eli5: Why has Venus’ atmosphere so much more pressure than Earth’s atmosphere?

Question

There must be some factor other than gravity that contributes to an atmosphere’s pressure level because Earth and Venus have almost the same mass.

In: 3

Answer 1

There’s simply more mass in Venus’ atmosphere, which doesn’t affect the mass comparison between the two planets because the mass of the atmospheres are insignificant in comparison to the mass of the planets involved. Venus’ atmosphere is also composed of almost entirely Carbon Dioxide, which (as a triatomic molecule) is going to hold a lot more heat than what you’d see in the mostly diatomic nitrogen and oxygen molecules that compose Earth’s atmosphere.

The other big contributor is Venus’ proximity to the Sun, meaning they get more heat, and thus will have a higher temperature.