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Is it theoretically possible that planets exist with mountains so high that their peaks overtop the planets atmosphere? And which physical laws are relevant for this question? I'm just curious. Thanks for your answers.

The question came while I imagined the atmosphere like a second ocean above our ocean of water. And I thought it would be nice if such a gaseous ocean could have islands as well.

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  • $\begingroup$ A very dense planet/moon would have a narrow atmosphere, one that doesn't go as high as those of not very dense planets. E.g. Earth is the densest planet and the significant atmosphere rises about 60 mi (100 km) up. Titan on the other hand is not dense so its significant atmosphere goes about 500 mi (800 km) up. Planets/moons that are both tiny and very dense might indeed have mountains that rise above what might be considered the space border. $\endgroup$ – John Nov 19 at 18:24
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This is a bit of a gray area, as an atmosphere doesn't have a clear boundary. That being said, Olympus Mons on Mars is so tall, the atmospheric pressure on top of it is only 12% the average pressure on the surface of Mars. That's near vacuum by terrestrial standards.

https://en.wikipedia.org/wiki/Olympus_Mons#Description

In general, for this to happen you need:

  • a pretty thin atmosphere to begin with
  • some exceptional geology that ends up producing very tall anomalies like Olympus

It's not a very likely combination, but it can happen, as seen on Mars.

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Some planets have no atmosphere at all, so every bump, hill, and mountain would meet your requirement. There's no fundamental physics that has to do with the size of mountains and the thickness of the atmosphere. They are controlled by completely different processes.

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I think the planet's size and it's geological activity will dictate the mountains height. Mars is smaller than Earth and no active core, So has high probability to have mountain like Olympus Mons.

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