What would happen to an Earth-like planet if its core completely and instantly vanished? Would the planet begin to pull in on itself due to asymmetry and the empty space in the middle, or would it begin to fail due to another factor? Or would it remain (relatively) unscathed? If so, for how long?
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$\begingroup$ (Pure Speculation) - I think the Earth would get destabilized, collapse and it would end up crushed with the Moon into a new planet. If the Core gets teleported nearby, - the collapse would be immediately subject to the Core's gravitational pull? And just re-crush itself into a new earth again (possibly dragging the Moon out of orbit at the same time into an even bigger earth) $\endgroup$– SpacemonkeyApr 16, 2015 at 17:54
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$\begingroup$ @2012rcampion he is probably refering to the question before I edited it. It was about teleportation, but I decided to cut to the chase and set it to something more simipiler. $\endgroup$– The ManApr 16, 2015 at 17:55
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2$\begingroup$ Inner and outer core? $\endgroup$– 2012rcampionApr 16, 2015 at 17:57
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4$\begingroup$ @Spacemonkey The moon would actually go spinning off into space (or the Sun) due to the reduction in gravity from the Earth. $\endgroup$– 2012rcampionApr 16, 2015 at 17:57
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1$\begingroup$ The moon's orbit would definitely be disturbed. Whether it escapes depends on how much of the core exactly vanishes. Either way, every living thing on the earth is going to die. $\endgroup$– ResonatingApr 16, 2015 at 18:03
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2 Answers
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Collapse.
Gravity takes care of this. As soon as you remove the core from the Earth, you have a large void in the middle of it, and a lot of gravity acting straight towards the centre of that void. The void may also be a vacuum - depending on whether you replace the core with air or not - which will accelerate the collapse.
It is worth noting that this is only possible because the mantle is liquid. If it were solid, the spherical shape would hold it together and the Earth would retain its shape.
As Spacemonkey has said, the resulting loss of mass of the Earth would disturb the Moon's orbit. I'll go into some basic orbital mechanics to show why and how.
The Moon has a stable orbit around Earth because as its velocity carries it forward, the gravity of the Earth pulls it sideways, resulting in a perpetual circle:
If the mass of the Earth decreases suddenly, so does the sideways force on the Moon, so it moves more straight - away from Earth. As it does this, the force decreases further, so it moves even further away, and so on:
This is... bad. Not only has everyone already died because everything collapsed underneath them, but scientists predict bad things if we lose the moon.
In short: everyone dies.
answered Apr 16, 2015 at 18:40
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$\begingroup$ In the diagrams, which way is toward the Sun? $\endgroup$– HDE 226868 ♦Apr 16, 2015 at 18:42
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2$\begingroup$ Actually, being liquid isn't required for collapse. A sphere wouldn't be able to contain a hard vacuum no matter what state it was in. Replacing it with air is a strange assumption, but even then, the pressure is minor compared to the outside. A single point crumbling would cascade a collapse across the whole structure. Perhaps if the remaining inner shell was airtight and pressurized with gas, but that's an even more bizarre assumption. $\endgroup$– SamuelApr 16, 2015 at 19:07
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1$\begingroup$ @Samuel I pretty much agree. Assuming the material on the inner surface of the now-hollow earth wouldn't crumble is similar to assuming you can tunnel through the side of a mountain and the top of your tunnel won't crumble either. Miners always support their tunnel ceilings with posts & cross braces. $\endgroup$ Apr 16, 2015 at 19:28
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3$\begingroup$ @HDE226868, it's irrelevant which direction is towards the sun. Even if the moon leaves Earth's orbit, it won't go crashing into the sun - the combined Earth-Moon system is still going ~30 km/s, and it's all traveling around the sun. The Moon, meanwhile, is only going 1 km/s relative to Earth. So when the Moon leaves the Earth, it'll end up in some kind of more-elliptical-than-usual orbit (the exact orbit depending on exactly where the Moon is when Earth's core vanishes), but it'll still be going around the sun. $\endgroup$ Apr 16, 2015 at 20:28
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1$\begingroup$ Actually the moon is unlikely to be at escape velocity, it will settle down into a new highly eliptical orbit. $\endgroup$– Tim BApr 17, 2015 at 8:38
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The planet would implode.
You've instantly removed the core. So what's in its place? Hard vacuum. There is a relevant xkcd for a similar scenario.
Outside of the core-vacuum is a molten magma. The pressure exerted from the Earth on the other side of that magma is still present and the magma will be blown, violently, into the suddenly empty space. This rapid movement will ripple up to the surface of the Earth along the most fluid paths. This will take about five minutes. Basically, it would be like every volcano erupting, at once, in reverse. The entire surface of the Earth would likely experience double digit Richter scale values. The magma rushing into the vacuum would slam into magma coming the other direction at very high velocity and, five minutes later, the shockwave would make all the volcanoes and new fissures on Earth erupt at once, in the normal direction.
This would most certainly be an extinction level event. All life bigger than bacteria would die immediately, probably in the first ten minutes during the collapse. The rest of the life would die during the world wide eruptions and when the atmosphere escapes the Earth's corpse.
The moon would probably stick around for a little while.
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$\begingroup$ At the risk of providing a useless comment: I often wonder if / hope that XKCD will be part of this community. $\endgroup$– MikeyApr 16, 2015 at 18:55
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$\begingroup$ You wouldn't need to wait for the shock wave. First, after the magma core, all of Earth crust gets sucked down and simultaneously crunched laterally (Earth radius just got smaller, "too big skin on too small ball"), but the moment the drop stops, it would crash hard against the magma core and sink into the magma. Only few airborne bacteria would survive that moment, then would quickly die in convection of overheated air and steam. $\endgroup$– SF.Apr 16, 2015 at 20:03
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1$\begingroup$ There wouldn't be suction in the manner in which you describe. Suction is just higher pressure pushing something into lower a lower pressure area. The force of the mass of the unsupported mantle would be far greater than that of any atmospheric pressure pushing it into the now vacant core. @Samuel, udder destruction is feeding a cow sticks of dynamite, n'est pas? lol $\endgroup$– Jim2BApr 17, 2015 at 0:39
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1$\begingroup$ At time step 1 (instant after core implosion) the lowest slice of mantle has 0 pascals on the lower side and 360 GPa on the other. This (and its own gravitational acceleration) accelerates the inner slice so it is no longer in contact with the second slice up. At time step 2, the innermost slice has pressure 0 on top and bottom but slice 2 has 0 pascals on the lower side and 360 GPa on its upper slice. What I'm saying is that this pressure only acts as an initial acceleration after which the fall is purely ballistic. $\endgroup$– Jim2BApr 17, 2015 at 3:16
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1$\begingroup$ This doesn't change the results though. Everything @Samuel mentioned still happens (fall, compression faulting at every level of the Earth, collision & rebound at the center causing a shock wave to propagate outwards, followed by it blowing off portions of the Earth). Plus the fall releases tons of potential energy which heats things up and generally kills everything in a most spectacular fashion. $\endgroup$– Jim2BApr 17, 2015 at 3:24