So the Moon split...

[Blackhawk748]

We see this in a variety of properties, RWBY is probably the most recent but the idea came to me from rewatching Thundarr the Barbarian. For them, it apparently split in half from a rogue planet passing in between it and Earth.

Spoiler: Pic

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Now, Im not certain if the moons own gravity would be enough to keep these two pieces together, but what I am intensely curious about is what would happen if the moon split in two or more pieces on our end. Would this royally mess with the tides? Would it just get chucked out of orbit?

[Squire Doodad]

I mean, a lot of it depends on how the split happens and the subsequent movement of the halves.
The debris can get stuck and become a ring, or merely burn up in the atmosphere.

It can also cause a shower of meteors, and if you've really messed up and somehow made it so the moon itself is headed towards the surface, doom quite a few people!

[Eldan]

There's a book called Seveneves by Neal Stephenson where something very much like this happens.

Spoilers: everyone dies.

Those small chunks you see flying away there to the side? Some of them would eventually hit Earth and kill everyone.
Now, if you had relatively clean halves like in that picture, and they styed relatively close together, they would be inside each other's Roche limit. This limits how close together two bodies can be before they rip each other apart by gravity. And they'd be very far inside. It's not possible for two massive bodies to be that close and just stay next to each other.

So, those neat halves would be ripped apart into smaller chunks, which would start impacting each other, heat up from the gravity and the impacts, melt, and eventually reform into the moon again. Just one that would be quite a bit hotter for a long while. However, in the process, more chunks would be ejected out of the new moon swarm, most of which would also hit the Earth.

The effect would be somewhat similar to the Heavy Bombardment, and likely entirely sterilize the Earth's surface, or at least much of it.

[Blackhawk748]

There's a book called Seveneves by Neal Stephenson where something very much like this happens.

Spoilers: everyone dies.

Those small chunks you see flying away there to the side? Some of them would eventually hit Earth and kill everyone.
Now, if you had relatively clean halves like in that picture, and they styed relatively close together, they would be inside each other's Roche limit. This limits how close together two bodies can be before they rip each other apart by gravity. And they'd be very far inside. It's not possible for two massive bodies to be that close and just stay next to each other.

So, those neat halves would be ripped apart into smaller chunks, which would start impacting each other, heat up from the gravity and the impacts, melt, and eventually reform into the moon again. Just one that would be quite a bit hotter for a long while. However, in the process, more chunks would be ejected out of the new moon swarm, most of which would also hit the Earth.

The effect would be somewhat similar to the Heavy Bombardment, and likely entirely sterilize the Earth's surface, or at least much of it.

That would certainly explain how Thundarr Earth looks the way it does. After the rogue planet messed up the atmosphere, a rain of moon chunks probably screwed up what population was left.

So ya, not pleasant.

[Eldan]

And that's still the "nice" version. In Seveneves, the eventual bombardment and melting of the moon is intensive enough that it heats the Earth's atmosphere to a glow. The planet is cooked.

[halfeye]

We see this in a variety of properties, RWBY is probably the most recent but the idea came to me from rewatching Thundarr the Barbarian. For them, it apparently split in half from a rogue planet passing in between it and Earth.

...

Now, Im not certain if the moons own gravity would be enough to keep these two pieces together, but what I am intensely curious about is what would happen if the moon split in two or more pieces on our end. Would this royally mess with the tides? Would it just get chucked out of orbit?

A rogue planet passing between the moon and Earth? that's very improbable.

Obviously it's fiction so anything goes, but it's fiction so Anything Goes.

A planet passing close enough to the moon to do that to it would probably take one half of the remains of the moon into orbit around itself. A planet passing close enough to the moon to do that would probably perturb the Earth's orbit around the sun. If the bits didn't fall into something else, they would perhaps fall back together, but the big bits would almost certainly become round due to their own gravity.

That planet in Tachyon with a chunk of itself hanging above a hole? could never happen without much more fancy anti-gravity than otherwise showed up in the game.

[Blackhawk748]

A rogue planet passing between the moon and Earth? that's very improbable.

Obviously it's fiction so anything goes, but it's fiction so Anything Goes.

A planet passing close enough to the moon to do that to it would probably take one half of the remains of the moon into orbit around itself. A planet passing close enough to the moon to do that would probably perturb the Earth's orbit around the sun. If the bits didn't fall into something else, they would perhaps fall back together, but the big bits would almost certainly become round due to their own gravity.

That planet in Tachyon with a chunk of itself hanging above a hole? could never happen without much more fancy anti-gravity than otherwise showed up in the game.

That's what the show calls it, if call it a large comet considering it's smaller than our moon. Either way it's a rough time in that universe

[halfeye]

That's what the show calls it, if call it a large comet considering it's smaller than our moon. Either way it's a rough time in that universe

If it was less massive than the moon, it would split before the moon did.

[Jay R]

Whatever did that to the moon would hurt the earth far more than the change to the moon would.

Without knowing what it was, I can't get specific about its effects.

In any case, we wouldn't be around to see it.

[halfeye]

If it was less massive than the moon, it would split before the moon did.

Whatever did that to the moon would hurt the earth far more than the change to the moon would.

Without knowing what it was, I can't get specific about its effects.

In any case, we wouldn't be around to see it.

It is just complete nonsense by the sounds of it.

[Blackhawk748]

It is just complete nonsense by the sounds of it.

Is an 80s cartoon about a Magical Post Apocalyptic Earth. Its all about the aesthetics and adventure not realistic world building.

I was just curious about what a cracked moon would do.

[LibraryOgre]

Ah, man, ee chee wa maa. Short answer: Pritka pritka.

This is, of course, partially in Ewok, as Endor dealt with a moon blowing up.

[BaronOfHell]

Sorry if this is off topic, but to me, the moon in the picture looks more like it has a huge canyon than it is splitted in two.
With huge I mean broad, not deep. I imagine the lack of light reflected from the canyon means it could be shallow.

[Blackhawk748]

Sorry if this is off topic, but to me, the moon in the picture looks more like it has a huge canyon than it is splitted in two.
With huge I mean broad, not deep. I imagine the lack of light reflected from the canyon means it could be shallow.

There are a few scenes in the show where it looks like its still connected and only split like halfway, so that's a possibility.

[Jimorian]

At the scale of bodies like the Moon or Earth, everything has the "strength" of a liquid. While you might get the picture in the OP immediately in the aftermath of whatever object passed through the system, within days the whole thing would be a sphere again, with whatever needs melting to achieve that getting melted. And all that debris around it, if it hasn't already escaped the moon's overall gravity well, or in the narrow band of probability of being in actual orbit, it's going to be part of that process.

[Cikomyr2]

I remember a comic i read at one point where a faction developped a weird transdimentional power and were able to produce a beam of any lenght that would cleanly cut in half anything it touched.

The first result we see of it was that they had cut Jupiter in half. We clearly see in the comic the GAS GIANT cut in two clean halves.

I was so pissed at the stupidity i refused to keep reading for about 2 weeks.

Then the Earth gets cut in half, and the two sides start separating. Again, what nonesense.

[Batcathat]

The first result we see of it was that they had cut Jupiter in half. We clearly see in the comic the GAS GIANT cut in two clean halves.

That does raise a question for the scientifically minded people around here, what would happen if Jupiter got sliced in half like that? Would it stay more or less the same thanks to gravity holding it together or would it mess things up?

[halfeye]

Would it stay more or less the same thanks to gravity holding it together or would it mess things up?

It would stay the same due to gravity holding it together.

[Imbalance]

If it's transdimensional, its physical separation may only be apparent to the viewer on this plane. Elsewhere, an observer sees an odd slice of planet floating where none had been. And, if the transdimensional effect is persistent, the portions still rotate together as if they are all still a single body, with the parts all passing through the series of portals and back again, like slowly stepping through a wormhole's event horizon, your back foot standing firm on homeworld while the rest of you is presently emerging millions of lightyears away.

[halfeye]

If it's transdimensional, its physical separation may only be apparent to the viewer on this plane. Elsewhere, an observer sees an odd slice of planet floating where none had been. And, if the transdimensional effect is persistent, the portions still rotate together as if they are all still a single body, with the parts all passing through the series of portals and back again, like slowly stepping through a wormhole's event horizon, your back foot standing firm on homeworld while the rest of you is presently emerging millions of lightyears away.

Yeah, magic does whatever magic wants.

[Jay R]

That does raise a question for the scientifically minded people around here, what would happen if Jupiter got sliced in half like that? Would it stay more or less the same thanks to gravity holding it together or would it mess things up?

Pour yourself a glass of water. Then put a knife in the glass, and cut the water in half. You will find that the two halves are just a glass of water.

Similarly, after Jupiter has been sliced, you will have two semi-balls of gas, right up against each other. That is not in any way different from a single ball of gas.

[crayzz]

To my understanding, Jupiter is believed to have a solid core, somewhat larger than 10x the mass of earth.

Although, realistically, cutting it in half likely wouldn't due much. With that much gravity it's just going to refuse together practically instantly.

[Batcathat]

Pour yourself a glass of water. Then put a knife in the glass, and cut the water in half. You will find that the two halves are just a glass of water.

Similarly, after Jupiter has been sliced, you will have two semi-balls of gas, right up against each other. That is not in any way different from a single ball of gas.

Yeah, I suspected something like that, but I've learned that what I think seems reasonable and what can be proven by science doesn't always overlap. Especially on a literally astronomical scale.

Follow-up question: what (if anything) would happen if the Earth or a similar planet was sliced in half?

[Eldan]

Terrestrial Planet would reform too, if cut in half. The question is how much energy would be released in the process, i.e. if we're talking "just" unprecedentend global Earthquakes or "entire planet melts, then cools down again".

[Squire Doodad]

Yeah, if the gap is big enough to be visible, any cut stretching the length of the entire planet will cause major earthquakes.

[halfeye]

Follow-up question: what (if anything) would happen if the Earth or a similar planet was sliced in half?

This is very silly, there is no way to actually do this. When an object is pulled apart by gravity, the two halves are pulled out of shape before they part, they aren't hemispheres at that point.

That said, there are billions of possibilities, of which I'll pick a selection.

If the cut was on a scale to pass in between all the gluons and quarks, and the energy stayed the same, the cut would be undone so fast, with so little effect, that for all we know it happens twice a second every second and no-one knows. It probably doesn't happen, but there's really no telling.

Spoiler: bad options

Show

If it was a cut that left a one millimetre gap, there would be tsunamis all the way up Everest, all the volcanoes would erupt, there would be eruptions along the line of the cut, and there would be one huge earthquake that would flatten everything. We might survive as a species, but most people and all the current nations would be gone.

If there was a gap of about 100 metres, we would all suffer the effects of a 100 metre fall. A fall onto water is like a fall onto concrete at that speed. There would be survivors due to statistically improbable events happening to one or two individuals, but most people, animals and plants would be dead. Some waterbourne bacteria might survive?

A gap and fall of a kilometre would kill almost everything, including most bacteria.

When we have a gap big enough that the two halves don't fall together, then it matters to the planet (but we're dead, so do we care?) whether the gap is created by destroying a slice of the planet, or teleporting the halves apart.

With the destroyed slice, by the time the bits don't come together, most of the planet has been disintegrated, and what is left are two moderately sized saucer shaped asteroids, which might even retain most of their shapes if they're light enough and cold enough.

When the gap is created by teleporting the halves apart and they don't fall together, then something fairly spectacular happens to the halves, more or less the same thing to each of them, which is:- The gases in the core and the mantle are release by the drop in pressure. Simultaneously, the core and the mantle bulge down and fall toward the centre of the core, with the crust following the mantle down. At this stage the whole thing is at least red hot. Then the half planet forms into a sphere. The atmosphere reforms, as do the seas, there might be some high mountains since gravity is halved, but there is no life.

[Cikomyr2]

This is very silly, there is no way to actually do this. When an object is pulled apart by gravity, the two halves are pulled out of shape before they part, they aren't hemispheres at that point.

That said, there are billions of possibilities, of which I'll pick a selection.

If the cut was on a scale to pass in between all the gluons and quarks, and the energy stayed the same, the cut would be undone so fast, with so little effect, that for all we know it happens twice a second every second and no-one knows. It probably doesn't happen, but there's really no telling.

Spoiler: bad options

Show

If it was a cut that left a one millimetre gap, there would be tsunamis all the way up Everest, all the volcanoes would erupt, there would be eruptions along the line of the cut, and there would be one huge earthquake that would flatten everything. We might survive as a species, but most people and all the current nations would be gone.

If there was a gap of about 100 metres, we would all suffer the effects of a 100 metre fall. A fall onto water is like a fall onto concrete at that speed. There would be survivors due to statistically improbable events happening to one or two individuals, but most people, animals and plants would be dead. Some waterbourne bacteria might survive?

A gap and fall of a kilometre would kill almost everything, including most bacteria.

When we have a gap big enough that the two halves don't fall together, then it matters to the planet (but we're dead, so do we care?) whether the gap is created by destroying a slice of the planet, or teleporting the halves apart.

With the destroyed slice, by the time the bits don't come together, most of the planet has been disintegrated, and what is left are two moderately sized saucer shaped asteroids, which might even retain most of their shapes if they're light enough and cold enough.

When the gap is created by teleporting the halves apart and they don't fall together, then something fairly spectacular happens to the halves, more or less the same thing to each of them, which is:- The gases in the core and the mantle are release by the drop in pressure. Simultaneously, the core and the mantle bulge down and fall toward the centre of the core, with the crust following the mantle down. At this stage the whole thing is at least red hot. Then the half planet forms into a sphere. The atmosphere reforms, as do the seas, there might be some high mountains since gravity is halved, but there is no life.

Well, in the comic the earth also was cleanly cut in half with the transdimensional superweapon, so i would have assumed gravity would have kept yhe two halves together. Its just that there might have been a bit of magma release to reseal everything.

[hamishspence]

Nope. 2 billion cm = 20 million m = 20,000 km. The moon is already around 380,000 km away - going to 400,000 km is not going to make an enormous visual or gravitational difference - only a slight one.

[Lord Torath]

Nope. 2 billion cm = 20 million m = 20,000 km. The moon is already around 380,000 km away - going to 400,000 km is not going to make an enormous visual or gravitational difference - only a slight one.

Heck, it already varies in distance between 360,000 km and 400,000 km just because it has an elliptical orbit. In 5 - 7 billion years it'll be invisible because Earth will be inside the sun, though.

[hamishspence]

Yup - while the Sun's mass loss might lead to the Earth and Moon migrating out a bit, the Sun's massive size increase may possibly counter that, with the Earth being dragged in thanks to tidal forces, even if drag from the atmosphere doesn't do it.