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

Venus’s atmosphere has more pressure because there is more of it: the mass of Venus’s atmosphere is about a hundred times the mass of Earth’s.

Largely this is just a fluke of how we define “atmosphere”, distinguishing between liquids and gasses. If we considered liquids to be part of a planet’s atmosphere, we’d describe the two planets as having similar atmospheric mass. And if we considered Earth’s surface to be the floor of the ocean rather than the top of the ocean, we’d describe the two planets as having similar surface pressure.