3
$\begingroup$

What would happen to a planet if its core suddenly disappeared?

I'm talking instantly and without warning, gone. I'm not concerned with how scientifically accurate this would be, because I'm absolutely sure it's impossible. I'm instead concerned with how the mantle, crust, and other parts/layers of the planet would react. Please provide some sort of scientific explanation with your claim, thanks.

$\endgroup$
  • 8
    $\begingroup$ Please clarify...what kind of planet is it? A gas-giant? A rock planet? A dwarf planet? The answer would be very different for each of these kinds of planets. $\endgroup$ – NL628 Dec 28 '17 at 3:46
  • 1
    $\begingroup$ +NL628 Terrestrial Planet similar to Earth $\endgroup$ – Rangoon Dec 28 '17 at 4:54
  • 1
    $\begingroup$ What is it replaced with? A vacuum? Magma? Air? $\endgroup$ – bendl Dec 28 '17 at 14:59
  • 1
    $\begingroup$ +bendl It would be a vacuum $\endgroup$ – Rangoon Dec 28 '17 at 15:41
  • 1
    $\begingroup$ @SaltedAss this if you want to direct yout answer you can put an @ in front of the username instead of the + you use. The system will recognize it and give the user a notification. This only works for users that have commented at least once though. $\endgroup$ – dot_Sp0T Dec 28 '17 at 20:28
8
$\begingroup$

Nature abhors a vacuum

The most likely result would be the instantaneous collapse of the planet, due both to gravitational forces and the force implosed by the vacuum left behind.

But, moments before that happened, everyone on the planet would vomit from the sudden drop in gravitational force. Heart attacks would occur, especially amongst the elderly.

The two people who are surviving these moments (probably because they're roller coaster buffs) would notice world-class aurora borealis as the magnetosphere experiences massive changes in its flux density.

But they wouldn't even have time to smile before the implosion happened.

What happens after is the generation of tremendous heat as a bazillion tons of mass begin to grind together, seeking equilibrium. There's no life left on the mass, but it might not completely devolve into debris (depending on its initial mass and the amount of mass left behind). However, any moons the planet once had have now spun off into space to become everything from asteroids to planetoids of their own to meteors impacting the sun.

The entire solar system would then shudder. It would take years... centuries... eons... for everything to balance itself out, but you can't significantly change planetary mass without affecting every other planet in the system. Most would simply fall into slightly modified orbits. But that really depends on the orbits and mass beforhand, which we know absolutely nothing about.

$\endgroup$
  • 6
    $\begingroup$ Force of gravity on a person is directly proportional to the mass of the planet. The core is about 1/3 of the mass, so gravity will drop to 2/3 of normal. I don't think I would puke. I don't even think many people would die. I mean, before the Earth collapsed and we all die. $\endgroup$ – kingledion Dec 28 '17 at 5:06
  • 4
    $\begingroup$ Also the effects of even Jupiter's gravity on other planets is not very big. Earth disapearing won't be a big deal to any other planets. Except the moon, of course. $\endgroup$ – kingledion Dec 28 '17 at 5:08
  • 2
    $\begingroup$ How would the vacuum of space exert any force on the vacuum left where the core was? $\endgroup$ – L.Dutch Dec 28 '17 at 6:20
  • 3
    $\begingroup$ @bendl The ground would not "fall out from under them". They would fall with the ground. $\endgroup$ – Azuaron Dec 28 '17 at 16:20
  • 2
    $\begingroup$ Vacuum does not exert a force. Pressure exerts force which a vacuum doesn't resist. In this case the implosion happens because of gravity alone, and only if the cohesive forces don't hold it together for a few days first. $\endgroup$ – Muuski Dec 28 '17 at 17:37
5
$\begingroup$

I"m going to go the opposite direction of @JBH, and say that not much is going to happen right away.

Sure, gravity will lessen instantly, but that's about it for instantaneous effects. Granted, there's a lot of things that rely on gravity to "do it's thing", but I doubt the planet would crumble in on itself.

https://en.wikipedia.org/wiki/Structure_of_the_Earth

That Wiki page shows that the inner and even outer core are relatively small parts of the inner Earth. The mantle is almost 1800 miles thick and solid rock. The page explains that at the pressure it's at, it can move, but only slowly. Even if layers of the inner mantle implode to release pressure, there's only a specific amount of room for that to happen, so the pressure should reach equilibrium over time. It may take millennia before any of that happens, or it could happen in minutes, potentially without the (average) surface dwellers even knowing about it.

There are plenty of large caves that show the Earth is self supporting.

https://www.huffingtonpost.com/2015/12/26/son-doong_n_3873341.html

Think about an archway. If it's constructed correctly, the whole arch sees pretty much the same force, as the keystone spreads the forces it sees down to the supported structure below. A sphere, even a hollow one, is very hard to compress in all directions at once. Even something as fluid as sand will stop moving and be stuck in a funnel, if there's too much compaction and not enough freedom of movement.

What will eventually and gradually happen is that the planet will move to a different orbit. The gravitational constant for the planet will have changed, due to the mass changing, so that changes the pull of the plant towards the star it's orbiting.

https://en.wikipedia.org/wiki/Orbital_mechanics#Laws_of_astrodynamics

I don't have the time or the math chops anymore, or I'd try to figure out how much difference that is. It would definitely change the temperature of the planet, but without doing the math, I don't know if it would stay in the circumstellar habitable zone for life to remain viable easily. I don't even know how long it would take if it didn't stay there, but I'd have to guess thousands or tens of thousands of years.

https://en.wikipedia.org/wiki/Circumstellar_habitable_zone

The planet would also slowly cool due to the molten core (of Earth) providing a considerable amount of heat to it's surface.

https://en.wikipedia.org/wiki/Internal_heating

You also have to take into account whether the atmosphere would remain, since it's held in by gravity.

https://en.wikipedia.org/wiki/Atmosphere#Atmospheric_escape

Any plane would probably crash. The down force counteracted by it's lift would dramatically change. They would have a tendency to have too much lift, so if the pilot wasn't skilled enough, the plane not aerobatic enough, or 1000 other problems could cause the plane to shoot up, stall, flip, or otherwise become unable to be controlled. Anything flying on autopilot would have to go to manual mode, with the autopilots having to be reprogrammed before being usable again. But that's a surface dweller problem, not a planetary concern.

$\endgroup$
  • 1
    $\begingroup$ I'm no physics expert but I think this answer makes more sense. A hollow planet is essentially a giant egg shell with gravity compressing it from all directions equally. Therefore, I think it wouldn't collapse immediately. However, pieces of the mantle would eventually break off (on the inner side) and fall away. Eventually gravity would overcome the weakening structural integrity, much the same way that a tunnel through wet sand collapses. That could take years or even longer. $\endgroup$ – Charles Burge Dec 28 '17 at 21:05
  • 1
    $\begingroup$ I think the pressure is too great at the mantle to allow for any structural integrity of the solid to stabilize the structure even in the short term. You might think the solid rock would be able to withstand pressure given the geometry but when you are that deep, the pressure especially with the vacuum will make even small instabilities collapse the whole system. And tidal forces from the moon will quickly break the equilibrium even if you had a perfectly balanced cavity. Although the moon will likely be flung out into space in this case rather quickly. $\endgroup$ – A. C. A. C. Dec 28 '17 at 22:06
  • 1
    $\begingroup$ This answer doesn't seem to get a handle on the massive forces involved. 1.3 billion newtons per square metre, it is enough to bend and crush any rock that isn't supported by an ocean of iron under equal pressure. Instead of a wet sand bridge, imagine one made of dry sand. However the Earth won't be flung out of orbit, the "Gravitational constant" is G(M+m), where M is the mass of the sun and m is the mass of the Earth, as the Sun isn't changing mass, the Gravitational constant is almost the same. $\endgroup$ – James K Dec 29 '17 at 21:54
  • 1
    $\begingroup$ @JamesK, I never said my sand was wet and I've seen dry sand get compacted in a funnel to where it won't move without tapping the side. Regardless, since you seem to have a handle on the conditions going on inside the Earth and the math to go with it, I invite you to post your own answer here. Vance49 seems to have a good explanation, too, but maybe you can expand on what happens with the inner planet. $\endgroup$ – computercarguy Dec 29 '17 at 22:18
  • $\begingroup$ @JamesK the answerer didn't say "flung out of space". Rather, it says "thousands or tens of thousands of years". That is, it will shift its orbit because of interactions with other bodies. Such as the solar wind it now absorbs instead of deflecting due to the missing magnetosphere, or the atmosphere it doesn't have? The lack of a moon would also have an effect. $\endgroup$ – John Dvorak Dec 30 '17 at 0:20
3
$\begingroup$

If the Earth's core was removed (gradually or instantaneously), the primary effect would be loss of the global magnetic field.

The mean distance of the Earth from the Sun would change by less than 1 part in a million.

Although the first two are factual, I think the surface would not sink significantly, at least in the short term.

The Earth's global magnetic field is due to the rotation of the Earth and the (slightly out of phase) rotation of the liquid core. If the core was removed, or just vitrified, the global magnetic field would collapse. This results in two issues that would eventually destroy human civilization (at least as we know it now).

The first issue is, without a magnetic field, the Earth would have no defense against solar storms (and less protection from cosmic rays). We haven't experienced a major solar storm for over 150 years, although one just missed us in July 2012. The 2012 event was about the same magnitude as the solar storm of 1859. One study estimated that, if a storm of that strength hit Earth now, it would take between 4 and 10 years for power and other services to be fully restored. And that was if we had a magnetic field!

The second issue is the erosion of the atmosphere by the solar wind. We have an example of that with Mars. Since Mars is smaller than Earth, it has a smaller heat capacity and a greater surface to volume ratio, so its core cooled much sooner than Earth's will. According to data collected from the Mars Global Surveyor by the late Mario Acuna, Mars' core began to vitrify about 1 billion years after its formation. That explains why, long ago, Mars had a sufficiently dense atmosphere to support liquid water on the surface, and now has almost none (about 0.007% of Earth's atmosphere).

Looking at Wikipedia, or any physics text, you will see that in the equation for the mean orbital distance in a two-body problem, the sum of the masses is in the denominator. The mass of the Sun is about 333,000 times greater than that of Earth. Since the core is a small fraction of Earth's mass, the change in the sum of the two, and thus the change in Earth's mean distance from the Sun, would be less than 1 part in a million.

The Earth's construction is complex and the exact mechanical properties of many of its components are not well known, so I can only say I think nothing catastrophic would happen in the short term.

It's the loss of the magnetic field that's the big deal.

/// Note: the description of the effects of loss of the magnetic field described above is a simplification of a complex event. Although it's true that Earth's magnetic field protects us from being directly bombarded by Coronal Mass Ejections (CMEs), it's the presence of a magnetic field that causes the greatest threat to our digital world. When bombarded by CMEs, the huge movement of the magnetic fields as they collapse induces equally huge currents in anything that conducts electricity. The result is almost all electric devices are fried--permanently. ///

In the links below, I've favored Wikipedia, as it is free for everyone, which is often not the case for scientific papers.

The Solar Storm of 1859: https://en.wikipedia.org/wiki/Solar_storm_of_1859

The Solar Storm of 2012: https://en.wikipedia.org/wiki/Solar_storm_of_2012

Calculating the Mean Orbital Distance: https://en.wikipedia.org/wiki/Orbital_mechanics#Laws_of_astrodynamics

Mars Global Surveyor Magnetic Field Mission: https://mgs-mager.gsfc.nasa.gov/

How Earth's Magnetic Field is Generated: https://en.wikipedia.org/wiki/Earth%27s_magnetic_field#Earth%27s_core_and_the_geodynamo

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.