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In the movie Oblivion, the Moon has been destroyed by invading aliens. Several shots of the moon show what is left: enter image description here

If the moon was somehow shattered like this, what would the effect be on Earth?

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    $\begingroup$ Possible duplicate of worldbuilding.stackexchange.com/questions/14755/…, unless in this scenario the Moon remains partially intact. The effects are going to be pretty much the same, though. $\endgroup$ – HDE 226868 Nov 6 '15 at 23:40
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    $\begingroup$ @HDE226868 I think they'd be quite different. All the mass is still there and its center has hardly changed. It's be more like nothing changed than no moon at all. $\endgroup$ – Samuel Nov 6 '15 at 23:42
  • $\begingroup$ @Samuel Tommy states that the Moon is destroyed; I took that to mean that it had essentially been blown up such that there was nothing left where it used to be. $\endgroup$ – HDE 226868 Nov 6 '15 at 23:44
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    $\begingroup$ Related: Conditions needed for a Fractured Moon. I knew I'd seen that picture around here somewhere. $\endgroup$ – Frostfyre Nov 7 '15 at 0:48
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    $\begingroup$ Neal Stephenson's novel 'Seveneves' deals with this exact scenario. Its quite a read though. $\endgroup$ – WarPorcus Nov 7 '15 at 1:10
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It Depends

Case 1 - The earth gains a ring. This case arises when the debris will stay in orbit but not be pulled in by the gravity of the remaining moon. Every night is a little brighter. As the ring gets more evenly distributed, tides would become less severe and eventually die out. Check out this huffington post article about "if the Earth had rings." Some rings may also help with navigation, making finding north trivial.

Case 2 - The moon's (or its debris') orbit decays. In which case, the moon (or its debris) will slam (or return?) into the Earth. Any significant portion of the moon that makes it to earth makes the astroid which killed the dinosaurs look like a bug hitting a car's windshield. The moon or its debris kills almost all surface life. Also, global cooling would occur from the dirt kicked up by the impact(s), not that most creatures would be around to complain about it.

Case 3 - The moon is only temporarily disassembled. If the debris from the shattered moon is still mostly under the gravitational effect of the moon, it'll fall back down and re-form the moon! This may take a while, since the gravity of the moon is weak. The new moon would, most likely, not look like the current one. In the meantime, the tides and most life continues on earth almost like it never happened.

Case 4 - The moon has gained some energy so it can get our of its orbit. This event looks like it was really, really big. Maybe it gave the moon (or big enough chunks of it) enough energy to get out of orbit with the earth. In which case, the moon will appear (from Earth) to shrink into the sky, until it is gone entirely. Tides would subside. Animals and plants would need to adapt to the new, moon-less world. Over a larger timescale you'd also see a significant increase in the variability of the tilt of earth's rotation, making seasons less predictable and generally making life much tougher - one discussion is this article.

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  • $\begingroup$ Very interesting answer. What would cause the first two scenarios though? For example, what determines if the orbit decays instead of a ring forming? $\endgroup$ – Thomas Myron Nov 7 '15 at 0:04
  • $\begingroup$ @TommyMyron To really understand the nitty-gritty of how these situations can come about, you need to know orbital mechanics, which is too large a subject to explain here. As a terribly short summary: an orbit is determined by how quickly an object goes around the thing its orbiting and the (radial) distance from that thing. Case 1- the debris maintains it's speed and distance from earth, but not from each other. Case 2 - the speed (or distance) of the debris falls below the orbit required, and comes back to hit earth. Astronomers could likely tell your more. $\endgroup$ – PipperChip Nov 7 '15 at 0:12
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    $\begingroup$ Much of that will be determined by "how" the moon was shattered. The energy needed to shatter a moon or planet is colossal, and if it was directed in the right manner, it would also provide a velocity vector to the moon or debris, changing the orbit(s). $\endgroup$ – Thucydides Nov 7 '15 at 0:41
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    $\begingroup$ Excellent answer. I'd like to add that if the moon were knocked out of orbit and it didn't achieve escape velocity, it could also be that it might enter a more elliptical orbit which could change the tides and other things related to the moon as it is now. Also, it is unlikely that it would also be knocked out of the sun's orbit so in a story, accounting for where the moon went, might need to be addressed. $\endgroup$ – ozone Nov 7 '15 at 2:45
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    $\begingroup$ Besides the actual physical orbital mechanics part of this, you also have the 'softer' sciences to consider. Many animals have different behaviors for various parts of the moon cycle. For example many species of Sea turtles will wait for the specific tide at a certain part of year to lay eggs on shore. On the human side, many religions still set their calendar by the moon. Ramadan for example, is set by sighting a certain phase of the moon at a certain time of year. No moon, or a moon that's shattered isn't going to have the same orbit or phases will be hard to see. Talk about social upheaval. $\endgroup$ – Zessa Nov 7 '15 at 7:12
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We'd be screwed.

The Earth relies on the moon to stabilise its orbit. A stable orbit is necessary for stable seasons, and its likely that complex multi-celled life could never have evolved without these. You'd be looking at apocalyptically random weather, and depending on the extent to which the moon was damaged, the potential destruction of all life on earth larger than bacteria.

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    $\begingroup$ The Earth relies on the moon to stabilise its orbit. What do you mean? Venus gets along just fine without any moons (as does Mercury!). $\endgroup$ – HDE 226868 Nov 7 '15 at 22:08
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    $\begingroup$ Over geological ages the Earth "wobbles" about its axis, causing the precession of the zodiac. Planets without a large moon to stabilize them will have a more extreme wobble, which might seem very small on the outside, will have huge impacts on climate (the shifting direction of the poles is though to cause ice ages on Earth, imagine the effect if the shift was faster than several thousand years or more extreme by a degree or more? $\endgroup$ – Thucydides Nov 8 '15 at 4:17
  • $\begingroup$ Thank you Thucydides. I couldn't remember the exact mechanism, nor find the book where i read it at the time of answering $\endgroup$ – Sven Carpenter Nov 9 '15 at 20:26

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