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Author Topic: If Earth is gaining mass, why is the Moon drifiting away?  (Read 3964 times)

Johann Mahne

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Johann Mahne  asked the Naked Scientists:
   Dear Chris,
I often try to get through to you on 702, but no luck .... you are too popular.
 I also send sms (text) messages but they are always rejected.
So now I need to ask this directly!

I assume that the Earth is getting heavier over time, due to impacts with objects in space.

So why then is the moon moving away from us?

Cold here, but sunny on the highveld.
Hope you're enjoying that British weather..

Cheers
Johan
What do you think?
« Last Edit: 18/07/2010 16:30:02 by _system »


 

Offline Soul Surfer

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #1 on: 19/07/2010 00:26:24 »
The moon is moving away from the earth because the tidal friction of the lunar tides on the earth is lowing down the rotation of the earth and this in its turn (because the earth is rotating faster than it takes the moon to orbit the earth) is feeding energy into the moons orbit which causes it to move to a slightly higher orbit (and counterintuitively to slow down)
 

Johann Mahne

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #2 on: 22/07/2010 09:06:58 »
Seems a plausable answer.If the rotation of the earth exactly matches the orbit of the moon, would we hold on to our dear moon?
I'm gonna miss that moon...
 

Offline Eric A. Taylor

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #3 on: 22/07/2010 11:24:14 »
First the Earth is gaining an extremely small about of mass compared to it mass now. The Earth gains only a few hundred tons of mass each year, but the Earth already weighs 5.974224 Kg. Even if Earth gains 5 million tons of matter a year that is only 10-17% At this rate it will take Earth 1018 years to gain 1% of it's current mass. By this time every star in the universe will have used up all of the available hydrogen, thus no more stars. All of the white dwarfs will be long cooled to nearly 0K. The universe will be cold dark and dead.
« Last Edit: 22/07/2010 11:35:04 by Eric A. Taylor »
 

Offline Eric A. Taylor

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #4 on: 22/07/2010 11:33:20 »
Seems a plausable answer.If the rotation of the earth exactly matches the orbit of the moon, would we hold on to our dear moon?
I'm gonna miss that moon...

There is not enough angular momentum in Earth for the moon to achieve escape velocity, so Earth is going to keep it's moon a long long time (possibly forever.) Once the Earth is tidally locked to the moon it will no longer be getting farther away. However this will take over 1 trillion years. However in about 5 billion years (about 5% of the time required for tidal lock). The sun will be dead
 

Johann Mahne

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #5 on: 23/07/2010 13:28:35 »
That could be true,since I've just worked out that the gain in distance is about 10 nano percent per year.
Which is a lot more than the gain in mass ( that is if you are right that all those asteroids are relatively small fellows).


 How could a small ratio like this be accurately measured?Sounds like science fiction.....?


 

Offline Eric A. Taylor

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #6 on: 23/07/2010 19:02:25 »
We know the average density of material in the area around Earth, thus the amount of stuff we run into every year. I'm not sure what the number is though. Every time you see a shooting star the Earth has gained the mass of a single grain of sand.

Humans have also REDUCED Earth's mass. The sum mass of all the space probes that have been blasted out of Earth orbit. (Any object in Earth's orbit still contributes to Earth's mass)
 

Johann Mahne

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #7 on: 23/07/2010 19:49:57 »
I was actually referring to the moon distance?
 

Offline Eric A. Taylor

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #8 on: 26/07/2010 06:02:29 »
The moon is moving away because it's robbing momentum from Earth's spin. Each day is a little longer than the day before.

 

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If Earth is gaining mass, why is the Moon drifiting away?
« Reply #8 on: 26/07/2010 06:02:29 »

 

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