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Should larger rocky planets eventually crack due to temperature difference between their layers? When a tick piece of glass is left to cool down it would eventually crack...but this is caused dominantly by interaction with atmospheric gasses.In the case of a planet there is only an interaction with free space in the form of electromagnetic radiation.But could this radiation reduce temperature so quickly to cause a large temperature gradient through planet layers so that the colder outer layers crack as they shrink in volume quicker then the inner layers?

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When hot enough, rocky minerals can slowly creep and deform plastically when stressed, without cracking. So rocks that seem brittle and crack-prone can actually flow (slowly!) like taffy in hot places like the earth's crust to produce masses of solid rock which are folded all the way through 180 degrees- without liquefying.

So it is unlikely that a rocky planet with a hot core would develop cracks going all the way through it; it would instead deform and flow.

However- closer to its surface, where the temperature is too low to support creep, cracks will develop- as they do on earth, where those cracks are called faults.

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The specific fracture mechanism of glass requires high stress throughout a single piece. It seems unlikely to me that such a configuration would be possible over a large area of a planet. Instead multiple fragments would exist, and those could move relative to each other without causing further fractures.

The moon's crust is cracking as the moon cools, but it is not due to differential temperature stress or the shrinking of the outer crust. Instead, it is because the solid outer crust is supported by the cooling and shrinking interior. As the interior shrinks, the outer crust collapses. The now smaller sphere must have a smaller surface area and this happens via faulting. https://www.nasa.gov/press-release/goddard/2019/moonquakes

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