal bulges on the Earth, which continue to slow the Earth's rotation. Now the Earth is rotating slower than the Moon orbits. Again, friction between the lunar tidal bulges and the Earth come into play. This time however, the bulges lag behind the Moon, pulling it backward, and into a lower orbit.

This interplay between Solar and Lunar tides will continue forcing the Moon into a lower and lower orbit.
 
  • #9
Janus said:
It is tidal interaction that causes the Moon to recede. The Moon raises tidal bulges on the Earth. Friction between the bulges and the rotating Earth drag the tidal bulges out of alignment with the Moon. The out of line bulges pull forward on the Moon, giving it more energy which lifts it into a higher orbit. The Earth slows its rotation in response.

This all happens because the Earth rotates faster than the Moon orbits. So when the Earth slows enough to match its rotation rate to the Moon's orbit, the situation stabilizes.

However, the Sun still raises tidal bulges on the Earth, which continue to slow the Earth's rotation. Now the Earth is rotating slower than the Moon orbits. Again, friction between the lunar tidal bulges and the Earth come into play. This time however, the bulges lag behind the Moon, pulling it backward, and into a lower orbit.

This interplay between Solar and Lunar tides will continue forcing the Moon into a lower and lower orbit.
Thanks. Very nice explanation, I get it.
 

Related to Will the Moon escape Earth's orbit in billions of years?

Will the Moon Escape Earth's Orbit in Billions of Years?

The interaction between the Earth and the Moon is a fascinating topic, and questions about the Moon's orbit are common. Let's explore some common questions related to whether the Moon will escape Earth's orbit in billions of years:

Q1: Is the Moon Moving Away from Earth?

Yes, the Moon is gradually moving away from Earth. This phenomenon is known as the "lunar recession." It happens due to the transfer of angular momentum from the Earth's rotation to the Moon's orbit, primarily through tidal interactions.

Q2: What Causes the Moon to Move Away from Earth?

The primary factors causing the Moon to move away from Earth are:

  • Tidal Forces: The gravitational pull of the Moon creates tidal bulges on Earth. These tidal bulges create a torque that slows down Earth's rotation and transfers angular momentum to the Moon's orbit.
  • Conservation of Angular Momentum: As Earth loses angular momentum due to tidal interactions, the Moon's orbit moves to a higher, more distant orbit to conserve angular momentum.

Q3: How Fast is the Moon Moving Away from Earth?

The Moon is receding from Earth at an average rate of approximately 3.8 centimeters (about 1.5 inches) per year. While this may seem slow, over billions of years, it can lead to significant changes in the Moon's distance from Earth.

Q4: Will the Moon Escape Earth's Orbit?

No, the Moon will not escape Earth's orbit. While it is moving away, there are limits to how far it can move. The Moon's recession will continue until it reaches a stable position known as the "lunar synchronous orbit" or "tidal locking." In this orbit, the Moon will always keep the same face toward Earth, and its recession will cease.

Q5: What Is the Future of the Moon's Orbit?

In the distant future, the Moon will reach a stable orbit where it will no longer move away from Earth. At that point, the Earth and Moon will be tidally locked, and the Moon's rotation will match its orbital period. This means we will always see the same side of the Moon from Earth.

In summary, while the Moon is currently moving away from Earth, it will not escape Earth's orbit. Instead, it will reach a stable position where its recession will cease, and it will become tidally locked with Earth.

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