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So "Venusians" are these Star Trek-y humanoid aliens that evolved on a planet with more than 75 times Earth's atmosphere. In a lot of ways this makes them not too dissimilar from deep sea creatures. Their bodies combat the extreme external pressure of the atmosphere with ludicrously high internal pressure to keep them from imploding. So how come they don't just... y'know... blow up in our own atmosphere? Sure, they could wear suits but where's the fun in that?

The whole point of having aliens adapted to extreme pressure is to have them inflate in a comical way in our atmosphere of course! Who wouldn't want to laugh in the face of an alien who looks and sounds like a blobfish on helium? Anyway...

Venusians, believe it or not, look just like human actors that wear lots of make-up and latex prosthetics to cover their noses and other defining facial features like hair or ears. While they look normal in their native atmosphere their bodies become extremely bloated in ours, their skin flushes with pink blood and their voices sound as if a rubber duck met an air hose. All these things are set in stone. Any other anatomical features that would allow them to transition from a dense oxygen rich atmosphere to another is still up in the air (pun not intended).

Earth-like planet

Pressure: 93 bar (1,350 psi)

Temperature: hot

Recommended activities: hiking and slow skydiving

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    $\begingroup$ "Dense oxygen rich" atmosphere does not allow such creatures to survive in Earth atmosphere due to partial pressure of oxygen there being way higher than 1 atm. Therefore they are obligated to wear suits in order to maintain internal oxygen pressure at least at half as high as on their planet. $\endgroup$
    – Vesper
    Commented Apr 23, 2023 at 5:13
  • $\begingroup$ I also wonder if a creature that evolved in such pressure would still have an anthropomorphic form. The reason I think that blocks that is winds. A wind under 93 bar pressure is 93 times stronger than here, so if ever there is a wind of 10 m/s, it'll carry enough impulse to break or knock down almost any creature. Avoiding being tossed around would certainly require a different form than a human-like one. Maybe down to a turtle-type shape. The island of Inaccessible does not have large animals, so it's quite hard to find an Earthly analogue for a shape for extreme winds. $\endgroup$
    – Vesper
    Commented Apr 24, 2023 at 3:31
  • $\begingroup$ 75 times Earth's atmosphere - So, a Gas Giant? [Clippy]: Did you mean Earth's atmospheric pressure?? $\endgroup$ Commented Apr 24, 2023 at 15:48
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    $\begingroup$ their bodies combat the extreme external pressure of the atmosphere with ludicrously high internal pressure - Every single creature does this, from birds to the abissal fish on Earth. And the internal and external pressures are usually the same. $\endgroup$ Commented Apr 24, 2023 at 15:50
  • $\begingroup$ If you neglect breathing, humans can likely survive in 100 atm of pressure. Most of our body is incompressible. Only cavities like our sinuses, eardrums, and lungs are damaged by high pressure. If your Venusians can breathe a liquid, they would be set. Or if they can survive breathing a ~1 atm gas, they should be fine in our atmosphere. $\endgroup$ Commented Jun 21, 2023 at 15:18

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Their Internal Body Pressure can Reduce When in Lower Pressure Environments

Perhaps these aliens have a way of decreasing internal body pressure. They aren’t able to completely acclimate to Earths atmospheric pressure because it’s so much lower, but Earth’s low pressure only causes some swelling in their bodies. Perhaps it could work based off body fluids, and when they are initially exposed to far lower atmospheric pressure, their body releases fluid through sweat gland type pores in their skin. After their internal body pressure gets within a ratio to atmospheric pressure, the body just has some swelling that won’t go away. When reintroduced into higher atmospheric pressures, their bodies rapidly produce these “body pressure fluids” to build their internal pressure back up. I hope this helps you.

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    $\begingroup$ After putting some thought into this, I think you got it. To avoid rupturing the cell membranes a Venusian's cells would pump out the extra water with Vacuole-like organelles. That same water is then stored in-between the body's tissues until the pressure increases again. So a Venusian's bloated appearance is actually sacks of water being filled... wow. That actually did help! Thank you! $\endgroup$ Commented Apr 23, 2023 at 17:40
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    $\begingroup$ @LiveInAmbeR No problem! I’m glad I could help you out! 👍🏻 $\endgroup$
    – Kal Madda
    Commented Apr 23, 2023 at 17:46
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    $\begingroup$ Also: Decompression chambers exist. It may be a multi-week or even several-months affair to get them to "earth-level pressure", like human saturation divers, but in reverse $\endgroup$
    – Hobbamok
    Commented Apr 24, 2023 at 7:48
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    $\begingroup$ See "because that's not how physics works to begin with". Liquids and solids don't really compress, it is the dissolved gasses coming out of solution that creates problems with decompression. Picture dissolved CO2 forming bubbles in your soda pop as soon as you release the pressure being held in by the cap. That's what nitrogen does in your bloodstream if you decompress to rapidly. The body doesn't explode, and by the time any comedic bloating is observed the subject would be dead. $\endgroup$ Commented Apr 24, 2023 at 17:26
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Because that's not how physics works to begin with

From a physical standpoint, humans do just fine at higher pressures. The deep diving record is around 600 meters, where the pressure is equal to about 60 atmospheres. We survive at these depths by having a very high internal pressure that keeps us from being smashed into a little ball, just like a Venusian! Theoretically, the only issue with going deeper is that basically all the gases become poisonous to us at too high of pressures. And naturally, these deep divers did not explode when they returned to the surface.

Venusians don't explode when they go from 75 atmospheres to 1 atmosphere for the same reason humans don't: liquids and solids are perfectly happy to operate over an extremely high range of pressures without any significant deformation.

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    $\begingroup$ deep divers do need to ascend slowly to avoid exploding when they return to the surface. $\endgroup$ Commented Apr 24, 2023 at 12:42
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    $\begingroup$ @user253751 Would they actually "explode", or just have the nitrogen bubbles form in the bloodstream? I remember a movie scene where someone smashes a window on a pressurized room and the person in it exploded, but I thought that was just for the rule of cool and gore. $\endgroup$ Commented Apr 24, 2023 at 15:45
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    $\begingroup$ no, they don't explode, that was an exaggeration. They do need to ascend slowly so they don't die. Maybe from a great enough depth you could make one explode. I'd suggest not trying that experiment. $\endgroup$ Commented Apr 24, 2023 at 15:45
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    $\begingroup$ @LiveInAmbeR - no, that doesn't help with the fundamental problem of depressurization. Venusians would cope with 75 atmospheres or 1000 atmospheres in exactly the same way human divers cope with ascending after pressurizing to 60 atmospheres: By very slowly venting internal compressible organs that contain gas like ears and lungs, and very, very slowly and carefully outgassing dissolved gasses like oxygen, CO2, and nitrogen in fluids. Humans and whales and fish and, presumably, Venusians don't have the ability to remain pressurized at more than a few kilopascals, they all equalize. $\endgroup$
    – johannes
    Commented Apr 24, 2023 at 16:30
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    $\begingroup$ @LiveInAmbeR I think the core concept here is that liquids and solids don't change all that much with a change in external pressure. It's gases which are affected by pressure. Whether that's dissolved gasses or internal gas chambers which aren't connected to atmosphere. Therefore, you can strike a balance between desired effects and undesired ones by judiciously changing how much gases are involved. e.g. Venusians swell not because their solid organs are doing so, but because they can't properly regulate tiny gas chambers (like sinuses) in their body. $\endgroup$
    – R.M.
    Commented Apr 24, 2023 at 20:43
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Frame Challenge

Well, sort of...

The Venusians have an extremely dense outer skin and musculature system that works in their native Venus to resist the Pressure of their own atmosphere, despite the high internal pressure.

However, when they get to earth, that same Skin and Muscle design actually help to keep the internal pressure in.

Now for story elements you could have something like this isn't comfortable and that they can't do it for too long as the stress on the muscles causes fatigue - but this would give you a semi-plausible way to have them going around without a suit on - by having a muscle system that can withstand the pressure.

Alternatively - you could look at the physiology of say a deep-water Giant Squid/Colossal Squid - they live approximately 1 Km under the sea, which has a pressure of ~100 Bar, yet examples have been brought to the surface (and viewable at Te Papa in New Zealand) - and do a little handwavium along the lines of 'they have adaptations similar to those of deep-sea dwellers to handle extreme pressures' and leave it at that.

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    $\begingroup$ The Colossal Squid (and complementary whale skeleton) was the best thing the embarassing glorified video game parlour called Te Papa ever displayed. They actually have the first ever ID'd dinosaur fossil (an iguanadon thumb), but never display it, although they display 1980s biscuit tins. The Colossal Squid was first class, though, including in presentation. $\endgroup$
    – user86462
    Commented Apr 23, 2023 at 2:20
  • $\begingroup$ I found it pretty painful when the internal pressure of the swelling was contained by my skin. Mobility (and the blood flow) was also restricted. That would be beyond just uncomfortable. Muscle strength isn't the issue here. Deep sea creatures don't need " extremely dense outer skin and musculature system". $\endgroup$
    – gre_gor
    Commented Apr 25, 2023 at 5:57
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Their home planet has a wide variance of pressure

While they prefer being at high pressures, their native environment includes higher up 'skies' which are lower pressure, low enough for them to swim up to hunt. As such they have a number of adaptions to let them transition from one pressure to another.

That said, rapid transitions do make them look more puffy and drunk. To safely transition they need a few hours.

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  • $\begingroup$ I see you got the hiking hint. +1 $\endgroup$ Commented Apr 23, 2023 at 17:26
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The only part of your question that might have an answer relates to pressure.

Just consider the problem of traveling from an environment with an atmospheric pressure of 93 Bar to an environment with only 1 Bar pf pressure as an exercise in 'reverse' deep sea diving. Your Venusians 'might' (depending on their physiology) be able to survive such a change by simply using the equivalent of commercial deep sea diving chambers to slowly equalize the difference in pressure over time. After a number of days inside the chamber they can emerge on Earths surface. When they want to go back 'up' to their normal pressure they simply re-enter the chamber and reverse the process.

The problems you can't fix however are the differences in atmospheric composition and temperature between Earth and Venus. A creature evolved to exist in an atmosphere of almost pure CO2 and sulfuric acid instead of water vapor plus an average surface temperature of 475C will not be able survive on the surface of the Earth without some form of insulated space suit any more than humans could survive on the surface of Venus without one.

So sorry, if you really want Venusians walking around 'bare skinned' on the surface of the Earth your only option is to say it's just 'magic'.

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  • $\begingroup$ According to the question, they aren't literally from Venus, it's just the name given to them in this work because they come from a planet with similar atmospheric pressure (but not similar atmospheric composition). $\endgroup$
    – Idran
    Commented Apr 24, 2023 at 14:23
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    $\begingroup$ I re-read the question. Yes it does that that the planet has an oxygen rich atmosphere. But it also states that its hot. The thing is they're still a life form evolved to exist at 96 bar in a hot climate. That means they still wont be able to survive on Earth without an environmental suit. (The same thing applies to us visiting their world.) Also humans can't survive at temperatures at or near freezing for long without thick protective clothing. The aliens would be just as badly off - our 'normal' would be their arctic/cold. They'd also need a respirator/gas mixers like deep seas divers use. $\endgroup$
    – Mon
    Commented Apr 25, 2023 at 2:28
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As long as they don't boil or sublimate, Solids and liquids don't really change much with pressure, and gasses are mostly found in the lungs, as long as the pressure change is gradual they will vent. The lack pressure won't directly make them blow up.

However that doesn't mean the pressure won't cause them problems.

  1. Their vocal cords were intended to operate in much higher pressure, i'm not sure what effect the lower pressure will have. I know lower density at the same pressure results in higher frequency but i'm not sure if the same is true of lower density as a result of lower pressure.
  2. They may struggle to get enough oxygen (or whatever), this may cause various physiological problems.
  3. They may have issues with substances "boiling out" of their tissues. Human deep sea divers have this problem with nitrogen if they resurface too quickly, but maybe the aliens have some other volatile substance in their bodies that can't be eliminated in a reasonable span of time.
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    $\begingroup$ The "high-pitched" sounds humans make when we breathe helium are because the speed of sound is different in helium than in air. In air, the speed of sound doesn't depend much on pressure, so changing pressure doesn't really change much at all. Divers can still talk in a diving bell and fighter pilots can still talk at 45000 feet. $\endgroup$
    – Chris
    Commented Apr 25, 2023 at 17:16
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Hyperventilation causes a Pufferfish like Stress Response.

Many other answers have already explained how divers can make this kind of transition; so, your Venusians should be able to survive the transition as well, but they don't do a good job of explaining why Venusians become and would stay puffy since a transition period should negate any puffiness before they actually enter our lower atmosphere. Instead of treating it as a pressure issue, treat it as a reflexive action. When puffer fish get stressed, they fill up to a large size to make it difficult for predators to get thier mouths around them. Likewise, your Venusians likely have some ancestral predators that they evolved a similar countermeasure against. So, in thier own environment, puffing up is quite a normal thing, but only when they are panicked.

However, just because a Venusian can survive at way lower pressures does not mean they are meant to breath our air. Our atmosphere is about 21% oxygen at 1 bar, but maybe your Venusians have a native atmosphere that is about 0.5% oxygen at 75 bar. While this puts the total oxygen in our air at close enough to Venusian levels that they don't just suffocate, it will still leave them oxygen deprived forcing them to breath rapidly.

This rapid breathing triggers something akin to a sympathetic nervous response just like humans get when we are oxygen deprived which makes the Venusian feel anxious and reflexively puff up.

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  • $\begingroup$ In humans, rapid breathing isn't caused by the lack of oxygen, but excess CO₂. $\endgroup$
    – gre_gor
    Commented Apr 25, 2023 at 6:21
  • $\begingroup$ @gre_gor Technically true... but saying that would be misleading in this context. It is the excess CO₂ in our bodies caused by not having enough O₂ in the air that triggers hyperventilation. But extra CO₂ in the air does not make us hyperventilate. This is why hikers hyperventilate at high altitudes even though the CO₂ in the air around them is lower. $\endgroup$
    – Nosajimiki
    Commented Apr 25, 2023 at 16:01

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