If the moon exploded...

Factual Questions
1

Just read an article which that Saturn’s rings may have been caused by a moon that was fractured in a collision. If the same thing happend to our moon, what would be the effects on earth? No tides, for starters, I would guess. I would guess without tides, we’d see some massive ocean extictions. Would the change from one large mass to a spread out ring affect the earth’s rotation appreciably? Would the collision itself cause earthquakes? Any other changes?

(I, of course, realize that any answers will be somewhat speculative :slight_smile: )

2

Can’t happen. The total mass of Saturn’s rings is only about 1% the mass of the Moon. There are comets around that could break up a moon that size- there just aren’t any around near Earth that could break up the Moon, as far as we know.

3

The Master Speaks:

http://www.straightdope.com/columns/001027.html

4

[QUOTE=Anne Neville]
Can’t happen.
[/QUOTE]

That doesn’t change the fact that it’s an interesting, hypothetical question.

The earth’s rotation would change since the earth and the moon (minus other bodies) rotate around their common center of mass. If the moon turned into a ring, that center would move to the center of the earth. This would “move” the earth, somehow.

5

[QUOTE=tremorviolet]
Just read an article which that Saturn’s rings may have been caused by a moon that was fractured in a collision. If the same thing happend to our moon, what would be the effects on earth? No tides, for starters, I would guess.
[/quote]
Lunar tides would go away, but small solar tides would remain. There would be a high tide at noon and midnight, and low tides at sunset and sunrise.

Interesting question! I hope a biologist can answer it!

No, I don’t think so. It would, however, stop the ongoing slowing of the Earth’s rotation rate.

I don’t really think so, though this depends on the exact event that disrupted the Moon. We are talking about a very large object, after all. It would take time for its mass to spread out appreciably. As it did so, the tidal forces would slowly abate, and the Earth’s figure would slowly relax and the planet would become more spherical. Maybe a geologist would know whether the change would be drastic enough to trigger significant earthquakes, but I doubt it, because IIRC, the size of the Earth’s solid tidal bulge is significantly less than a meter–and that gets dragged around the Earth once every day without causing the end of civilization.

Depending on how violent the disruption was, some debris might hit the Earth. It could be bad if big chunks (10 km or so in diameter) hit us–as bad as an asteroid impact a la the K-T impact that killed the dinosaurs. Assuming that doesn’t happen, though, in the long term, very small pieces of dust would continually filter in due to Poynting-Robertson drag and hit our atmosphere, creating rather pretty meteoritic shows, particularly over the equatorial regions. This could also cause weather problems–there is a band of aerosols over Saturn’s equator.

The ring would start out thick, but would eventually settle down into the Earth’s equator plane. It wouldn’t have the pretty structure of Saturn’s rings, because those are caused by the gravitational influence of Saturn’s moons.

Eventually, the Moon would reaccrete, but that would take . . . um . . . rough estimate . . . hundreds of thousands of years. (Don’t hold me to that figure.) In the meantime, the ring would look like an arc, rainbow-shaped, in the southern sky for northern hemisphere observers, and in the northern sky for southern hemisphere observers. Actually, for most of the year it would look like horns at night, because the Earth’s shadow will fall across it. Whethe it was visible in the daytime would depend on how finely most of the Moon was crushed, and how much its mass was spread out.

Remember, though, that the entire mass of Saturn’s rings can be accounted for by a moon 100-200 km across, only about 3% of the Moon’s diameter! It would take an extraordinary event to destroy a 100 km moon, but to destroy the Moon, basically, you have to invoke Little Green Men, or a black hole wandering through the Solar System, or some other improbable cataclysm.

6

[QUOTE=This space intentionally blank]

The earth’s rotation would change since the earth and the moon (minus other bodies) rotate around their common center of mass. If the moon turned into a ring, that center would move to the center of the earth. This would “move” the earth, somehow.
[/QUOTE]
Good point. Like the relaxation of the Earth’s figure, though, I think this would be a fairly gradual change as the Moon’s material dispersed from a clump into a ring. The Earth’s wobble due to the Moon is currently something like 4500 km, and that would gradually reduce to zero.

7

[QUOTE=Podkayne]
Actually, for most of the year it would look like horns at night, because the Earth’s shadow will fall across it.
[/QUOTE]
Hmmm, I doubt the size of the gap in the “horns”, or else we’d have a lot more lunar eclipses than we do now. The distance from the moon to the earth is 239,000 miles, whereas the diameter of the earth is 8,000 miles, so even given perfect conditions the gap will only take up 1/30th of the sky.

8

[QUOTE=Ludovic]
Hmmm, I doubt the size of the gap in the “horns”, or else we’d have a lot more lunar eclipses than we do now. The distance from the moon to the earth is 239,000 miles, whereas the diameter of the earth is 8,000 miles, so even given perfect conditions the gap will only take up 1/30th of the sky.
[/QUOTE]
The with of the Earth’s penumbra (the fuzzy part of the shadow) at the orbit of the Moon is about 16,000 km, or about 4-5 times the width of the Moon, so that would be the width of the gap on the equinoxes. You’re right, the gap would not be very large, but the arc of the rings would be broken.

Speaking of equinoxes, the rings would look different in the summer and in the winter. Whether they would be brighter or dimmer would depend, again, on how finely the Moon is pulverized. If the particles were large, they would be dimmer in the wintertime.

9

… free cheese for everyone!!!

10

If the moon gets blasted apart, a small portion of those bits are going to hit the earth. The resulting effect on the biosphere would make the Permian extinction look like a footnote. I’d be surprised if much beyond bacteria and deep sea vent organisms were left.

11

I’m also not sure you could blow the Moon into a ring, without significantly lowering its orbit. Any Moon-bits outside of the Roche limit would tend to re-coalesce, rather than spreading out into a ring. So the ring would be composed only of those parts which ended up below the Roche limit, and would in fact have a significant shadow-gap.

12

[QUOTE=Lemur866]
If the moon gets blasted apart, a small portion of those bits are going to hit the earth. The resulting effect on the biosphere would make the Permian extinction look like a footnote. I’d be surprised if much beyond bacteria and deep sea vent organisms were left.
[/QUOTE]

I think we have a winner here, folks! For the record, the end-Permian extinction, which occurred circa 250 million years ago, resulted in the loss of 57% of all known families and 83% of all known genera (compared to 17% of all families and 50% of all genera for the K-T extinction). But let’s assume for the moment that somehow (a miracle occurs, Jack O’Neill finds a way to activate an Ancient planetary shield), the Earth avoids getting smacked by anything significant.

[QUOTE=tremorviolet]
I would guess without tides, we’d see some massive ocean extictions.
[/QUOTE]

It’s unlikely to be as bad as you might think. Yes, there are some creatures that do depend on tides and/or intertidal zones on the coast for food and reproduction (sometimes in ways that we don’t fully understand), and you’d expect these to suffer. However, the bulk of marine life lives away from the shoreline, and isn’t influenced by tides at all. Moreover, there are plenty of places on Earth right now where the tidal range (height difference between low tide and high tide levels) is less than a meter… dampening the tide further isn’t going to matter much in those microtidal zones.

We would indeed still have high and low solar tides, but no more spring or neap tides.

[QUOTE=Podkayne]

[QUOTE=tremorviolet]
Would the collision itself cause earthquakes?
[/QUOTE]

I don’t really think so, though this depends on the exact event that disrupted the Moon. We are talking about a very large object, after all. It would take time for its mass to spread out appreciably. As it did so, the tidal forces would slowly abate, and the Earth’s figure would slowly relax and the planet would become more spherical. Maybe a geologist would know whether the change would be drastic enough to trigger significant earthquakes, but I doubt it, because IIRC, the size of the Earth’s solid tidal bulge is significantly less than a meter–and that gets dragged around the Earth once every day without causing the end of civilization.
[/QUOTE]

I would not expect there to be any significant change in earthquake frequencies based solely on the redistribution of the Moon’s mass into a ring. As Podkayne mentions, the solid Earth tide is pretty small already, so you wouldn’t see a huge drastic change in the shape of the Earth.

There’s been some speculation that a ring of debris circling the Earth’s equator could force a significant climatic change by cutting down the amount of incoming solar radiation in the tropics. (Since the tropics are the “heat engine” that drives Earth’s climate, reducing the amount of incoming energy there, as opposed to mid- or high latitudes, should have a major cooling effect.) It’s an interesting idea that resurfaces every few years in a variety of contexts (most recently as an antidote to global warming). The hypothesis hasn’t gained a lot of traction just yet, though, because frequently there is not enough corraborative evidence to support a meteorite impact as the source of enough debris to create a sufficiently long-lived ring.

13

An late idiot named Smbat (pronounced shim-pot, he later changed it to Alexander) Abian seriously proposed sending a couple nukes to blow up the moon for the purpose of creating a ring that would light up the night time sky. Leaving aside the sheer idiocy of the idea, it is not so easy to blow up a body the size of the moon. It is not so easy to blow up an asteroid a mile in diameter with a nuke, so how are you going to do it one that is 2000 miles in diameter and presumably with 8 billion times the mass.

I had the misfortune of having taken a course taught by Abian long before this. Truly one of the demented. He also took an exercise I solved and published it under his name.

14

[QUOTE=Hari Seldon]
An late idiot named Smbat (pronounced shim-pot, he later changed it to Alexander) Abian seriously proposed sending a couple nukes to blow up the moon for the purpose of creating a ring that would light up the night time sky. Leaving aside the sheer idiocy of the idea, it is not so easy to blow up a body the size of the moon. It is not so easy to blow up an asteroid a mile in diameter with a nuke, so how are you going to do it one that is 2000 miles in diameter and presumably with 8 billion times the mass.
[/QUOTE]

Ahh, the source of inspiration for Armageddon is now clear. :smiley:

15

Werewolves would just have a constant low-level hairiness.

16

What would Al Gore be first emperor of?

17

[QUOTE=Hari Seldon]
I had the misfortune of having taken a course taught by Abian long before this. Truly one of the demented. He also took an exercise I solved and published it under his name.
[/QUOTE]

Oy. I was one of the many who had a futile go at him on Usenet way back in the day. He was going on about how Earth was in an ‘evil orbit’ and only by blowing up the Moon could we avoid all sorts of disasters, plagues, wars, etc. I’d never heard about his ring idea.

Maybe, in the end, he just wanted to blow up the Moon cause it would be cool to watch. :shrug:

18

These guys want to move the Earth’s orbit with a big asteroid! It doesn’t say what plans they’d have for the Moon.

We need the Moon! It keeps the Earth’s tilt axis stable, and without it the resulting wobbles and climate swings would have big consequenses for the evolution of life. Here’s other Earth-Moon interactions, from Astronomy Today.

19

[QUOTE=Podkayne]
The with of the Earth’s penumbra (the fuzzy part of the shadow) at the orbit of the Moon is about 16,000 km, or about 4-5 times the width of the Moon, so that would be the width of the gap on the equinoxes. You’re right, the gap would not be very large, but the arc of the rings would be broken.

[/QUOTE]

Eh, penumbra. Who even notices when the Moon goes into Earth’s penumbra? Might dim an arc of the ring a mite, but nothing spectacular.

20

This all assumes that the Moon would be blown up and the residue remain in orbit, and not knocked out of its orbit (who else is old enough to remember Space:1999?) towards the sun. What kid of megaton billiard ballistics would that require?