Only certain planets (like ours) actually have a liquid core with a solid outer crust. Most rocky planets are like Mars, completely solid all the way through.

I believe what the other commenter was getting at is that, on large scales, the solids that make up planets behave like liquids do at smaller scales. Since if you zoom out, there's not much different between a bunch of rocks loosely held together with gravity and a water droplet weakly held together by surface tension.

[–] tomiant@piefed.social 3 points 19 hours ago* (last edited 19 hours ago)

Could this object that drive-by slammed into Earth be the source of the iron for that molten iron core we have or did the Earth already have it?

[–] Womble@piefed.world 7 points 1 day ago (2 children)

Even if they are "solid" at a human sized scale they are effectively liquid on a planetary scale. Gravity is just so much stronger than the internal stiffness at that scale that they behave as if they are a liquid with effectively no interal stiffness. That's why as you get smaller down to moons and asteroids you start to se shapes that arent spheres, the materials strength has sufficient strength to be able to resist gravity at those scales and the material is acting more like a solid.

[–] absGeekNZ@lemmy.nz 3 points 7 hours ago

Gravity is so weak, that the electromagnetic force (the one that determines solid/liquid/gas) can resist its influence until you get to planetary scales.

Mountains can only exist because of the utter feebleness, of gravity.

To overcome the coulomb barrier; to achieve nuclear fusion; you need a stars mass of material forcing the nucleons together.

As you said, "at that scale", which is totally correct. I'm just trying to ensure that anyone reading this doesn't get the impression that gravity is strong compared to the other fundamental forces.

[–] tomiant@piefed.social 2 points 19 hours ago

Whoa.