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What if the moon disappeared?

shadron

Philosopher
shadron
Joined
Sep 2, 2005
Messages
5,918
A new episode of the History channel's Universe series: What would happen if the moon disappeared? Seems ironic, given the recent thread on what would happen if the moon doubled in size.

According to the show, two things mainly:

The tides held by the moon would run off, causing "powerful pulses" with up to 50' tsunamis on almost all coasts. The moons tide water would run off to the sun's tides, making a very bad situation if the moon were at first or third quarter.

Secondly, the earth would loose it's precessional axis. Right now the axis presesses and nutates, but within small bounds. Without the moon to stabilize the oblate bulge, the axis could easily move and point in any direction (over, say, 100,000 years time).

Personally, I believe the latter, but I'm having some trouble with the former. The solar and lunar tides are independant systems; if one disappeared, the other would go on independently. The sun would not "take control". The 1 meter bulge at the former pode and antipode would slosh down towards the larger -1/3 meter middle ground, and while a huge amount of water would be sloshing, the deep ocean height would not exceed the 1 meter initial height. There'd be no leading edge of the tsunami, and I doubt the piling-up effect would cause any 16 meter wave. I think the writers were searching for a starting conclusion, and talked the two talking heads, Dana McKenzie (auther of The Big Splat) and the Griffith Observatory spokesperson Laura Daney, neither definitely a scientists AFAIK.

See the first 10 minutes here:



How say ye'all?
 
Yup, the moon stabilizes Earth's axis. Without it the axis would wander, due to the non-rigid nature of Earth.

Tides would get smaller, becoming dominated by Sun's gravity. At a guess they'd become whatever the current difference between spring and neap tides is.
 
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I've also heard - but have not even considered verifying - that the moon's gravity helps keep the Earth's molten iron core spinning. If that is true, would removing the moon mean the core would slow its spin and the magnetic field would weaken and not protect as much from solar winds?

(ETA: if its a real consequence, I imagine the time scale would be pretty broad - millions of years?)
 
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MY only complaint is people do the mental manipulation from Might happen to Going to happen :(
 
hmm, do you think the history channel is starting to get their ideas from JREF?
 
firecoins said:
last night, there was no moonn! OMG! Where did it go?
Click to expand...

Don't laugh. I was at the beach two weeks ago, walking on the beach on a moonless night with my wife. She remarked on how the sky was FILLED with stars.. and.. why is the moon not out? WHERE IS THE MOON, HONEY?! ITS NOWHERE - NOT EVEN A LITTLE SLIVER!

OK, go ahead and laugh - I sure did.
 
Careyp74 said:
hmm, do you think the history channel is starting to get their ideas from JREF?
Click to expand...

I wondered about it :). "...and I never, never watch TV, (What, never? No, never. What, never? Well, hardly ever)", so I have to wait until the other parts come out on youtube before I can comment on them, but I thought that this was so egregious that I have to just get it stated, and get some other opinions. Perhaps if they did get their ideas here they would be one up.

As for the second problem, without the moon the Earth's axis will move rather more wildly than it does now. Their own talking head says the extremes would be seen on the order of "hundreds of thousands of years", and then goes on to wonder if the human race is adaptable enough to work with that. As we are learning to control technology, and given what we've accomplished in the last 2,000 years, I'd say its likely. Much less likely is whether we can control our own selves long enough to last several hundred thousand years. Our basic problem with climate control in our current age is not it's magnitude or direction, but it's speed. As Napolean said, "Ask me for anything but time."

I hear later on in this video episode they talk about the 50 billion years it will take for the moon to quit moving outwards in its orbit, only they say at that point the Earth will loose the moon gravitationally. Everything I've heard is that it will achieve Earth lock and quit moving outwards. And I notice that none of their talking heads seem to have doctorates. Perhaps thay're trying to do the series under tighter budget constraints. Interesting.
 
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madurobob said:
Don't laugh. I was at the beach two weeks ago, walking on the beach on a moonless night with my wife. She remarked on how the sky was FILLED with stars.. and.. why is the moon not out? WHERE IS THE MOON, HONEY?! ITS NOWHERE - NOT EVEN A LITTLE SLIVER!

OK, go ahead and laugh - I sure did.
Click to expand...

Yeah, and after spending a week on the couch...
 
madurobob said:
I've also heard - but have not even considered verifying - that the moon's gravity helps keep the Earth's molten iron core spinning. If that is true, would removing the moon mean the core would slow its spin and the magnetic field would weaken and not protect as much from solar winds?

(ETA: if its a real consequence, I imagine the time scale would be pretty broad - millions of years?)
Click to expand...
Yes thats what happened to Mars.
 
I think this sort of question is meaningless without any understanding of the process by which the moon suddenly ceases to exist. If it just is there one moment and isn't the next, then the law of conservation of mass-energy has gone with it, and even 50' tsunamis on all coasts is pretty small beer compared to the fact that we can never again make any valid predictions whatsoever about any feature of the physical universe. If it's blown to small fragments, then the mass is still there, and there will be some transition between the initial state, of a single compact mass, and the final state, of a whole load of small rocks spread out to a radius greater than the moon's current orbit, which in themselves could be as interesting to study as the nature of the final state. If it's pulled away intact, how fast does it move? It's no longer a sudden change, so there's time for the system to react. It's impossible to make predictions until you've got some idea of the process involved.

Dave
 
Cainkane1 said:
Yes thats what happened to Mars.
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Really? Mars has pretty tiny moons, doesn't it?

Oh - or are you saying that the core stopped spinning at some point in the past, not related to its small moons, and that's why there is now so little atmosphere? Interesting, I had no idea.
 
When the moon leaves the sky,
and we're all gonna die...

That's our morte'
 
madurobob said:
I've also heard - but have not even considered verifying - that the moon's gravity helps keep the Earth's molten iron core spinning.
Click to expand...

That is incorrect. First, the core is solid. Second, the earth's core rotates slightly faster than the crust. The moon's gravity is acting to slow down the crust (through tides), and hence is putting a small frictional drag on the core.
 
Ziggurat said:
That is incorrect. First, the core is solid. Second, the earth's core rotates slightly faster than the crust. The moon's gravity is acting to slow down the crust (through tides), and hence is putting a small frictional drag on the core.
Click to expand...

OK, right - solid core spinning in a liquid outer core. I knew that, just didn't spell it out correctly.

So, the moon is our enemy - working to eliminate our magnetic field?

Run for your lives!
 
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