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

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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

From what I read, it’s atmosphere Is being blown away, about the same rate as earth, but it doesn’t seem to have much effect…

Another thing is the amount of co2 in the atmosphere, Venus hasn’t had oceans in a long time… on earth, the oceans absorb the co2 and make it into limestone… Venus can’t do that so the co2 just stays in the atmosphere…

Another is there’s not enough knowledge of impact and volcanic history of that planet to know how they contribute (apparently Japan has a probe looking now)

That probe has found that the ionosphere reacts with the solar wind itself, creating a magnetic field that both pushes the wind away and pushes the atmosphere back to the planet

More work needs to be done to understand fully

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.

Volcanism probably plays a major part. Venus seems to have active volcanoes; the sulfur and carbon dioxide that is found in the atmosphere quite probably came from them, as volcanoes on earth put out the same materials.

As you point out, Venus doesn’t have a magnetic field to keep the solar wind from stripping the atmosphere. Either this means that the output of volcanic gasses is able to compensate for losses, or that Venus’ current atmosphere is not stable over the long term. It is very possible that in billions of years the atmospheric composition of Venus will look very different.

The pressure/density of Venus’ atmosphere is very high at the surface, in fact it is not even a gas but a supercritical fluid, walking on Venus would be half similar to swimming! The height of the atmosphere doesn’t necessarily have a linear relationship with the density at the surface, because it is 90x higher pressure at the surface doesn’t mean the atmosphere reaches 90x as high. Gas compresses, so as you pile more gas into the atmosphere, the atmosphere sags under its own weight.

Venus has a much thicker atmosphere than Earth does. The truth is, magnetic fields are vastly overrated in importance when it comes to holding in an atmosphere. Gravity is more important. Venus (and Earth) have enough to hold on to heavier gasses. Hydrogen can be lost, and on Venus probably most of the hydrogen _has_ been lost over the eons. On a hot planet like Venus, water can get way up into the upper atmosphere, get split into hydrogen and oxygen, and then the hydrogen can be lost. Over time this eliminates most of the water on the planet. But carbon dioxide is too heavy to be lost in this way and doesn’t get broken up as easily as water. On Earth, most of the water stays safely stuck in the lower atmosphere.

As for why Venus has so much more CO2 than earth, it’s because on Earth, CO2 is constantly being trapped and buried. Of course, life does this in massive quantities, but so does the geology of our mountains and oceans. We have a Venus’ worth of carbon trapped up in carbonate rocks (limestones and the like).

Without oceans (and life or plate tectonics) Venus has nothing mcuh absorbing CO2. So it eons of CO2 production from volcanoes just build up and up, forming a thick atmosphere much more massive than the one our planet has.

You dont have to go very far underwater on Earth to get 90x the normal surface pressure at sea level.

Venus atmosphere is too hot for water to condense out and it contains lots of CO2 so it’s more like a boiling thin soup than an atmosphere.

Thin soup is still pretty thick compared to regular Earth air, so it doesn’t have to be super deep or super heavy to add up to 90x normal earth air pressure.

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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

From what I read, it’s atmosphere Is being blown away, about the same rate as earth, but it doesn’t seem to have much effect…

Another thing is the amount of co2 in the atmosphere, Venus hasn’t had oceans in a long time… on earth, the oceans absorb the co2 and make it into limestone… Venus can’t do that so the co2 just stays in the atmosphere…

Another is there’s not enough knowledge of impact and volcanic history of that planet to know how they contribute (apparently Japan has a probe looking now)

That probe has found that the ionosphere reacts with the solar wind itself, creating a magnetic field that both pushes the wind away and pushes the atmosphere back to the planet

More work needs to be done to understand fully

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.

Volcanism probably plays a major part. Venus seems to have active volcanoes; the sulfur and carbon dioxide that is found in the atmosphere quite probably came from them, as volcanoes on earth put out the same materials.

As you point out, Venus doesn’t have a magnetic field to keep the solar wind from stripping the atmosphere. Either this means that the output of volcanic gasses is able to compensate for losses, or that Venus’ current atmosphere is not stable over the long term. It is very possible that in billions of years the atmospheric composition of Venus will look very different.

The pressure/density of Venus’ atmosphere is very high at the surface, in fact it is not even a gas but a supercritical fluid, walking on Venus would be half similar to swimming! The height of the atmosphere doesn’t necessarily have a linear relationship with the density at the surface, because it is 90x higher pressure at the surface doesn’t mean the atmosphere reaches 90x as high. Gas compresses, so as you pile more gas into the atmosphere, the atmosphere sags under its own weight.

Venus has a much thicker atmosphere than Earth does. The truth is, magnetic fields are vastly overrated in importance when it comes to holding in an atmosphere. Gravity is more important. Venus (and Earth) have enough to hold on to heavier gasses. Hydrogen can be lost, and on Venus probably most of the hydrogen _has_ been lost over the eons. On a hot planet like Venus, water can get way up into the upper atmosphere, get split into hydrogen and oxygen, and then the hydrogen can be lost. Over time this eliminates most of the water on the planet. But carbon dioxide is too heavy to be lost in this way and doesn’t get broken up as easily as water. On Earth, most of the water stays safely stuck in the lower atmosphere.

As for why Venus has so much more CO2 than earth, it’s because on Earth, CO2 is constantly being trapped and buried. Of course, life does this in massive quantities, but so does the geology of our mountains and oceans. We have a Venus’ worth of carbon trapped up in carbonate rocks (limestones and the like).

Without oceans (and life or plate tectonics) Venus has nothing mcuh absorbing CO2. So it eons of CO2 production from volcanoes just build up and up, forming a thick atmosphere much more massive than the one our planet has.

You dont have to go very far underwater on Earth to get 90x the normal surface pressure at sea level.

Venus atmosphere is too hot for water to condense out and it contains lots of CO2 so it’s more like a boiling thin soup than an atmosphere.

Thin soup is still pretty thick compared to regular Earth air, so it doesn’t have to be super deep or super heavy to add up to 90x normal earth air pressure.