Is the moon spinning off into space? Would it be better nearer or further away?

[Lancer]

I watched a show a while back about the early Earth and the beginning of life. In it there was a quick mention of how the moon used to be closer to the earth, creating greater tidal effects. So, the moon is moving away from the Earth. (Just remembered that it's not spinning)

Is that a good thing? Sure, eventually it might go wandering off, fall into the sun or set itself up as a planet on the same plane as the Earth. That would be a bummer. Before it wanders off its gravitational effect would become less. That means less tidal effect, smaller waves, perhaps less earthquakes?

Would that be good? Is the optimum distance from the earth still to come or come and gone?

[MichaeltheGreat]

We'll probably do the job first, but before the sun goes red giant and vaporizes us, the moon will kill us all off, since it's tidal locking us faster than it's going away.

[Lancer]

What's "tidal locking" Mike?

[Lancer]

.

[Nacht]

Well considering that most major environmental changes are bad for the more advanced species, I think it would be better for us humans if the moon just stays where it is.

[Ben Kenobi]

You pulled 'tidal locking' right outa your ass you yankee gringo you!

(Just remembered that it's not spinning)

Lancer, you have referred to the phenomenon of tidal locking. The reason the moon no longer spins is because the Earth has tidally locked the moon so that one side always faces the Earth.

The moon also slows down the Earth's rotation, but because the Earth is quite a bit more massive, the tidal locking takes much more longer.

I want to see MtGs calculations that show the moon tidally locking the Earth faster than the moon will drift away from the Earth.

Remember, you have to take into account, that as the moon moves farther away, there will be less tidal friction, and the earth will slow down less quickly.

[Lancer]

Sounds like the days will keep getting longer... There ought to be 2 habitable bands around the edges of a locked earth though?

[Dauphin]

Originally posted by obiwan18

I want to see MtGs calculations that show the moon tidally locking the Earth faster than the moon will drift away from the Earth.

Remember, you have to take into account, that as the moon moves farther away, there will be less tidal friction, and the earth will slow down less quickly.

The Moon gains the energy to move to a higher orbit by taking it from the Earth's rotational energy. Simply conservation of angular momentum and energy. I'm not sure how much effect friction of oceans has on the dynamics though.

The Earth-Moon orbit coupling will be complete when an Earth day is as long as a Lunar month. I seem to recall that would be 56 days long (this may be way off though). If the Moon can have a stable orbit with that rotation period, which I'd imagine it can, then we won't lose the Moon.

If we did lose the Moon for whatever reason there would be more wobbling of the Earth's rotational axis, leading to extreme climate variations.

[MichaeltheGreat]

Originally posted by Lancer
Sounds like the days will keep getting longer... There ought to be 2 habitable bands around the edges of a locked earth though?

There's two places the energy goes from the braking of the earth's rotation - one is change in the moon's orbital distance, the other is heat here on the earth. Unless you like hot steam baths, earth won't be a nice place. This is something on the order of hundreds of millions to a billion years, though, so I'm sure if people haven't killed each other off, we'll have done something else to each other.

Obiwan - any pair of rotating objects in which one orbits the other will tidally lock each other eventually (the operative word here), as a consequence of conservation laws. While they're rotating at different angular rates from the revolution, there is a tidal locking effect. AFAIK, the only ways out of that situation is if there's an unstable orbit due to interactions with other objects, or if one of the objects changes do to collisions, stellar evolution, or what have you.

Tidal locking is fairly common - Mercury is locked to the sun, at IIRC a couple of the Galilean moons are already locked to Jupiter, and there should be a few more, but I don't know how much research work has gone into tracking the rotational periods of minor satellites in our solar system. I suspect not much, since there's not a lot of observational data.

The more massive object locks the less massive object first, but the relationship is fairly complex. It has to address sums and differences in vectors, so you need to account for not only mass but diameter, as well as distance. So if you've got two black holes, with diameters of a few centimeters, you have to be patient.

Mercury would not lock the sun (ignoring the sun's evolution, which would happen beforehand anyway) since it's internally driven convection contributes far more to the sun's internal motion that does Mercury's rather tiny mass and net difference of tidal gravitational vectors.

With the earth-moon pair, the earth's core convection doesn't count much, if at all, because it's not primarily an internally driven process. The relative masses, distance and diameters are close enough between earth and moon that both objects are likely to survive undisturbed long enough for mutual tidal locking to occur.

[Cruddy]

Originally posted by Nacht
Well considering that most major environmental changes are bad for the more advanced species, I think it would be better for us humans if the moon just stays where it is.

I agree, to the extent that if it isn't broken why fix it - but I think we are better off having an understanding of how the system works just in case it needs a kick in the right direction.

[Guest]

Yes
The moon would eventually tidal lock the Earth is true.
But I seem to recall that the the timeframe was very long, even in astronomical terms....

[MichaeltheGreat]

The shortest estimate I've seen is ~350 million years, assuming a fairly simple model of the earth's interior. (The inner core is rotating faster than the the mantle & surface already, due to internal convection and the amount of tidal braking that has occurred so far.

[Az]

This would just mean that the earth will have 30*24 hour long days, not that it will completely stop.

[Jaguar]

Originally posted by MichaeltheGreat
We'll probably do the job first, but before the sun goes red giant and vaporizes us, the moon will kill us all off, since it's tidal locking us faster than it's going away.

For some reason I find that sad. We're gonna have to kill our own moon in self defense.

[Az]

Kid, if we want to survive, we've got to think big.

I say, chop the moon off, and build asteroid sized spaceships.