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In this video,

If you look closely, you can see the smaller planet deforming before the actual collision. I think I remember a term existed for this. I think it is similar to Spaghettification, but for just normal planets and similar objects. Maybe it's called 'X distance,' where X is some word I cannot remember or could be something else.

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    – Rory Alsop
    Commented Nov 19, 2023 at 22:32
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    – Zombo
    Commented Nov 19, 2023 at 22:44
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    – Rory Alsop
    Commented Nov 20, 2023 at 14:19

2 Answers 2

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The generic term is tidal deformation. At a distance of ~385000 km, the Moon subtly distorts the shape of the Earth. Those distortions are readily visible in the Earth's oceanic tides, and not quite as readily visible in the Earth's solid body tides (but still quite observable with good instrumentation). The Sun also causes tides on the Earth, about half as strong as those caused by the Moon.

These tidal distortions can in some cases rip bodies apart. A nice example was comet Shoemaker–Levy 9, which was captured by Jupiter, then later ripped apart into at least 21 pieces, which then collided with Jupiter in a well observed series of events. The comet eventually fell well within Jupiter's Roche limit, thereby causing it to be torn into pieces. Even more extreme cases involve relativistic as well as Newtonian distortions. As noted in the question, this extreme form of tidal distortions results in spaghettification.

The Roche limit is an approximation of the distance to a strong gravitational source at which a smaller body might be torn apart by gravity. If a body is composed of small particles that are bound together by self gravitation only, tidal distortions might well rip the body apart if it gets too close to a strong gravitational source.

Comets are loosely connected chunks of smaller pieces of ice and minerals that are collectively bound together mostly by gravity. The smaller pieces of comet Shoemaker–Levy 9 were bound chemically as well as gravitationally; this is why I called the Roche limit an approximation. The 21 (or more) smaller pieces remained intact until they collided with Jupiter's atmosphere.

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Could you be thinking of the Roche limit? From the link:

In celestial mechanics, the Roche limit, also called Roche radius, is the distance from a celestial body within which a second celestial body, held together only by its own force of gravity, will disintegrate because the first body's tidal forces exceed the second body's self-gravitation.[1] Inside the Roche limit, orbiting material disperses and forms rings, whereas outside the limit, material tends to coalesce.

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    $\begingroup$ @user22859957 there's a checkmark button for accepting answers $\endgroup$
    – Erin Anne
    Commented Nov 16, 2023 at 6:08
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    $\begingroup$ Hi @user22859957 - please click on the checkmark button next to the post that best answers you - that moves it to the top and ensures future visitors will see the correct answer first. $\endgroup$
    – Rory Alsop
    Commented Nov 16, 2023 at 11:49
  • $\begingroup$ The Roche limit is a radius, not a concept like "deformation due to gravity". This answer is semantically off. Also it's just a copypaste. $\endgroup$ Commented Nov 16, 2023 at 21:44
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    $\begingroup$ @AtmosphericPrisonEscape OP has confirmed twice, in comments since deleted, it was what they were trying to think of. I don't need to write a short paper on the definition of the Roche Limit to help someone remember a word. $\endgroup$
    – Erin Anne
    Commented Nov 16, 2023 at 21:49
  • $\begingroup$ @user22859957 please don't keep posting the comment, at the very least so you don't keep sending it to my inbox (which is where comments on my answer end up). I'm not deleting your comments, I don't particularly agree with the mods doing it, but all I've tried to do is help. $\endgroup$
    – Erin Anne
    Commented Nov 17, 2023 at 20:04

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