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Back home, Venus is a twin planet with serious issues. The average surface temperature is 900 degrees Fahrenheit, atmospheric pressure is 92 times greater than ours and carbon dioxide makes up 96% of the atmosphere.

Which is unfortunate, because we actually thought Venus to be a beautiful planet, hence the name.

So let's say we reduce the amount of Venus' atmospheric CO2 from 96% to 15%, and fill in the rest with oxygen and water vapor. Would its proximity to the sun and pressure still make Venus hostile, or would it be possible for life to take hold on Venus?

note: no terraforming

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    $\begingroup$ Possible duplicate of Could we move and terraform the planet Venus? $\endgroup$ – JDługosz Oct 11 '15 at 7:33
  • $\begingroup$ This has been asked several times before. $\endgroup$ – JDługosz Oct 11 '15 at 7:33
  • $\begingroup$ @JDługosz Terraforming Venus is the question you were thinking. I never said anything about terraforming Venus. $\endgroup$ – JohnWDailey Oct 11 '15 at 14:20
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    $\begingroup$ While related, this seems like a different question to me. This is asking what would have to change for Venus to be habitable. It's a simpler question. And the answers to the other question certainly don't answer this one in any way, shape, or form. Note that sun shades would not be a valid answer to this question. It's looking for purely atmospheric changes, not mechanical ones. And it's not asking how to get there, just what would need to change. $\endgroup$ – Brythan Oct 11 '15 at 15:10
  • $\begingroup$ You actually habit venus, the upper atmosphere layer if you can build a "blimp biodome" since enough high you can get 1ATM and bit less vicius gaseous mixture $\endgroup$ – jean Nov 23 '17 at 9:35
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You can't get liquid water oceans on the surface of a Venus of any composition, and we believe we can infer that life requires liquid water on a planetary surface. Venus is too deep inside of the Sun's "goldilocks zone".

Water vapour is quite a powerful greenhouse gas. On Earth, increasing water vapour in the atmosphere is more than counteracted by increased cloud cover, which reflects enough sunlight to stop the surface temperature rising. Further in, the cloud cover would reach 100%, enough sunlight would still be getting absorbed for the surface temperature to reach 100C, and it's all over for life. Thermal runaway - the oceans boil. This will be the ultimate fate of the Earth as the Sun gets hotter, well before the Sun actually goes nova.

An Earth-sized planet in Mars's orbit might well be habitable. It's Mars's low gravity and solidified core that doomed it. (Possibly also not having a large moon to stabilize its axis of rotation, which Venus also lacks).

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The question you are asking is a bit vague. It is not clear whether you are wondering whether Venus can be terraformed, or whether you want to change its morphology as a planet altogether in order to determine whether life could have evolved on it.

If you're talking about terraforming Venus, you will still encounter a lot of obstacles. The main problem with this would be reducing the temperature from over 400 degrees Celsius to something more manageable, along the lines of 50 degrees for instance. However, the scale of this task would be enormous. In addition to this, you will need to alter the atmosphere so that it's not only breathable, but also to make sure that the levels of CO2 and sulfur dioxide are reduced enough so that the greenhouse effect is diminished. Earth itself did go through a similar state back in it's earlier stages as a planet, where volcanic activity resulted in vast amounts of CO2, however the reason it was able to sprout life forms was due to the presence of hydrogen, which is very scarce on the surface of Venus. Therefore, a "successful" terraforming of Venus might just come down to humans creating floating platforms on which they will grow whatever they need for sustenance. However, this is not a viable outcome of a terraforming process and might only be resorted to for research purposes (so those platforms would be mostly inhabited by scientists, like the research bases in Antarctica), or in the extreme case in which the Earth has suffered from a shattering cataclysm and humans have ran out of places to go to.

On the other hand, if what you're asking is whether Venus could be a planet humans could live on if its morphology had been different from the very beginning, then the answer is not so easy to pinpoint. Basically that question would come down to what factors must come together for a planet to support life forms. From then on, the question branches out into several aspects, such as: does the life on that planet have the same living requirements as life on Earth? will there be sentient life on a planet with different conditions? how would these different conditions impact the way those life forms behave and even think? So overall, if it's the second case, your question is a bit vague and you may need to do more looking into it.

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Terraforming Venus would be a Pharonic project for a Solar System spanning civilization (outside of super science like manipulating gravity or creating artificial wormholes), being orders of magnitude more difficult than terraforming Mars, or making habitable asteroids and moons around the Gas Giants.

Your specific question about insolation is the crux of the problem; Venus is close enough to the Sun to receive vastly more energy than the Earth. It is thought that any water on Venus was lost as water molecules high in the atmosphere were broken by the high energy ultraviolet radiation and the hydrogen escaped. Without some major changes, this will happen again on a freshly terraformed Venus.

The other issue is the very slow rotation of the planet. Not only will you be getting more insolation, it will be focused over a specific spot on the planet for a very long time (and over an entire hemisphere for almost six earthly months). The intense heat will lead to a pretty massive atmospheric flow pattern from the hot pole top the cold pole, and a similar pattern will develop in the hydrosphere if oceans are created.

All in all, a very difficult set of problems (and this is after you have figured out how to eliminate the 90 atm CO2 atmosphere of the planet).

The solutions would have to include somehow eliminating the current atmosphere, ramping up the planetary rotation (in either direction, Venus rotates in a retrograde direction compared to Earth and the rest of the Solar System) and charging up the planetary magnetosphere, along with deflecting some of the solar energy striking the planet. While a giant "sunshade" blocking some of the light is possible, most of the rest of the issues are simply beyond current technology.

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  • $\begingroup$ Who said about terraforming Venus? $\endgroup$ – JohnWDailey Oct 11 '15 at 14:19
  • $\begingroup$ @JohnWDailey Your question describes a process pretty similar to terraforming. $\endgroup$ – HDE 226868 Oct 11 '15 at 16:30
  • $\begingroup$ I'm not interested in terraforming. All I'm interested in is the alternate evolution of many things--plants, animals, cosmos. $\endgroup$ – JohnWDailey Oct 11 '15 at 18:19
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Yes, Venus is destined to be Hell. The reason why is all of the carbon dioxide coming from her surface. You could say that Earth is destined to be Hell, too. If our 1500 volcanoes and cars don't cause a runaway greenhouse effect and turn Earth into her "twin sister," the sun will certainly help out as it expands at the end of its life.

If you want a habitable Venus, you should probably go into the past. There's a crazy theory that Earth stole Venus's moon (which I suppose would make Earth the evil twin, and Venus the righteously vengeful one?). Another theory claims that Venus lost its moon in a catastrophic collision, the same collision that caused its unusual rotation. And Venus may have once had oceans, possibly with microbial life - although they didn't last very long.

If you're trying to create a hypothetical Venus that remained habitable into modern times, give it less vulcanism, move it farther from the sun, and let it keep its moon. When you're creating your own setting, you don't necessarily have to stick to the facts. Make Venus as earthlike as you want for your worldbuilding project, and give it roughly Earth's atmosphere (not nearly that much carbon dioxide, less oxygen, and certainly less than forty atmospheric pressures).

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Most of the CO2 on the planet has come from the crust. While Venus does have volcanic activity, it does not have plate tectonics like Earth does to recycle both water and CO2 into the crust.

Though, I do believe it would much easier than many people think but still a monumental task.

The key is to get the carbon cycle started and running enter image description here

carbonates on the surface could be harvested for hydrogen, and converted it to water, which could dissolve the CO2.

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  • $\begingroup$ Welcome to Worldbuilding, Famous Jameis! If you have a moment please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox (both of which require 5 rep to post on) useful. Have fun! $\endgroup$ – FoxElemental Jun 15 '18 at 23:15
  • $\begingroup$ This doesn't really answer the OP's question. It explains the problem with the assumptions made by the OP (which makes it a very large comment), but the OP asked... if we reduce the carbon content of the atmosphere, would the planet become habitable? and this doesn't address that at all. $\endgroup$ – JBH Jun 15 '18 at 23:16
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Earth:

Distance from sun : 93 million miles

Atmospheric CO2 : ~2%

And scientists worldwide are crying sky high to cut down CO2 discharge due to green house effect issues.

Venus:

Distance from sun : 67 million miles

Atmospheric CO2 : ~15% (in your scenario)

You do the math. As far as I think, you would rather go on a trip to Sahara in summer than Venus.

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  • $\begingroup$ Your Earth CO2 content is off. Like, ALOT off. It should be about .4%. $\endgroup$ – Pyrania Sep 4 '18 at 16:32

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