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I was thinking about this world with different ancient factions on war. The war caused both of them and most life on the planet to die, I was thinking about one of the moons getting shattered as a result of such war.

The humans that survived made their own society and remember little to no detail on how the world was before the war, it has been many years and nobody kept records of how life was back then.

I want to use the moons shattering because it is made of this mysterious mineral than can be used as fuel, it is rare but extremely efficient, and also because I want to show off how destructive that war was. The mineral can produce a significant amount of fuel without the need to posses a big amount of it. I want to know how viable a catastrophe such as a moon shattering would be for the plot, keeping in mind that the planet can continue to support life.

Maybe not keep the whole moon crashing on the planet, but have some of it orbit around the planet, and after many years some pieces fell on one side of the planet, the remaining pieces are somehow stable on the planet's orbit... But I don't know if any of that would be possible in the first place so it makes some sense!

What I would like to know is how to make it so the moon that shattered does not kill off the entire life on the planet?

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    $\begingroup$ Welcome to the site hOlim, please take the tour and read up in our help centre about how we work: How to Ask . Someone might answer your question, but at the moment it's not clear what you're asking, please read the help center to get a feel for what we are able to do. $\endgroup$ – Agrajag Mar 5 at 22:29
  • $\begingroup$ Oh, and you can edit your question, did I mention that? $\endgroup$ – Agrajag Mar 5 at 22:39
  • $\begingroup$ If i am understandig your question correctly, you are asking how a planetary body like a moon could be destroyed without devastating the planet it orbits? $\endgroup$ – DarthDonut Mar 6 at 7:44
  • $\begingroup$ @DarthDonut yes, there could be two or more around the planet, and I would like to know how a moon like body could be shattered and not destroy the planet and its life. $\endgroup$ – hOlim Mar 6 at 15:04
  • $\begingroup$ ... and the other moon would need to stay whole? Are there any more constraints (if there was, say the constraint that the moon be much larger in the sky than ours is, that would say something about it's orbit; or if the constraint was that the moons are always visible at the same time, that would say something about their respective orbits, etc); A 'moon' is essentially any natural satellite of a planet, so you need to constrain how big or small it may be - otherwise a football-sized moon could be destroyed by a fast grain, and nobody on the planet would even notice until some fragements fell $\endgroup$ – bukwyrm Mar 13 at 8:02
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You have an entire moon made up of mysterious hyper-efficient fuel material, unless its a plutonium lodestone for a high tech civilization this doesn't sound like a hard science setting where you need to something to be actually possible rather than just explain it away as part of the fictional setting.

That said, I also think you're only considering Earth's moon, which at approx. 1:81 Earth mass is still among the bigger satellite bodies in the solar system. If a piece of our moon shattered and fell to Earth, it could cause a planetary extinction event. But if you think of much smaller satellites (relative to the planet itself) like the Jovian moons, then its quite possible for the planet's biosphere to survive, esp. nearer to the antipodal regions (other side of the globe).

I'm just saying, since its a fantasy setting why ask about whether a moon crash is 'possible in the first place'. If this story had to conform to RL physics, then your potential high-energy material would need to be something radioactive for really high energy density (which would have its own problems to explain why there's a big chunk of it orbiting the planet). If it doesn't care about RL physics, then pretty much anything can be viable.

My reference to plutonium was simply because its a known high energy material, albeit not naturally occurring on Earth. OP could go for a setting where say, a peace treaty attempt on the planet ended up with plutonium stocks exiled into space to form an artificial moon. Unfortunately this didn't actually end the war, and the two sides eventually fought and even shattered this big lump or resources.

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  • $\begingroup$ Hey, Alok, It's not clear what the OP was asking, and it's not clear what you're answering. Pseudo-scientific jargon such as plutonium lodestone realy doesn't help, and is off topic, unless many up-above tell us otherwise. $\endgroup$ – Agrajag Mar 5 at 23:56
  • $\begingroup$ @Agrajag Thanks for commenting on why the downvote - added explanation on why I referenced Pu at all, didn't think it would be considered off-topic. $\endgroup$ – Alok Mar 6 at 19:04
  • $\begingroup$ Downvote withdrawn. A plutonium moon (or at least partial Pu satelite), a bit of a stretch. Good save though. $\endgroup$ – Agrajag Mar 6 at 19:18
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It did kill everything off

If the war was big enough and advanced enough to destroy a moon why not just say that is what ended the war because all life on earth was just gone.

Now because they were in space or are a space faring factions (assumption based on how else could they destroy a moon) it could be said that the penalty for losing the war was to have their technology stripped and forcefully relocated to earth shortly after it was reseeded with basic life.

If the reseeding of life on earth is to much of hand waiving then most of life was gone and the remaining humans went underground / cryo and exited when life had regained a foot hold. History caused another dark age and that is why no one knows of it.

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Let's have a look on what happens when a planetary body is destroyed.
The energy required to shatter something that is hold together by gravity must be bigger than the potential gravitational energy. For the sake of this question I will asume that these moons are made up of homogenous material, and then the equation for the gravitational energy would be:

E = 3GM^2 / 5R

Here, G describes the universal gravitational constant, M the mass of the sphere and R the radius.
So, using our Moon as a reference, the minimum energy needed for shattering your moon would be 6.217×10^28 joules. For reference, that would be the energy of 2.97 * 10^11 or nearly 300 Billion Tzar Bombas!
What I want to say is, every event with less energy will have the shattered moon forming again, with maybe one or two chunks flying of, but everything more, and all debris will fly around! If you want your planet to survive, I would recommend using alot less energy than what I have calculated above.

Even with handwaving, if such massive amounts of energy are being thrown around, alot of it will be converted into radiation that will kill everything on the surface on your planet.

Result: You cannot shatter a moon without killing everything on the planet it orbits

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