What makes Venus’ atmospheric pressure so high at its surface?

Question

I’ve been reading that Venus’ atmospheric pressure is something like 90x Earth’s…but since Venus’ gravity is almost identical to ours and with no magnetic field to keep the solar wind from stripping the atmosphere from the planet, what makes and keeps it so thick? How does it not just evaporate or blow off into space (if being continuously fed by volcanoes) to make it closer to Earth’s density under Earth-like gravity?

**Edit:** Thanks to all of you who took the time to answer here; I think I finally understand what’s at play and how it works. Made my night, and you’re all awesome, hey? 🙂

In: 11

Answer 1

Higher pressure with the same surface gravity and the same size simply means more atmosphere. Pressure at ground level is essentially a measure of the weight of the air above you. Venus’s atmosphere weighs 4.8×10^(20) kg, 93 times more than the earth’s which weighs 5.15×10^(18) kg. Venus is 5.3% smaller than the earth so the surface area is 10.8% smaller, meaning that much more air per unit area. Against this, Venus’s gravity is only 90.4% of the earth. Combining these numbers gives:

93×110.8%×90.4%=93

This closely matches estimates of Venus’s surface pressure in units of earth-standard atmospheres.

Answer 2

Higher pressure with the same surface gravity and the same size simply means more atmosphere. Pressure at ground level is essentially a measure of the weight of the air above you. Venus’s atmosphere weighs 4.8×10^(20) kg, 93 times more than the earth’s which weighs 5.15×10^(18) kg. Venus is 5.3% smaller than the earth so the surface area is 10.8% smaller, meaning that much more air per unit area. Against this, Venus’s gravity is only 90.4% of the earth. Combining these numbers gives:

93×110.8%×90.4%=93

This closely matches estimates of Venus’s surface pressure in units of earth-standard atmospheres.