A hypothetical planet is 2/3 the radius of earth but has 1g surface gravity. Given the planet has the same surface gravity as earth, the atmospheric pressure would be the same. This would also mean there is less atmosphere in terms of mass on my planet. Would this also mean the atmosphere on my planet has the same scale height ? How high is my planet’s atmosphere compared to Earth's ? What other consequences would there be for my planet's atmosphere due to the planet’s size ?

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    $\begingroup$ This seems to be more suitable for Worldbuilding than here $\endgroup$
    – Kyle Kanos
    Commented Dec 20, 2023 at 0:01
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    $\begingroup$ I’m voting to close this question because it belongs to the World building site. $\endgroup$
    – Miyase
    Commented Dec 20, 2023 at 1:03
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    $\begingroup$ Note that escape velocity is reduced by a factor of $\sqrt{2/3}\approx 0.8165$, which makes it easier for atmosphere molecules to escape. $\endgroup$
    – PM 2Ring
    Commented Dec 20, 2023 at 6:13
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    $\begingroup$ You can't predict atmospheric height or thickness from the planet's gravity or size. For example, Venus has a much heavier atmosphere than Earth, despite being slightly smaller. You should probably also compare Earth's atmosphere to that of Titan - a moon, not a planet, much smaller than Earth, but with a greater surface atmospheric density than ours. $\endgroup$
    – J.G.
    Commented Dec 20, 2023 at 8:40
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    $\begingroup$ Voting to reopen. I have removed the references to D&D, which leaves a perfectly clear physics question about the atmosphere on a hypothetical planet. $\endgroup$
    – gandalf61
    Commented Dec 20, 2023 at 12:17

1 Answer 1


Atmospheric pressure on a planet tends to scale with gravity since gravity is what allows it to hold particles in, but there's no a priori reason it would have to have Earth's pressure. Venus is roughly Earth's size but has 100 times the pressure.

Density will scale with potential energy, so that $N(h) \sim N_0 e^{- gh}$ where h is the height above the surface and $N_0$ is the density at sea level.

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    $\begingroup$ No mention of temperature. $\endgroup$
    – ProfRob
    Commented Dec 20, 2023 at 8:17
  • $\begingroup$ @ProfRob ok . . . . $\endgroup$
    – Señor O
    Commented Dec 20, 2023 at 23:37
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    $\begingroup$ $gh$ is not dimensionless, so your equation makes no sense. What matters is the ratio of gravitational potential energy to thermal energy $\mu gh/k_BT$. $\endgroup$
    – ProfRob
    Commented Dec 20, 2023 at 23:57
  • $\begingroup$ So just say the exponent should be that instead of a vague "no mention of temperature"? Or edit it yourself? The question is just asking about how gravitational strength and planet size fit into the question. $\endgroup$
    – Señor O
    Commented Dec 21, 2023 at 3:19

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