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Let's take a planet with an atmosphere as dense as Venus, where there are extremely high winds far above the ground, but it's fairly tame at the surface itself. Perhaps the clouds are made of a nicer material. Is there any distance from a star we could place this planet where it could support life?

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    $\begingroup$ Not certain the question can be answered in reality. The state of Venus as it exists now, the composition of its atmosphere, ratio of CO2 etc is highly dependant on where it formed in our solar system and how much energy it receives from the sun. Not to mention habitability questions we simply do not know. For example technically Venus is within the "goldilocks zone" but yet there are strong arguments stating that life on Earth would be impossible without the accident of our Moon. IF Venus had our Moon would it be habitable? Maybe. $\endgroup$
    – Gillgamesh
    Apr 16 at 16:24
  • $\begingroup$ Do you need life at the surface, or could also be something higher up in the atmosphere work? (I guess, technically humans likely could live like 90 km above the ground on current Venus, if they have oxygen and something to stand on.) $\endgroup$ Apr 16 at 23:15
  • $\begingroup$ @Gillgamesh -- I'd recommend you work that into an answer, as it's really not just a comment. $\endgroup$
    – elemtilas
    Apr 16 at 23:53
  • $\begingroup$ The overwhelming factor that keeps Venus from being habitable is its weak magnetic field. Our magnetic field makes most of the solar wind go around us. Without it, the solar wind would dissociate hydrogen from high-altitude water, and we'd lose all of our hydrogen to space. At the moment, all of the hydrogen in Venus's atmosphere, if converted to water, would fill a big swimming pool, but that's it. $\endgroup$ Apr 17 at 18:25

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Habitable for humans? Probably not. For other things? Sure, why not.

Lets assume you've handwaved away the inconveniently hot air, and unpleasant atmospheric mixture. You're still left with a surface pressure of more than 90 bar.... that's the equivalent of more than 900m underwater on Earth.

Some experimental work has been done on deep saturation diving on Earth, back before uncrewed underwater vehicles became as capable as they are now. The record sits at a little over 700m in the COMEX Hydra X program (a simulated depth in a hyperbaric chamber, but close enough to a habitat on your benign Venuslike). Further work has not been done because robotics is just safer and cheaper, but even if it weren't, human biology just doesn't work that well under such pressures. The best breathing gas mix made so far, hydreliox, still has some inert gas narcosis issues at depths below 500m and the addition of hydrogen can delay the onset of high pressure nervous syndrome but never completely eliminate the risk.

There are also some more exotic issues, like the fact that hydrogen and oxygen at that pressure aren't strict gases anymore, but supercritical fluids, and that suggests the density of the stuff you'd be breathing might be unpleasantly high, which makes breathing harder and ridding yourself of CO2 harder too.

So, even if the temperature were benign, the pressure very much isn't and so the environment would only be habitable for heavily modified humans, or humans inside submarine-like protective habitats and vehicles where the internal pressures are much closer to Earth surface normal.

Clearly though, life can and does work just fine on Earth at those depths ... elephant seals and beaked whales can dive to below 2000 m, and the only reason to do that is to eat things down there. Black smokers have been found at depths of 5000 m. Clearly life can thrive, but you probably couldn't.

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  • $\begingroup$ The mountains of Venus go down to 47atm (about 450 m), quite a bit less than the 700m COMEX experiment. Presumably a human could live their whole life at 47atm, but long-term problems are a possibility. $\endgroup$ Apr 16 at 19:38
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    $\begingroup$ @KevinKostlan living your whole life at 47 atm is easy. Having it be more than a year seems trickier. $\endgroup$ Apr 16 at 20:44
  • $\begingroup$ Depth is not that big a problem - humans can adapt to it quite easily. It's ascending that is difficult. Hydreliox eases the issues of descent and ascent. HPNS doesn't occur in saturation divers which spend months at deep pressure. So if you're healthy and willing to spend a year to gradually descend to "colder Venus", pressure won't be the main issue. $\endgroup$
    – Therac
    Apr 16 at 21:41
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    $\begingroup$ @Therac no, humans cannot adapt to it quite easily, it causes a whole host of physiological problems. Humans certainly do not spend substantial periods of time at depths over 500 m where hydrogen narcosis is a problem. Humans do not generally spend months at several hundred meters at all... deep saturation dives tend to be at most one month, singular. $\endgroup$ Apr 17 at 15:06
  • $\begingroup$ We don't know the long term consequences for years at 500m in H2+He+O2. Keep in mind that confinement to a tiny prison itself is very harmful, so general symptoms of feeling unwell, if they indeed do appear over time, could be just that. $\endgroup$ Apr 22 at 2:40
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I am generally not a fan of comments where the conclusion is: If you want it to be so in your world just make it that way. However in this case, as the question is asked it is probably the only real answer.

Any other answer presumes we know far far (really far) more about planetary habitability, formation/genesis of life, planetary chemistry, etc etc (allot of etc.) than we actually do. As I alluded to in my comment to the OP, there are far too many variables to say anything but "Maybe?". We have ideas why Venus is hot windy dry and a miserable place all around but we do not know.

On Earth, we have a myriad of unique properties that have all led to life as it exists, the only way we know it exists and again, do not fully understand. Some elements my be crucial, some may be dispensable for a short time. The absence of some may only allow microbes to exists and nothing more complex.

Some examples like plate tectonics. Are tectonics necessary for a magnetic field? necessary to counter erosion witch would eventually wear down the planet to a smooth ball and retard evolution. and deplete available minerals on the surface. Earth’s Tectonic Activity May Be Crucial for Life—And Rare in Our Galaxy

The Moon regulates our seasons, Earths spin and tilt. It could have a large effect on plate tectonics, affects the tides witch in turn contributes to erosion distribution of nutrients across the globe as well as climatic patterns and water cycle. Not to mention how many hits by rogue asteroids has the Moon taken, saving earth from ELE impacts. Did we need the moon for life?

Just by moving Earth to a different orbital position would it still be habitable? Any honest answer you get no matter how verbose and how attributed it is would boil down to, shrug... maybe?

If you moved Venus farther away from the sun when it formed and that's all, would it be habitable? Maybe it would have had a better chance at being habitable. That change at its beginning could have changed the whole chain of events that lead to the state it exists now. But if you want it to be so, then say it is and move on.

PS: his may be a helpful resource: Planetary habitability

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Stephen H. Dole, in Habitable Planets for Man (1964) discussed the atmospheric mixes which were tolerable for humans.

And since that time more work has been done with testing dense air mixes for deep diving under high pressure. Perhaps modifying Dole's conclusions.

The inert dilutent gases which Dole believed could be breathable in the highest concentrations were argon and helium, and there are qusiton marks with those upper limits. Much work has been done with using helium in diving mixes since then.

Hydrogen has also been used in diving mixes. So there should now be some informatin about the upper limits for hydrogen pressure. A hydrogen-oxygen mixture also has to be non flammable.

Thus it should be possible to calculate the maximum possible pressure of a human breatheable atmosphere and how it compares to the surface pressure on Venus.

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You live on a Venus-like planet that is further from the Sun.

Venus and Earth are pretty much twins, with Venus being just 5% smaller, and Venus never having undergone whatever process formed the Moon - thought to have been a collision. In the early days of the solar system, the atmospheres of Earth and Venus were pretty similar. Most likely, the difference in solar radiation was an important reason in why they diverged and life was able to take hold on Earth and not on Venus, although some have suggested an important role for the Moon.

Once you have life, you don't have a Venus-like atmosphere

Earth has the atmosphere that it does because of the presence of life. Over several billion years, the oxygen generated by life first oxidised the rocks and oceans, and then transformed the atmosphere into the one we know today, with life eventually evolving oxygen-based respiration and using that atmospheric and dissolved oxygen to power their metabolisms.

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In theory. The atmospheric pressure of 90 atm is equivalent to depths of 900 m under the Earth's ocean, and life lives there. Perhaps on this high-pressure world, the terrestrial creatures have any hard structures made of substances with enough compressive strength to survive this pressure, even though most terrestrial organisms would have completely soft bodies with hydroskeletons.

However, life would have it a lot easier in the upper atmosphere, where the high atmospheric density supports larger flying organisms. Perhaps these upper parts of the atmosphere with a more Earthlike atmosphere have creatures that live their entire lives gliding on the winds, eating aeroplankton like whales.

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