Darren asks:

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 -273^oC) 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 100^oC 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.

 ——————————————————

1. 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.
2. 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.

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Topical science time! This recent news article caught my eye the other day. Russian scientists have succeeded in drilling through the 3.7 km thick layer of ice covering Lake Vostok in Antartica and hope to be able to extract samples from the lake later this year. Lake Vostok has been completely sealed off from the surface for about twenty million years. This makes it a very interesting place to look for life forms, and what they’re doing in Lake Vostok right now is not a million miles away from the way we’ll likely find the first alien life forms.

The environment inside Lake Vostok is, to put it mildly, just a little bit exotic, and not the first place you’d expect to find bacteria. The ice sheet covering it is so thick that we didn’t even know for sure that there was water down there until aircraft- and space-based radar picked it up in the early 90s. Because it’s got a 3.7 km thick ice layer sitting on top of it, that water is under a tremendous amount of pressure – enough so that it remains liquid¹ despite having an average temperature of -3^oC. This high pressure also results in that water being supersaturated with high concentrations of oxygen and nitrogen than you’d find in an equivalent surface lake, much of which has been forced into “cages” of water molecules called clathrates. There is no light at the bottom of Lake Vostok, but that’s okay because there’s no light at the bottom of the ocean either and we find plenty of stuff living – in fact, thriving – down there, most of which tends to cluster around geothermal vents on the ocean floor – and we suspect the same might be true of Lake Vostok.

Not that you particularly need a geothermal vent to support life these days. Hopefully you’ll have heard of these guys – the extremophiles. Over the last few decades we’ve kept finding them in locations which were thought to be completely inhospitable to life – too hot, too cold, too acid, too alkali, too saline, even too radioactive. In all of these places extremophiles thrive, and some of them even need those harsh conditions in order to survive; for example the halophile loves salt and can’t grow without at least a reasonably high concentration of it present in its surrounding environment.

This has completely revolutionised our view of the conditions required for life to exist, and it’s entirely possible that at the bottom of Lake Vostok there will be a colony of extremophiles that has been evolving entirely on its own for the last 15-20 million years, and which has adapted to exist in the freezing, oxygen-rich environment down there. If they do exist, then those extremophiles will be completely unlike anything we’ve so far observed; bear in mind that twenty million years ago the ancestors of the human race looked something like this and then consider what those twenty million years of divergent evolution might do to bacteria. If they’re down there, and the Russians do find them, then it’ll be as close as we can get to finding alien life without actually going to another planet to do it.

What does this mean for the chances of alien life existing? Well, it improves them considerably, at least in terms of micro-organisms — you might not be able to have a conversation with one but you can at least be comforted that somewhere out there in the Milky Way is the alien equivalent of a tardigrade. However, it also improves the odds of us, personally (or at least a probe controlled by us) going out into space and actually digging some of these things up. You see, Lake Vostok isn’t the only place in the Solar System where there’s a large quantity of water trapped under several kilometres of ice. Several of the moons of the gas giants also qualify; notably Europa, Ganymede² and Callisto.

Europa is the really interesting one. The surface of Europa is entirely composed of ice, making it by far the smoothest body in the Solar System, but we think that ice surface is only 10-30 km thick. Beneath that is a layer of conducting fluid – overwhelmingly likely to be saltwater – that was detected by the Galileo probe via its magnetic moment. This water is kept relatively warm by tidal heating³ provided by Jupiter, and it’s possible, although nobody knows exactly how possible, that there might be microbial life down there living in environments similar to the ones we find extremophiles inhabiting on Earth – in cold, dark environments like the bottom of Lake Vostok, or next to deep sea thermal vents that spit out heat from the moon’s interior (it does have radioactive decay heating, although this is deemed insufficient to create the subsurface oceans). Missions to visit Europa to try and find some of this life have been mooted for years, although I don’t believe any of the proposals have satisfactorily tackled the question of how exactly you drill through ten kilometres of ice on another planet with a robot probe when it’s taken the team at Lake Vostok decades to bore through four kilometres with the benefit of having humans on hand to operate the equipment. Regardless, it’s likely that it’ll be tried sooner or later depending on what future technology does or does not render possible, and so if you’re unlucky enough to be alive seventy or eight years from now you might end up having the news of the first discovery of alien life piped into your brain through your neuro-cortical machine interface.

The other possibilities are somewhat less interesting. Ganymede has an ice-silicate lithosphere over 200 km thick covering its ocean, so it’s doubtful we’ll ever be able to tunnel down there. Callisto too has a surface layer up to 150 km thick. Enceladus on the other hand is kind of promising; if you’ve watched that EXPLETIVE DELETED Brian Cox on his EXPLETIVE DELETED EXPLETIVE DELETED series Wonders of the Solar System, you’ll be aware that Enceladus has a surface which, like Europa, is composed entirely of ice, but that Enceladus is unique in that the Cassini probe observed water vapour outgassing from the surface in 2008. This points to the presence of liquid water in some form or other, the most likely source of which is yet another subsurface ocean – and since it’s outgassing directly from the surface, it points to this ocean being somewhat more accessible than that of Europa (after all, it needs some way to get there from the interior). At the very least it should be possible to collect material that has come directly from the ocean and determine its composition, and thus its likelihood of being able to support life. While Enceladus isn’t necessarily a better bet for finding life than Europa, it’s potentially far more useful for telling us what the odds of that bet actually are.

The first step, though, is to look at these subsurface water environments on Earth. The Lake Vostok team has been painstakingly drilling through the ice for years while constantly at the mercy of the Antarctic elements (Lake Vostok is the coldest place on Earth). They used a thermal sensor to detect when they were approaching a source of free water and stopped the drill, the general idea being that the decrease in pressure would allow the ice separating the borehole and the lake to melt and then refreeze; they can then retrieve this portion of ice to examine water that has come directly from the lake. Meanwhile they’ve examined the last piece of ice extracted from the borehole – which contains ice thought to have frozen onto the bottom of the ice sheet hundreds of thousands of years ago – and they’ve managed to turn up evidence of extremophile microbes, so the odds are good that there’s a colony of something down there. The team has plans to go even further by sending a robot down in late 2013 to retrieve samples from the sediment making up the lake bed. I suggest you pay attention to the results, if only to make sure that this hasn’t happened.

1. If you think back to the geophysics post you’ll recall that the normal rules of physics don’t really apply when you crush something underneath hundreds of millions of tons of pressure. Rock cannot melt despite being at a high temperature because melting would require it to have some room into which it can expand – and because it’s compressed so much by the high pressure, this is the one thing it doesn’t have. Because water is unusual in that it actually expands in volume upon freezing into ice, the same rule applies to Lake Vostok.

2. CORRECTION: I stated in the geophysics post that Earth is the only body in the Solar System known to have a liquid iron core. While this is broadly correct, it is also suspected that Ganymede, Venus and Mercury might have them as well; Ganymede is very uncertain, Venus is likely based on its similar size to Earth (with the absence of plate tectonics being explained by there being no water on the surface of Venus to soften up the crust enough to allow plate formation/subduction) and Mercury has a strong magnetic field relative to its size which also points to the existence of a partially liquid core. Tectonic behaviour is observed on many of the icy moons of the gas giants, but their tectonics all involve chunks of ice shifting around and not rock. Earth is still a unique case in terms of the strong magnetosphere and plate tectonics.

3. Ever seen a picture of Io? I don’t particularly recommend it as a holiday destination because it’s absolutely covered in volcanoes. In terms of raw geological activity it puts the Earth in the shade, but unlike the Earth this is entirely down to outside forces: tidal heating caused by a constant tug of war on Io between Jupiter and the other Galilean moons which constantly squeezes and stresses it like… well, like somebody constantly squeezing and stressing a stress ball. Io has to relive this internal pressure somehow, and it does it by forming volcanoes which constantly spew out poisonous sulphur gas, which has stained the entire planetary surface a sickly yellow colour.

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