Pawel Garycki
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What would be Venus surface temperature at 90bar if the atmosphere were composed on N2/O2 as on Earth, without near 100% CO2?
How much CO2 accounts for the 462C on Venus surface and how much it is the pressure, radiation, albedo?
 
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Matthieu Fontaines
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The Greenhouse Effect - why the surface is so hot

The Atmosphere

The atmosphere is 96.5% CO2 and with virtually no water (very different from Earth).

The surface pressure is about 90 times higher than on Earth. At this pressure, CO2 is highly absorbing both at 15 microns and near 5 microns = 5000nm. With a surface temperature of about 730K, by Wien's law the emission peak is close to 5000 nm.

Greenhouse effect on Venus

The sunlight is mostly at wavelength of~ 0.6 microns = 600nm, which is not absorbed efficiently in CO2 , so the sunlight scatters its way through the clouds and eventually makes it to the surface. It warms the surface and the surface then radiates in the infrared. However, the CO2 absorbs the infrared radiation and it does not all escape into space, but much of it is trapped between the surface and the CO2 layers in the atmosphere. The end result is that the surface heats to 730K - only at this high temperature is it possible for the energy to escape at the same rate it is absorbed by the surface. By Wien's Law, at this temperature much of the energy is shorter than the CO2 absorption at 4000 to 5000 nm, so it can escape and stop further heating of the surface. (From Germantown Elementary School, http://www.germantown.k12.il.us/html/Venus.html)

This process makes the atmosphere incredibly hot and maintains the high surface temperature.

Any water originally on Venus has boiled into the atmosphere and been broken apart by ultraviolet light from the sun. The hydrogen has escaped so water cannot form again. Venus has lost almost all water.

Water is key in controlling the greenhouse effect on Earth: (1) the oceans absorb a lot of CO2 (2) water and CO2 react with silicate rock to lock the CO2 up in carbonaceous rock; and (3) water nourishes plants, which remove CO2 from the atmosphere. When Venus lost its water, it was no longer able to suppress atmospheric CO2 and was doomed to develop an extreme greenhouse effect.


this is for the second part of your question.

For the first part, you may have to propose a these on the subject, not sure the answer is available anywhere
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Pawel Garycki
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The end result is that the surface heats to 730K - only at this high temperature is it possible for the energy to escape at the same rate it is absorbed by the surface. By Wien's Law, at this temperature much of the energy is shorter than the CO2 absorption at 4000 to 5000 nm, so it can escape and stop further heating of the surface. (From Germantown Elementary School, http://www.germantown.k12.il.us/html/Venus.html)

So does that equilibrium 730K depends on CO2 alone or are there other factors in the calculation of that output, e.g. atmospheric pressure. I guess one of the input is solar radiation, the other is atmospheric composition. As the surface heats because of some solar radiation, also an albedo plays the role. Perhaps the equation formula is a difficult one.
Why do I ask? Because on gas giants there are also high temperatures and pressures deep in the atmosphere (e.g. at 22 bar there is 153C) but the atmospheric composition and received sunlight is different. So some heat must come from pressure alone.
This is a valid question for Venus terraformation. How much can we change atmospheric composition on Venus and how much should we remove the atmosphere to lower pressure in order to lower the surface temperature, and possibly how much should be shade the sunlight with mirrors.
 
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Pawel Garycki
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Btw. the link is dead: www.germantown.k12.il.us/html/Venus.html
 
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Matthieu Fontaines
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While I have some interest in science, I am neither an exoplanet or climate expert, I just did dig this website for you... I hope someone on the forum will be able to answer you, though it may be a step ahead of current human knowledge...

concerning the dead link, blame the author of the website :)
And after all, this is just the source for what the author is writing... So most of the data is in the website itself it seems

anyway good luck, I keep the website open, but don't know if I will really read it ;)
 
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There some info on Wikipedia about terraforming Venus:
https://en.wikipedia.org/wiki/Terraforming_of_Venus

Specifically they say:
Quote:
More recent research has however shown that the current slow rotation rate of Venus is not detrimental to the planet's capability to support an Earth-like climate. Rather, the slow rotation rate enables the formation of thick cloud layers on the side of the planet facing the sun, which raises planetary albedo and acts to cool the global temperature to Earth-like levels, despite the greater proximity to the sun. According to calculations, maximum temperatures would be just around 35 °C, given an Earth-like atmosphere.
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Pawel Garycki
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abdiel wrote:
According to calculations, maximum temperatures would be just around 35 °C, given an Earth-like atmosphere.

Thank you.
And now may somebody find the Earth-like atmosphere but with 90 bar pressure.
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Nick Zube
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improove wrote:
abdiel wrote:
According to calculations, maximum temperatures would be just around 35 °C, given an Earth-like atmosphere.

Thank you.
And now may somebody find the Earth-like atmosphere but with 90 bar pressure.


Yep, this is why terraforming on Mars won't be happening any time soon in the real world. Within reasonable financial means (under several trillion dollars), there's nowhere to get, transport, protect (there's no magnetic field to shield charged particles from the sun) or make the components of a 1 bar N2/O2 atmosphere on Mars.

It's a total mass of ~5x10^18 kilograms on Earth, and doing the same calculation to find the amount needed to create 1 bar pressure on Mars gives a result of about 1/10th that, which is still a LOT of material.
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