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A severely destroyed planet is a popular trope in media. Here are a few examples from fiction with pictures (spoiler warning).

  • A crater with a diameter 1/3rd the size of the planet itself:

Earth (Adventure Time) https://adventuretime.fandom.com/wiki/Earth?file=AT_earth2.jpg

  • A crater so large that nearly half of the planet is missing:

Concord Dawn (Star Wars) https://starwars.fandom.com/wiki/Concord_Dawn?file=Concord_Dawn_system.png

  • A planet so destroyed that only a sliver remains, still maintaining the crescent shape of the partial sphere:

Earth in 2091 (Marvel) https://marvelcinematicuniverse.fandom.com/wiki/2091?file=Earth.png.jpg

  • A planet cracked in half with both halves offset from each other:

Gem Homeworld (Steven Universe) https://steven-universe.fandom.com/wiki/Gem_Homeworld?file=Legs_From_Here_to_Homeworld_366.png

I know that the physical behavior of objects changes dramatically with scale, one example being the anatomical differences between insects and elephants. I would imagine, at a planetary scale, that the last three examples may just collapse back into a spherical shape because of gravity.

Could these planetary bodies actualy maintain the shape we see in fictional media?

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  • $\begingroup$ You can check pictures of Rheasilvia crater on Vesta asteroid. en.wikipedia.org/wiki/Rheasilvia. Mars is theorised to have a giant impact too, but the all we can see now - the Northern hemisphere of Mars has several kilometers lower altitude than the Southern hemisphere, in average. $\endgroup$
    – Heopps
    Sep 8, 2022 at 9:55

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The short answer is no! But the process would take time. If we imagine that some impact causes the crater at some $t_0$ in the past, then the exact time frame on which the planet would begin to warp is uncertain and would depend entirely on the interior dynamics. Assuming all of these were Earth-like planets, they would all return to some "sphere-like" shape in the far future because of the plasticity of the planet. However, if you somehow created a planet which was rigid enough to resist any inhomogeneous forces due to gravity, you could see craters like these last indefinitely. What makes planets reshape is really that they are not entirely rigid in their dynamics.

One interesting question which I cannot answer for you in any reasonable time period is whether more deformed planets would become semi-spherical faster that those that are less deformed.

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  • $\begingroup$ For all craters, one also needs to consider whether or not the planet is geologically alive or not (e.g., the earth vs. the moon) $\endgroup$
    – Justin T
    Sep 7, 2022 at 23:47
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There is a threshold case. In some geophysical situations, a body achieved hydrostatic equilibrium soon enough after its formation, and was warmer and softer. However, radioisotopes decay, bodies radiate, and mantles stiffen. Should an impact happen to a sufficiently aged body, the resulting shape could hold in some instances.

Most asteroids are small enough to be random shapes, due to collisional processing/disruption. However, the parent planetesimal may have been round (thus, semantically planet or planetoid or something) and was likely softer- possibly far softer, a colloid.

In general, though, these are smaller bodies than postulated by sci-fi sources. Reality is too sci-fi for them to make up… or they reject realities that would be too much of a stretch for audience plausibilities/sensibilities, certainly in mass-market works.

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