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Our moon has been slowly drifting away from Earth over the past 2.5B yrs

phys.org

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Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#5

Post by londons_explore »

hinkley wrote: post #2

Would Pangea have resulted in less tidal locking due to less resistance to the flow of the oceans? I would think ice ages also slowed things down.

I would suspect the effect of tidal forces in the rock of the earth has more impact than in the seawater.

Simply because there is a lot more rock, and as molten magma deforms it absorbs a lot of energy - it has a pretty high viscosity.

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#6

Post by elevaet »

> We found that the moon was around 60,000 kilometers closer to the Earth then [2.46 billion years ago] (that distance is about 1.5 times the circumference of Earth). This would make the length of a day much shorter than it is now, at roughly 17 hours rather than the current 24 hours.

I wish they explained why the moon being that much closer would have such a dramatic effect on the day length. Can someone explain this? Seems off to me, but I'm very physics-naive.

Also, good to know it's drifting away, and not towards the earth!

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#8

Post by mgraczyk »

elevaet wrote: post #6

> We found that the moon was around 60,000 kilometers closer to the Earth then [2.46 billion years ago] (that distance is about 1.5 times the circumference of Earth). This would make the length of a day much shorter than it is now, at roughly 17 hours rather than the current 24 hours. I wish they explained why the moon being that much closer would have such a dramatic effect on the day length. Can someone explain thi…

To first order I think the explanation is just conversation of angular momentum. The moon earth system has to have it's angular momentum constant over time. If the moon is further away in a stable orbit, the earth must rotate slower.

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#9

Post by morsch »

elevaet wrote: post #6

> We found that the moon was around 60,000 kilometers closer to the Earth then [2.46 billion years ago] (that distance is about 1.5 times the circumference of Earth). This would make the length of a day much shorter than it is now, at roughly 17 hours rather than the current 24 hours. I wish they explained why the moon being that much closer would have such a dramatic effect on the day length. Can someone explain thi…

It's explained here: https://en.m.wikipedia.org/wiki/Tidal_acceleration

Re: Our moon has been slowly drifting away from Earth over the past 2.5B yrs

#10

Post by FiatLuxDave »

elevaet wrote: post #6

> We found that the moon was around 60,000 kilometers closer to the Earth then [2.46 billion years ago] (that distance is about 1.5 times the circumference of Earth). This would make the length of a day much shorter than it is now, at roughly 17 hours rather than the current 24 hours. I wish they explained why the moon being that much closer would have such a dramatic effect on the day length. Can someone explain thi…

Sure. The earth is spinning faster than the the moon is going around the earth (earth rotates in one day, the moon goes around in about a month). When the tides transfer energy and momentum to the moon from the earth's spin, it slows down the earth's spin and gives the moon more energy. This moves the moon to a higher orbit, so it moves a bit farther away from us. The source of energy for the whole process is the earth's spin. It takes a lot of energy to lift a moon, relative to the amount of energy in the earth's spin, which is why it has such a dramatic effect on the day length.
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