This pops up in video games relatively frequently, and I’ve often wondered: would it actually be possible for an organism to evolve in (or evolve the capability to survive in) the vacuum of space? If it’s possible at all, what qualities would they need to have (or what qualities would be especially beneficial) and how complex could such organisms realistically become?
As you’ve touched on, the answer to this one depends on two things.
1) What you mean by “vacuum”.
2) What you mean by “organism”.
As it stands each one could potentially describe a rather large number of variable states, so we’re going to have to narrow down a bit.
First I should make it absolutely clear that the chances of something that we’d recognise as life evolving in situ in the vacuum of space are bugger-all. There’s simply too many missing elements that we regard as being necessary for life to evolve in the first place; no gravity, very little energy, no nutrients, none of life’s basic building blocks, nothing. It’s kind of like saying “Can life evolve out of nothing inside a blast furnace?” Well no, probably not. Organisms which start out in more temperate environments can evolve to tolerate very high temperatures (as covered in my extremophiles post), and this is the great power of evolution: it’s a gradual, iterative process in which organisms can adapt to live in just about any kind of environment imaginable, but they need to begin that process in a place which is conducive to life forming in the first place.
So here we’re covering the second case, in which we start out with some bacteria or something swarming and multiplying inside a primordial ooze. If we were vengeful gods (or the typical consumer of Maxis games) and we could somehow tinker with the evolution of this bacteria over hundreds of millions of years, could we end up with something capable of living in a vacuum? And if so, how complex could we make it? In order to save time I’ll just assume I can give our little super-organism any attribute exhibited by currently existing lifeforms; what would it take to make its survival possible?
For the vacuum, we’ll consider a single factor that determines how hostile the environment is: is there a large quantity of harmful solar radiation present that could do awful things to a cell directly exposed to it? For the organism, we’ll simply deal with the hardiest forms of life currently known to man, the various genii of extremophiles. As for what that organism is going to need to make it go, I’ll be using Wikipedia’s definition of life here. Most of it can be taken for granted (in that anything we recognise as life will have these attributes by default) but the three things we have to cover from that list are:
Metabolism. Our vacuum-dwelling organism needs to eat something to sustain itself.
Growth. It needs to take the resources it metabolises and use them in anabolic processes to grow itself. The rate of growth needs to at least match the rate at which bits of the organism are dying off, otherwise the organism as a whole will gradually shrink and eventually die.
Homeostasis. Its vital systems need to be stable and self-correcting inside the parameters of the environment it’s going to be living in. Because this is vacuum that environment is potentially very very demanding, with the temperature in particular undergoing rapid and extreme changes on a regular basis.
I should probably stress at this point that I’m a physicist, not a biologist. I understand everything I’ve told you so far because they’re fairly simple physical systems; energy intake during metabolic processes needs to equal energy spent to grow the organism, and so on. I don’t need to know the actual mechanisms behind “metabolism” or “growth” to tell you this, since even biological entities have to follow the conservation laws. However, your mileage may vary considerably when applying the following hypothetical scenario to actual biological processes since there’s almost certainly a huge amount of fine detail that I’m going to be ignorant of. What I’m saying here is, don’t actually try to grow a vacuum-dwelling super-organism based on what I’m about to tell you because you’ll probably come a cropper. It’s an interesting thought experiment and nothing more.
Metabolism and growth are intimately linked, so we’ll start with both of those at the same time. You’re not going to grow as an organism if you’re not metabolising enough matter to do so. Sadly for our prospective vacuum organism you have to metabolise something physical – for example, plants do not feed on sunlight directly but instead use the energy absorbed from sunlight to power a photosynthetic reaction that extracts carbon from CO2 and oxygen from H2O and fixes them together to form a healthy nutritious sugar. Without the carbon dioxide and the water the sunlight isn’t all that helpful; it powers the metabolic process but does not feed the organism itself. Other organisms have evolved that have substituted in other power sources to power metabolism instead of sunlight – this one uses actual honest-to-god decay radiation from natural deposits of uranium – but no matter what you use you still need something to process from the outside environment.
This is probably the primary reason why vacuum dwelling lifeforms in deep space are impossible1. There’s simply not enough raw materials out there for them to live on. Life is pretty much confined to planetary surfaces. Moreover, most forms of life require oxygen if they want to evolve anywhere useful. Wikipedia’s pages on aerobic vs. anaerobic respiration are complete garbage written by morons. Fortunately I can use my doctor skills to check sources that aren’t Wikipedia2 and I can tell you that while anaerobic respiration (metabolic processes that do not use oxygen) is fairly common at a low level within microbes and even as a temporary measure within more complex organisms (human muscles when sprinting), the amount of energy it provides is tiny compared to aerobic respiration which does use oxygen. Aerobic respiration is absolutely necessary if we want to build a complex organism, as the metabolism requirements will be so large that only supercharged oxygen molecules (which are very good electron acceptors in terms of generating energy) can fulfil them.
So this basically rules out any organism more complex than a microbe (unless they can get their oxygen from a non-atmospheric source such as an abundant supply of water, but that’s outside the scope of the question). It’s possible that alien life might evolve a decent method of respiration that does not involve oxygen, but even if it did it’d be drastically, drastically different from what we’d recognise as “life”. Since we’re now dealing with microbes there is some good news, and that’s that microbes have continually surprised us with their capacity to live and thrive in hostile environments. We’ve already seen how extremophiles have adapted to hot, cold, acid, alkali and even radioactive environments, but the thing that immediately sprang to my mind when I read this question was the curious case of the Streptococcus mitis bacteria that was (allegedly) inadvertently sent to the Moon on one of the Surveyor probes.
This bears some explanation because it’s one of the more astonishing events in astrobiology, yet it gets almost no discussion outside of academic circles — prior to me looking up that article the only reason I knew about it was an offhand piece of trivia in a Bill Bryson popular science book. Surveyor 3 was sent up to the Moon to gather scientific data and scout things out for a future lunar landing back in 1967, and it spent two and a half years sitting on the lunar surface doing precisely that. Surveyor 3 was a machine probe, not a life-bearing spacecraft. It had precisely no provision for keeping any hitchhiking microbial life alive during that thirty-month stint on the Moon. So when the Apollo 12 astronauts retrieved one of the cameras from Surveyor 3 in 1969 and brought it back to Earth, NASA scientists were rather surprised to discover about 200 spores of Streptococcus mitis hidden away inside the camera lens mounting.
Now, to be fair, there’s actually two ways this could have happened. Either common Strep. bacteria managed to survive two and a half years in an environment that is completely inimical to Earth life, or else they somehow got onto the camera at some point between the Apollo 12 astronauts retrieving it from the lunar surface and the camera being checked back on Earth. This is a debate that has sadly devolved into the scientific equivalent of “NO UR A POOPYHEAD!” Modern sceptics assert that it was sloppy procedure in the NASA clean room that lead to contamination of the camera, while the actual crew that found the bacteria cling to certain abnormalities in the way the Strep. was subsequently cultured that point to the camera bacteria being in a state of dormancy when they were recovered, which they wouldn’t have been if they’d just come out of a filthy, smelly human body. Since the original camera parts have long since been contaminated by being put on display in a museum there was no possible way to repeat the tests independently and find out for sure. If it’s true, though, then it does point to bacterial life forms being able to survive for short periods in the vacuum of space.
Unfortunately that’s not quite good enough for the purposes of our question. If the Strep. really did survive up there then it did so in a state of hibernation, shutting down nearly all active biological processes and effectively becoming inert. We want something that can live in a vacuum environment – bacteria may be able to cope in a deoxygenated environment through anaerobic respiration assuming they have a sufficient quantity of nearby raw materials, but can they deal with all that vacuum implies? This is the homeostasis part of the question: we have to set the parameters of the environment and then determine what qualities our vacuum organism would need to survive in them. I’m going to use the surface of the Moon as my touchstone here; having no atmosphere it is an almost pure vacuum and so it is exposed to all that space can throw at it including sunlight, cosmic radiation and meteorites. The things we have to consider are:
Temperature. It can get pretty cold in a vacuum, with lows in deep space approaching just a few degrees above absolute zero (or -273oC) but without an atmosphere around to filter out sunlight getting hit with the full whack of it can easily heat up the surface of the Moon to over 100oC at the equator. If you’re on part of a rotating body that alternately flits in and out of sunlight then you end up being chilled and cooked in equal measure. Extremophiles exist which live and thrive in high temperatures, and extremophiles exist which can live and thrive in low temperatures, but I’m not aware of any extremophile which can do both at once, and certainly not over a temperature range of about 250 degrees. If we could pick and choose both attributes and give them to our vacuum organism, the next thing it would have to deal with would be…
Radiation. There’s no atmosphere to filter sunlight’s UV content out, either, so our vacuum organism has to be resistant to ionising ration to boot. This is a somewhat easier condition to deal with since radioresistant extremophiles soak the stuff up like a sunbather on a hot day at the beach with nary an ill-effect in sight.
Low pressure. Not so much of a problem for certain extremophiles; this zombie microbe in particular has no problem thriving in low pressure environments (and is radioresistant to boot).
If there is a condition that would give pause to the concept life in a vacuum, then, it would appear to be the temperature range such an organism would have to endure. Still, while complex life wouldn’t have a chance in a vacuum (these adorable little water bears notwithstanding), an extremophile-type organism that could cope with it is far more plausible. It’s also worth remembering that the high- and low- temperature extremophiles are niche organisms specifically evolved to survive in a specific temperature range – in other words, the reason they can’t deal with lower/higher temperatures is because they’ve never had to. Just because an organism that can deal with both doesn’t exist doesn’t mean it’s not possible.
To sum up, then:
- Complex lifeforms cannot survive in a vacuum because they cannot derive the required amount of energy from their local environment to support their large cell structures.
- Certain forms of microbial life would be able to survive in a vacuum in the short-term, but I have significant doubts about their ability to do it over a long-term period in which the environmental parameters of the vacuum are fluctuating widely.
- It might be possible for a hypothetical microbe with all the right qualities to survive indefinitely within a vacuum. It’d certainly be foolish to rule it out just because we haven’t seen it yet; fifty years ago scientists thought the extremophile life was impossible, but today we know there are hundreds of the bastards.
Honestly though, those tardigrades scare the willies out of me and if anything is going to be able to survive long-term – if not thrive — in a vacuum environment it’s going to be them.
- I’m not ruling out the possibility of life somehow hitching a ride inside a comet or asteroid as these would provide some raw materials that could be metabolised and which would keep the organisms alive for a time.
- This is a joke, in case you’re wondering. I’m not actually going to have my sole source be a GSCE Bitesize revision page for all that it’s probably broadly correct. No, I also used the TalkTalk web… encyclopedia… hang on a minute. Seriously though, the web doesn’t appear to have a single good explanation of anaerobic respiration for idiots (i.e. me) and if any biologists are reading you should probably get right on that. Meanwhile I did ask a biologist friend if I understood it correctly and he said I was in the right general area, so that’s going to have to do.