i have seen similar questions but not exactly what am looking for.

what i want to know is if the planet would stay as a planet rather than tearing it self apart into large separate chunks.

i know its orbit will change but but i need to know if its possible not to get pulled into the star or crash into into another planet and just survive in its new orbit long enough for for another species to discover it millions of years later and possibly finding evidence of what happened.

EDIT : to add more clarity the world in my story has a fusion between magic and technology and supernatural beings/gods also exist. one of the gods is actually the core of the planet its not the usual core though thats just its body, any function/effect that a regular planet core had it could also copy using magic and it formed/built the planet around it self as shell for protection and later teleported away (leaving vacuum in its place) to escape from danger

  • 1
    $\begingroup$ Welcome to Worldbuilding SE! It's an interesting question, but we could use some clarity: How large is the planet and what is it made of? Is it like Earth or a gas giand? How large a fraction of the planet disappears, just the inner core, inner and outer core (if we assume an earth like planet) or part of the mantle as well? Is it instantaneously replaced with a vacuum, or changed into something else? The reduction of mass shouldn't throw it totally out of orbit, but depending on how it happens and how much is left it might more or less "explode". $\endgroup$
    – EdvinW
    Dec 6, 2020 at 13:58
  • $\begingroup$ @EdvinW hello ! the planet is earth like and the inner core replaced with a vacuum. i edited my question to add a bit more clarity hope it helps $\endgroup$
    – Dyno
    Dec 6, 2020 at 14:11

2 Answers 2


Presumably, the core vanishes due to magic, super-powers, or something else that escapes from the normal constraints of physics?

In any case, the newly-hollow planet will not stay that way. It will collapse into a smaller, solid planet, and the released gravitational potential energy will likely melt all of the remains.

Its orbit won't change dramatically. If it were orbiting its star by itself, its orbit would hardly change at all. Given that its mass has been reduced by the disappearance of its core, its influence on the orbits of other planets in the system will be reduced, and that may indirectly alter its orbit a little, but the change won't be large. The kinetic energy and angular momentum of the core vanished along with the core, as the OP added. If the planet has a moon or moons, their orbits will be changed by its reduced mass, and if they didn't orbit close to it, they may escape.

A few million years later, another species finding it will be puzzled by this planet. It will seem to have formed more recently than other planets in the system, because its surface has been molten more recently (this is easily discoverable via radiometric dating). Its density will also be lower than would be expected, because of the way that dense materials get concentrated in the core during the normal formation of planets. An obvious explanation would be that it had been hit by a rogue planet, but its orbit will not be plausible for that to be the cause. If they think of the core "just vanishing," they're unlikely to take that idea seriously unless they know of previous cases.

  • $\begingroup$ thanks for answering! yes the core vanishes due to magic as clarified in my edit and the knetic energy and angular momentum vanish along with the core. $\endgroup$
    – Dyno
    Dec 6, 2020 at 14:14
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    $\begingroup$ If the planet has a moon, that moon will now be less attracted, so it likely gets a larger orbit, or in the extreme case can even escape. $\endgroup$ Dec 6, 2020 at 21:51
  • $\begingroup$ Can you expand on how Newton's Shell Theorem interacts with this. $\endgroup$
    – lijat
    Dec 6, 2020 at 23:02
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    $\begingroup$ @PaŭloEbermann For a circular moon orbit, if half (or more) of the mass of the planet vanishes, the moon is going to escape. For the elliptical situation, it depends on the specifics of the orbit and the position of the moon when it happens; Nearer periapsis, you don't need as much mass to vanish for an escape. Nearer apoapsis, you need more of the mass to vanish. $\endgroup$
    – notovny
    Dec 7, 2020 at 0:17

Going point by point:

not to get pulled into the star or crash into into another planet

That's relatively simple, and what would happen in our Solar System for most – if not all – of the terrestrial planets. Orbital parameters depend on the force of gravity, and that force, in turn, depends on the relative masses of the bodies involved - if one body possesses most of the mass (like our Sun, with 99% of the system's mass) , and everything else in the system is "sufficiently" far away, the planet will be still there in millions of years.

finding evidence of what happened

As John Dallman's answer notes, this is not very likely. But from your comments I think you need to understand why.

Picture a planet without its core:

coreless planet

We've previously established that gravity is an Important Thing™ when dealing with planetary bodies. Well, "nature abhors a vacuum". All those little bits and pieces of the outer core, mantle, and crust are now attracting each other:

coreless planet-forces

in other words, your coreless worlds will be crushed because there's nothing within it to prevent otherwise, with immense forces eradicating any surviving evidence.

Given the setting, your solution must involve some kind of "ghost force" essentially propping up the rest of the planet from doing just that.

  • $\begingroup$ A note for anti-nitpicking: yes, the diagram is simplified, and shows only (some of) the dominant forcess - the planet will not collapse simply towards the center, there will be also significant attraction "laterally". For anything on the surface that does not wish to become part of a subduction zone, this is, however, an academic difference. $\endgroup$
    – mikołak
    Dec 6, 2020 at 21:58
  • $\begingroup$ SHINEI KAKYOIN! $\endgroup$ Dec 7, 2020 at 5:18

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