Three related questions in the same scenario that build off one another.

Question 1: Could a terrestrial planet be broken into multiple pieces (2 or 3) and continue its orbit without colliding with one another, etc. if it was done by advanced being(s) who knew how to return it to a stable orbit? Would any atmosphere/magnetic field be effectively wiped out?

Question 2: Could complex life (plants & animals) living on that planet's surface survive the actual incident described in Q1, assuming it was done with precision/caution? What if they went underground or underwater or into shelters?

Question 3: Could the newly formed planets then continue to support life? What if they were made more dense/atmospheric through artificial means? Don't agree with theories of binary/trinary planets? Perhaps their rotation and revolution around the sun would also be maintained artificially.

I'm open to any brainstorming that would allow for some of this to be feasible. The division of the planet, the survival of a small percentage of life on that planet, and the possibility of repopulation of the subsequent smaller planets.

  • $\begingroup$ Could you clarify. Do you mean the mass is split into multiple smaller spheres or is someone halfing the Earth? This is important to determine if you have a magnetosphere or even uniform gravity remaining, which without you other two questions are moot. $\endgroup$
    – knowads
    Jun 24, 2016 at 20:46
  • $\begingroup$ "Halfing" or even "thirding" the earth-like planet. Segments that are maybe only partially spherical at first. If there is a need for them to be molded into spherical bodies I think the advanced beings could handle that. $\endgroup$
    – mordecai
    Jun 24, 2016 at 20:49
  • $\begingroup$ If you have a civilization capable of planet shaping, it's most likely easier to just use the fragments as material to construct artificial life-sustaining platforms (like a Stanford Torus) $\endgroup$
    – knowads
    Jun 24, 2016 at 21:09
  • $\begingroup$ This being my first question, i appreciate your patience. I'll do what I can to add a better overarching premise to my OP. $\endgroup$
    – mordecai
    Jun 24, 2016 at 21:32
  • $\begingroup$ These are good questions but we would prefer to have only 1 at a time if it's possible. $\endgroup$
    – Vincent
    Jun 25, 2016 at 15:36

3 Answers 3


Well, a lot of this depends on just how advanced these beings are, and how much they can mess around with physics. The necessary answers seem to be "Utterly godlike" and "Physics? Why would we bother with that?"

The first thing to understand us that the Earth isn't a rigid, solid body, on the scale of the whole planet. It's a stiff fluid, some parts being runnier than others. The continents are made of less dense rock that floats on top of the denser rock. Think of it as a ball of very hot jello, with a thin and weak skin.

So if you just put a cut through the planet, nothing much happens, on the scale of the planet. It's held together by gravity anyway. There will be earthquakes and volcanic eruptions on a vast scale, but the planet won't come apart. It's possible there'll be some surviving life, but I wouldn't bet on it.

If you can put two planes of force through the planet and move them apart, then things get very exciting. The halves of the planet want to get closer together, but your planes of force prevent this, so they start to flatten out against the plane of force. The earthquakes and volcanic eruptions this causes should finish off all life, convert the oceans to steam, and so on.

If you carry on regardless then as the two halves get further apart they will start to reshape into spheres under their own gravity, and at this point "earthquakes and volcanoes" becomes utterly inadequate to describe what happens, and you end up with two balls of molten rock, with atmospheres about as hot as that of Venus. All this has been done by Earth's own gravity, plus the energy that was used to move the planes of force apart against that gravity. A lot of the heat in the interior of the planet has had a chance to move around, and has had fun.

If you want to make this survivable, it gets a lot harder, and you need aliens sufficiently advanced to utterly ignore the laws of physics. At that point, they peel Earth's crust off, including the oceans, not spilling anything, and only using very low accelerations so that mountain ranges don't collapse. You move the peelings out of the way, supplying them with artificial gravity so the atmosphere doesn't take off, and putting walls round them so that the oceans don't spill off into space.

Then you chop up the mass of the planet into however many chunks you want, separate them, let them become spherical, wait a few thousand years for them to cool down a bit (stopping time for the peelings) then re-surface them with selected pieces of the peelings, adjusting the curvature to fit. You will also need to fit these new planets with some means of artificially maintaining their orbits, or to redesign the solar system, but either of those problems is trivial compared to the peeling and resurfacing problem.

It would probably be much easier to just scan the entire planet and duplicate the geography, life and ecology by construction from scratch in another solar system that had the right size of planets naturally.

Off-hand, I can't think of an SF civilisation that could do this readily. The Culture could probably manage it if they did some development work. The Transcendent Powers of A Fire Upon the Deep wouldn't bother - what would be the point of it for them? Indeed, this is the basic problem: anyone who could do it is so far beyond human-scale interests that it's hard to write a story about them. Bob Shaw's The Ragged Astronauts has something a bit similar, set in a universe where the laws of physics are utterly different. Charlie Stross' Missile Gap has a peeled Earth, done by creatures whose motives are explicitly incomprehensible to humanity.

  • $\begingroup$ Okay, impact on my worldbuilding aside, i just love your answer. I had a lot of fun reading it. :P I think if i want my world to be scientifically reasonable, I'll need to rethink my premise. But I just really like the imagery your answer has conjured up. $\endgroup$
    – mordecai
    Jun 24, 2016 at 21:35
  • $\begingroup$ Disasters are fun to write about. The bigger the better. $\endgroup$ Jun 24, 2016 at 21:38

Since you are thinking about a planet massive enough for it bearing life, it is safe to say that it has a molten mantle and is aproximatelly spheric.

Now, how can you chop a planet in two halves. It happens that there is no such process that is not extremely violent. Too violent for anything to survive.

  • If you just got a megalaser to cut it in two halves, gravity will quickly make the two halves join together.

  • If you just teleport away half of the planet to somewhere else, each half would then reduce itself to a spherical form. And this will be a very violent event. The core and the mantle will quickly flow and collapse out due to gravity and pressure to reform the absent hemisphere, spreading out shockwaves that will destroy everything up to the surface. After parts of the core and the mantle rushing through the lost half meet together, they will splash. A big splash in planetary scales. That would be the mother of all earthquakes. The heat generated will probably vaporize a good portion of the core and the mantle, so there is no chance for the surface and the atmosphere to ever thinking about any chance of surviving.

  • If you try to break a planet in pieces by throwing some large projectile, well, depends on the projectile. If you choose a small asteroid, it will wipe out dinosaurs, but this would not make a new planet form. If you choose a large asteroid, or even a moon, it will just feature a very large cataclismic explosion (way, way larger than what an atomic bomb would do, way larger than a dinosaur-killer) and then, the asteroid will simply merge into the planet. If it is something large enough to break up a large quantity of mass of the planet, it will probably blow it up. The resulting energy will turn anything in the surface or the atmosphere in hot plasma, vaporizing also a large fraction of the mantle. There is no way for anything to survive that. Also, even with that, gravity might just coalesce everything together again or coalesce part of the material in orbit forming a set of moons (which might further collide, escape or fall down into the planet afterwards). It is possible, though unlikely, that gravity coalesce two or more different bodies in different stable orbits around the central star, but no life could ever survive that.

Whatever you do to separate the two planets, if the resulting planets features oceans, orbit their stars in goldilocks zones, are able to hold significant atmospheres for a few billion years (unlike Moon, Mercury or Mars), and don't get runaway global warming due to greenhouse gases (like Venus did) they probably would be able to regenerate life.

The only way I see for something as complex as plant and animals survive splitting up the planet in 2 or more pieces, is if it is done by the most boring and simple way possible: Grab a piece of the rock/mantle/core from the planet and put it in orbit somewhere nearby. Grab another piece of rock/mantle/core and put it together with the first one, with gravity taking the task of glueing them together. Repeat those steps some trillions times until you got two different planets. Whoever is doing that would probably be very capable of caring about plants, animals or whatever else they want to preserve.

About binaries planets, that might be possible, Earth-Moon is often cited as an example, but Pluto-Charon is probably a better one. For trinary planets of similar size, this seems to be unlikely since there would be too much gravitational pertubation (3-body problem). However, if they are habitable moons around a gas-giant planet, or just planets in separate orbits around a single star there is no problem with that. You might also end with co-orbitals, like the saturnian moons Janus and Epimetheus.

Another possibility could be to put a planet in the L4 or L5 point of the other one, but this only works if one of them is way larger than the other, otherwise, the smaller body will librate enough until it get free from the lagrangian point, and soon smash into its larger pal.

  • 1
    $\begingroup$ So if nothing else, this has all gotten me thinking. Abstractly to say the least. If the advanced being made use of the megalaser and quickly followed up with a gravity reversing "device" or "energy" (and I'm acutely aware I'm now in the realm of science fantasy) the resulting planetoids may theoretically be capable of drifting apart. Relatively gently at that (at least compared to collision with a moon-sized asteroid). $\endgroup$
    – mordecai
    Jun 24, 2016 at 21:55
  • 1
    $\begingroup$ @mordecai Just remember that the resulting planetoids will try to reassume their spherical shape, and it would be very hard to ensure that this would not be a too much violent event. $\endgroup$ Jun 24, 2016 at 22:04
  • $\begingroup$ fair enough. I'll continue contemplating concepts. End result may be too good to pass up not to fudge the genesis a bit. $\endgroup$
    – mordecai
    Jun 24, 2016 at 22:09

There are inherent issues with what you are proposing. Splitting the planet into three parts, leaves none of the planets with enough mass and resulting gravity to maintain an atmosphere. The process also exposes and divides the planet's rotating molten metallic core which generates our magnetic field and keeps the sun from cooking us. Each of the smaller planets would therefore be unable to sustain life.

Since you have added advanced beings to the mix, none of those problems are unsolvable, but as we are not yet advanced beings, I have no details on how they would do it.

Here is an out of the box idea which sort of obeys the laws of physics as we know them...

  1. Remove all life from the planet and store it somewhere safe.
  2. Cut the crust into multiple pieces and raise each part into low orbit.
  3. Bring in some asteroids, melt and accelerate them and add them to the core to increase its mass and magnetic field.
  4. Bring in more asteroids and build a new crust around the bigger core, insulating it while maintaining/increasing its spin and resulting magnetic field.
  5. Lower each of the original crust parts back down until the gravity on their surface matches their original gravity, then build up the crust below them (with more asteroids) to hold them at that height.
  6. Add more atmosphere till each of the now chasm separated crust parts has breathable air at standard pressure.
  7. Add enough momentum to the planet along its orbital vector so that the new heavier earth doesn't fall into the sun.
  8. Put all the life back where you found it.

This wouldn't divide the world into different planets, but it might provide isolation and intimidation effects which your world splitting act was looking for.

  • $\begingroup$ Had to read your post like 4 times, but it has been helpful. I do want the density and atmosphere of each new planetoid to vary. But I have thoughts on how to create more density, magnetism and atmosphere. I'd say it might be reasonable to assume each question presents it's own problems, but that question 2 is kind of the major issuse. No surface life would survive this process no matter how you slice it. (pun sort of intended). Might have to dip into the supernatural realm here. :( haha $\endgroup$
    – mordecai
    Jun 24, 2016 at 21:31

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