# Atmosphere of a hypothetical planet

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 ?

• This seems to be more suitable for Worldbuilding than here Commented Dec 20, 2023 at 0:01
• I’m voting to close this question because it belongs to the World building site. Commented Dec 20, 2023 at 1:03
• 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. Commented Dec 20, 2023 at 6:13
• 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.
– J.G.
Commented Dec 20, 2023 at 8:40
• 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. Commented Dec 20, 2023 at 12:17

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.
• $gh$ is not dimensionless, so your equation makes no sense. What matters is the ratio of gravitational potential energy to thermal energy $\mu gh/k_BT$. Commented Dec 20, 2023 at 23:57