Harbringer
Your A One Flower Garden
What would be the effects of the moon moving closer to the earth, like say 100 miles, or one thousand miles?
What would happen if the moon moved closer?
- Thread starter Harbringer
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warpus
Sommerswerd asked me to change this
The first effect I can think of is the tides would become a lot stronger. This would affect a whole bunch of stuff.
No. It would just go on an elliptical trajectory. Conservation of angular momentum means that to crash the moon into the earth you need to bring them very close (or destroy almost all angular momentum) so that the trajectory of the moon intersects the earth.
Despite some popular opinions, that it would only require small disturbances to send a moon or planet into a death spiral, this is actually impossible without massive energy transfer.
Perfection
The Great Head.
Well even if you have a large disturbance you won't get a death spiral.
Ouch. Thanks for correcting me though.Leifmk
Deity
The closest you can get is if you make the orbit eccentric enough that it encounters significant (on a relevant timescale) drag from the primary's upper atmosphere during the closest approach. Then the orbiting body will gradually lose momentum and energy on every orbit and eventually experience terminal aerobraking/lithobraking.
Still won't be a spiral trajectory, mind you. And yes, for something orbiting far out (like the Moon around the Earth, or even something in geosynchronous orbit) the energy required for such a change is rather a lot per unit mass; not so much for something that's already in a low orbit (like the ISS).
That would not work. The moon is has much more weight than the earths athmosphere. The moon would break apart because of the inhomogenous gravitation long before it lost any measurable part of its momentum.
Perfection
The Great Head.
As Gigaz notes, it really doesn't matter, if the Moon was that close, tidal forces would rip it to shreds anyways.
Leifmk
Deity
By this point in the thread we were clearly no longer talking specifically about the moon orbiting the earth but about any orbiting body about a planet, or whatever.
Case in point: Low-orbiting satellites actually do experience very slow aerobraking, and will not remain stable in the long run.
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