I recently finished playing Alien: Isolation (which I assume is not canon). Near the end of that game, you have to go on a spacewalk, and some xenomorphs follow you outside.

Alien: Isolation final EVA sequence scripted event

I've heard some people claim this is a plot hole, because (in real life) no living thing can survive in space unprotected.

But when I watched the original Alien movie, it seemed like the xenomorph was functioning more or less normally during the brief period after Ripley ejected it from the shuttle but before the engines fried it, so I had assumed it was capable of moving around in a vacuum (at least for a little while) without any serious harm.

However, when I went back and rewatched that scene just now, I couldn't tell whether the xenomorph was actively grabbing onto the hull or just bouncing around because the harpoon in its torso was still connected to the shuttle, so maybe I was imagining things.

Alien 1979 xenomorph shuttle scene

So the question is: What canon evidence do we have about how well xenomorphs can or cannot function in the vacuum of space, or how long they would survive in it?

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    I found this neat article about humans. Apparently we could remain conscious for ~15 seconds. I would assume the xenomorph is more resilient (still assuming, which is why I won't answer) Aug 4, 2015 at 21:03
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    I checked the script for Alien, but it's probably too different from the final movie to be of much help. It describes the creature's "tentacle" getting stuck in the airlock door and it squirming around outside until "Roby" turns on the "ram jets" to incinerate it.
    – Ixrec
    Aug 4, 2015 at 21:16
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    Fun fact: At least one living thing can survive in space: Tardigrade. From Wikipedia: Tardigrades can survive in extreme environments. For example, ... the vacuum of outer space. :)
    – kjw
    Aug 4, 2015 at 21:59
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    @kjw - Damn it, you beat me to the Tardigrade reference. My greatest wish is to have a pet giant, black bear-sized Tartigrade. I would sell my car and ride the water bear everywhere I went.
    – Wad Cheber
    Aug 4, 2015 at 22:35
  • @WadCheber - Haha that would be awesome! Yea ever since I learned about the indestructible tardigrade I have been a fan.
    – kjw
    Aug 4, 2015 at 22:39

4 Answers 4


I hate to be a stick in the mud, but the answer is quite unequivocally "it depends". (I'm not even sure "canon" evidence applies here, since you're referring to a plot hole.)

It depends on so many factors that the physiology of the particular xenomorph would need to be known to make a prediction.

Home planet atmospheric pressure

If the creature evolved on a large planet (more gravity, higher atmospheric pressure), it may have evolved a stronger skeleton in order to maintain mobility - or even compensated with a strong exoskeleton instead of or in addition to an internal one - which might lead one to believe that it would withstand a vacuum better (less deformation at 0 atmospheres.) But if the creature has a vascular system (which is common in multicellular organisms), it has evolved under the same conditions as the skeleton: at a higher atmospheric pressure.

Microgravity has the largest effect of the space-flight environment on human physiology; all organ systems are affected to some degree. Acclimation during space flight: effects on human physiology

The problem with vascular systems in space is that the unbound dissolved gas comes out of solution at the sudden lowering of atmospheric pressure - exactly like having "the bends".

For a creature accustomed to a higher atmospheric pressure, the result of being in space would be more dramatic, not less.

If the creature evolved under a lower atmospheric pressure - say, a smaller planet or at a higher elevation than sea level - they would do better. This is why sherpas do better at higher altitudes than their non-sherpa counterparts on the mountains: they've evolved mechanisms to deal with lower atmospheric pressure (and therefor lower oxygen levels). Their blood vessels are more expandable than their non-sherpa counterparts, so there is less cerebral and pulmonary edema as well.

If you put a European from sea level and a sherpa into space, a sherpa would stay conscious marginally longer than the European. (Humans stay conscious - kind of - for 10-12 seconds in a vacuum.)

Since the creature in Alien seemed to thrive in the same conditions as humans, I'd guess their adaptability to a sudden vacuum would be about the same (though tissue swelling seen in humans might not appear because of their partial exoskeleton).

And this is taking only one aspect - dissolved gasses in the vascular system - under consideration. It doesn't take into account gas filled spaces - like lungs or intestines.

It depends on the xenomorph: their home planet size, their vascular systems, their cellular structure, etc. It all matters.

Evolving altitude aptitude
If you don't know about Joe Kittinger, you should; he is a phenomenonal person. He went into space in a pressurized suit in a balloon, before astronauts, to help study the effect of high altitude on pilots who faced emergency ejections. His glove was damaged and he had to duct tape his wrist, which cut off circulation in space. Though his hand swelled, it returned to normal.

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    There's also the theory that the xenomorphs were artificially created/altered as bio-weapons, which would remove evolutionary constraints from the equation. I personally find that theory very plausible as there are many other things about the xenomorph which don't make much sense in terms of evolution.
    – Ixrec
    Aug 5, 2015 at 6:37
  • @Ixrec - ah, I had forgotten that tidbit. Good point. I assumed "xenomorph" applied to all ectraterrestrial, not just to the creature in Alien. Again, good point, but the laws of physics demand to be obeyed by both biological entities and mechanical ones. Aug 5, 2015 at 6:42

Microorganisms can actually survive in space as the Russian and American spaceships found out, more complex organisms...not so much.

  • There is a class of bacteria called extremophiles which are able to survive all kinds of conditions extremely hostile to life.

  • Even conventional bacteria can be extremely resistant to hostile conditions if they organize into biofilms.

  • There are many case studies about panspermia indicating that life not only can survive, but propagate in space.

More complex organisms are much more a problem. The first and foremost problem is the vacuum, an organism needs to maintain pressure if it contains fluids because otherwise the fluids will boil off and/or freeze (see below). Even humans can maintain consciousness for some seconds and our skin is resistant enough to maintain blood pressure, but it will kill us in short time.

Now if the alien is moving, it needs energy. We generate energy by inhaling oxgen, "burn" stuff (it is lower temperature, but it is really no difference to burning) and exhaust carbon dioxide. No oxygen => no energy available => we cannot move. We can use that for the xenomorph anatomy. So if the xenomorph need to breathe, even if it is able to withstand vacuum and hold their breath for a long time, their energy will rapidly deplete and they won't be able to move anymore. The only thing to avoid that is to have some kind of energy storage, but their strongness and agility works against that, they will need too much energy to maintain a sufficient storage.

The second problem is freezing (if the spaceship is far away from the sun). In space there is no heat conduction or convection, so any object will give off heat radiation and cool rapidly (The energy loss is proportional to the fourth power of temperature, so cool objects are cooling at a much lower rate than hot objects). The alien will not be able to prevent that, so being in space for a longer time will freeze everything inside and the alien is neutralized.

One possible strategy for the alien is to hibernate: Shut down the own life functions and use a protected mechanism to revive if the temperature rises again. Normal cells of complex organisms will retain irreversible damage when unfreezed, but as a biological weapon it is possible that the alien has something like that.

  • Saying "I cannot breath so I cannot move" is a huge simplification - even children can hold breath and live just fine, free divers can hold breath for minutes. And then you have sea creatures that can do it for hours...
    – Yasskier
    May 11, 2016 at 1:44

I mean if the facehugger was able to survive the incredibly hazardous planetoid while they were dragging Kane back to the ship, one can assume the final life cycle of this creature is more resilient and has higher adaptability. The species responsible for the xenomorphs supposedly harvested the best aspects of species all over the galaxy(if not universe). It is a bio-organic lifeform similar to cell from dbz. I don't see it surviving the vaccum of space that unbelievable.

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    To start an answer with "I mean" is a little odd. And "one can assume the final life cycle of this creature is more resilient and has higher adaptability." Than what? "The species responsible for the xenomorphs..." Who are they? Engineers? They "supposedly harvested the best aspects of species all over the galaxy(if not universe)?" Source? Wait. Did you just compare the Xenomorphs to Dragon Ball Z? May 11, 2016 at 1:49

Since the Xenomorph has Molecular Acid as blood it is conceivable that it directly oxidizes whatever it consumes. This oxidative reaction is generally exothermic, and as such could provide the necessary energy to survive without requiring too much oxygen. Since this oxidation would provide free protons, these could be used for the direct reduction of ADP to ATP (When the third phosphate is removed from ATP, you get ADP), assuming the Alien uses a similar molecular encapsulation of energy as creatures on this planet.

From a 'resistance to decompression' perspective, the Xenomorph should do pretty fine due to it's armored body. Let's not forget that Xenomorph have evolved to be very adaptable to many different environmental conditions, so even from this point of view they should be able to resist space vacuum very well compared to other species.

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    " Let's not forget that Xenomorph have evolved to be very adaptable to many different environmental conditions, so even from this point of view they should be able to resist space vacuum very well compared to other species." Evolution occurs in a niche, not in a lot of niches simultaneously. What is your support for your statement? Aug 5, 2015 at 6:40
  • I disagree. Evolution does not occurs in a niche. Disregard humans. From a biological p.o.v. they devolved recently (they are dumber, have less strength and are more sick). Xenomorph are probable to be present in different environments (getting there via species they implant) so their primary evolution must be based on adaptability to a very variable environment.
    – Overmind
    Aug 6, 2015 at 7:28
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    Um... Evolution certainly takes place in a niche. While this is true, you're proposing your opinion as fact. "Devolving" is a very, very slow process. I'd encourage you to check your science. Aug 6, 2015 at 14:43
  • Yes, it's a slow process but it happens. Those are facts. Example: news.yahoo.com/blogs/sideshow/…
    – Overmind
    Aug 7, 2015 at 5:51
  • Just some advice: don't get your "facts" from blogs, and brush up on your science. "I know this is true" is not the same thing as a fact. Aug 7, 2015 at 7:16

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