What would happen to a planet without its core?
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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1 answer
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.
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