An alien species has created a weapon. The alien stands on a planet, points the weapon at the ground, and pushes a button. A large amount of matter condenses itself into a mass, creating a huge hole in the planet's mantle. The mass is like a time bomb that gives the alien enough time to escape through a portal. The mass explodes, cutting a huge chunk out of the earth.

I'm assuming the liquid metal insides of the planet would start to come out. Would the liquid harden since it's exposed?

The explosion would likely kill all life on the planet. Would the planet collapse on itself to reform a sphere? What would happen to the planet's orbit?

  • $\begingroup$ Hello Lindy Ray, and welcome to Worldbuilding. While this seems like an interesting question, it needs a little more specification. What happens to the "chunk" of the earth that is cut out, exactly how much of it is removed, and how deep does this go? In any case, it seems exceedingly unlikely that anything on the surface will survive. Please visit our help center and take the tour to learn more about the site. Have a nice day! $\endgroup$ – Gryphon Jun 14 '18 at 17:55
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    $\begingroup$ A much, much smaller explosion would easily and thoroughly eradicate all life. An explosion of that magnitude would create a new temporary asteroid belt. $\endgroup$ – user535733 Jun 14 '18 at 17:59
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    $\begingroup$ Seems a rather pointless weapon. Removing a quarter of the planet explosively would simply destroy the planet and render it uninhabitable for a geologically significant time (e.g. or the order of a billion years perhaps). It would be something on a similar order of magnitude to the impact that is thought to have created the Earth-Moon system. Aliens capable of making portals that they can escape through would presumably have no purpose in doing this as it implies a tech level making planets rather irrelevant. $\endgroup$ – StephenG Jun 14 '18 at 18:14

This actually sounds strikingly similar (in effect, if not cause) to the giant impact hypothesis of the Moon's formation. The gist of this hypothesis is that the young Earth was struck by a Mars-sized body named Theia. Most of Theia's mass was subsumed by the Earth; some of it was blown into orbit and coalesced into the Moon.

The immediate effect was that both bodies were heated to such a degree that their entire crust was turned to magma. As a result, both the Earth and Moon eventually became mostly round, differentiated bodies despite any transient deformation. (This is very much a live topic of research, though, and while the basic theory is pretty sound, the models of what happened after the impact need work. For instance, there's a model that suggests the Earth-Moon system spent some time as a torus before collapsing further into separate bodies, or that the impact actually formed two moons which eventually merged.)

Differentiation is the key. This is the process by which planets like Earth end up with an iron core and a lighter (mostly silicate) crust, and is driven by the relative densities of materials. Heavier materials settle to the bottom, while lighter materials are raised upwards by buoyancy. After the giant impact, Earth's and Theia's cores merged into a single iron core, and the same thing seems likely to happen here. Even if part of the core is exposed in the blast, it will take a long time for the planet to cool down enough to harden into a new configuration.

So to sum up: the planet's crust will be reduced to magma for a prolonged period. While it cools, the planet will reshape itself into a differentiated sphere with a core, mantle, and crust similar to what it has now. Depending on the force of the explosion, some of the material may end up in orbit, where it will also shape itself into a sphere (assuming there's enough of it), forming something akin to the Moon. (If you do this to Earth, the Moon is probably fine; it will gradually "sweep up" all the leftover debris, becoming somewhat larger.)

(Edit: thanks to not store bought dirt for reminding me of the difference between centrifugal sorting and buoyancy sorting.)

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    $\begingroup$ In a centrifuge the denser stuff ends up on the outside. Centrifuging is interesting in production of the bands on the gas giants, but I don't think it has much impact on rocks. I think buoyancy is the normal explanation of how the layers were sorted. $\endgroup$ – user25818 Jun 14 '18 at 19:03
  • $\begingroup$ That's what I get for sleeping through freshman earth sciences. I'll correct it. $\endgroup$ – Cadence Jun 14 '18 at 19:44
  • $\begingroup$ It's also somewhat similar to the climax of the sci-fi film Crack in the World. A massive fissure races across the earth, effectively slicing a divot out of the crust, which pops out like a cork, flying into space and forming a second moon. The film goes nowhere near addressing the results of a massive swath of the mantle becoming exposed. Indeed, the main characters are standing at the edge where the section was expelled, and they're perfectly fine. So, movies. $\endgroup$ – VBartilucci Jun 15 '18 at 13:43

The pressures deep in the mantle are immense. The moment you condense the mass, you're left with a gaping hole. That hole is unstable, as you've guessed, so the surrounding material will move to fill in the empty space. As Cadence mentioned, this will not be dissimilar to the creation of the moon, but there are some differences - firstly, it's going to be way less intense.

Way less intense on this scale still means everything dies very quickly, but not quite as dramatically. As the hole begins to fill itself in, the ground above will drop. Absolutely massive earthquakes will occur worldwide, and everyone nearby will die almost immediately.

My gut instinct is that nearly everyone on the other side of the world will also be killed by movements in the crust very quickly, but if anyone happens to survive long enough, they'll get to experience the world's biggest thunderstorm (maybe) before asphyxiating. When you remove that huge chunk of crust, the atmosphere will be sucked into the new vacuum and therefore out of the rest of the world. Wind speeds will be enormous. When all sides meet in the center, you'll have the world's biggest thunderclap.

Within a few minutes everyone will be dead, and (this is more gut instinct) in less than 24 hours the planet will have rearranged itself back into a glowing sphere of magma.

Depending on how long you wait to release all the mass you're storing this process will be interrupted by the complete disintegration of the Earth. You won't want to be anywhere near the Earth when that happens.

  • $\begingroup$ Think of the earth as s giant ball of molten iron with the solid surface being proportionately scaled to the relative thickness of an orange peel. Your instincts are essentially correct, but i think too mild in scope. The collapse into a sphere would begin immediately and be complete in a few hours, except for surface "ripples" and temporary ejecta (more NEO's ) that will be recaptured and become part of the new surface over time. $\endgroup$ – pojo-guy Jun 14 '18 at 19:56
  • $\begingroup$ @pojo-guy I agree, but without any data, I went for a conservative upper bound. It will certainly be done before 24 hours. $\endgroup$ – bendl Jun 14 '18 at 20:58

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