How cold is space to a human?

[Sirrobert]

So I was thinking today about how objects in space have difficulty losing heat, because radiating heat is so ineffcient.

But than I started wondering: Just HOW inefficient is it actually? What scale are we talking about? (I also saw some clips from Guardians of the Galaxy, with Starlord flying around in space in just his regular clothes and a special helmet)

So my questions:

Is the cold in space actually a problem for humans? Would it be possible to survive space in just face protection? And if so, how long? What would kill you?

[sal_vager]

In the 1981 movie "Outland", starring Sean Connery, there is a scene where a construction worker in space gets a hole in his suit. As the air leaks out, the internal pressure drops and his body is exposed to a vacuum, we watch in horror through his faceplate as he swells, and explodes.

A somewhat similar scene is in the 1990 Arnold Schwarzenegger movie, "Total Recall." In that movie, Schwarzenegger leaves the pressure of the habitat of a Mars colony and begins to blow up like a balloon in the much lower pressure of the Mars atmosphere, not quite a vacuum. He is saved by the creation of an entirely new atmosphere by an ancient alien machine.

The question is, what happens to the human body in a vacuum?

No, the body won't blow up. Your blood won't boil, either.

There are a number of things about being in space, in a vacuum, which could cause harm to the human body. You wouldn't want to hold your breath. This would cause lung damage. You would probably remain conscious for several seconds, until the blood without oxygen reaches your brain.

It would be pretty darn cold, but the human body doesn't lose heat that fast, so you'd have a little time before you froze to death. It's possible you could have some problems with your eardrums, including a rupture, but maybe not. It would be worse if you had a cold, and were stuffy headed, with no way for the pressure to equalize.

You could get a bad sunburn, and you might actually swell some, but not to Arnold Schwarzenegger, "Total Recall" proportions. The "bends" are also possible, just like a diver who surfaces too quickly.

While your own normal blood pressure will keep your blood from boiling, the saliva in your mouth could very well begin to do so. In 1965, while performing tests at the NASA facility now known as Johnson Space Center a subject was accidentally exposed to a near vacuum (less than 1 psi) when his space suit leaked while in a vacuum chamber. He did not pass out for about 14 seconds, by which time unoxygenated blood had reached his brain. Technicians began to repressurize the chamber within 15 seconds and he regained consciousness at around the equivalent of 15,000 feet of altitude. He later said that his last conscious memory was of the water on his tongue beginning to boil.

The human body is amazingly resilient. The worst problem would be lack of oxygen, not lack of pressure in the vacuum. If returned to a normal atmosphere fairly quickly, you would survive with few if any irreversible injuries.

There have actually been cases of parts of astronauts bodies being exposed to vacuum, when suits were damaged. The results were negligible.

It would be pretty darn cold

[-Velocity-]

So I was thinking today about how objects in space have difficulty losing heat, because radiating heat is so ineffcient.

But than I started wondering: Just HOW inefficient is it actually? What scale are we talking about? (I also saw some clips from Guardians of the Galaxy, with Starlord flying around in space in just his regular clothes and a special helmet)

So my questions:

Is the cold in space actually a problem for humans? Would it be possible to survive space in just face protection? And if so, how long? What would kill you?

I doubt you could survive very long in space with just a face mask. You have other holes in your body- your ears, your butt, your eyes- and those need to be plugged too. The sphincter isn't going to be able to hold back the vacuum of space when it can barely even hold back a large burrito. Additionally, you might have a difficult time exhaling- because your chest is exposed to vacuum. When you load it up with air, that will be a lot of lbs per square inch pushing it outward.

However, let's say that you had just your arms and legs directly exposed to vacuum. You could probably survive like that for a fairly long time, if you could get a fairly airtight seal around them and replace any air leaking out. It probably wouldn't be very comfortable though. I believe there was an account of someone who got their entire hand exposed to vacuum for a pretty long time and suffered no ill effects at all. Your body, except for where it has holes, is reasonably well sealed.

For a more reasonable depiction of human exposure to vacuum, see 2001: A Space Odyssey.

There are a few inaccuracies with that scene however; for one, the gasses released from the hatch expand too slowly; secondly, there would be some "sound" when the gasses expanding from the blown hatch hit the microphone; microphones register pressure changes generally, so if there is an expanding cloud of gas in space a microphone will pick up a "noise". I say "noise" because it's not truly acoustic sound because the medium is actually dispersing and the physical movement of that medium is what causes the "sound"; true sound is a wave phenomenon involving no gross transport of the medium.

[Ralathon]

Actually humans wouldn't overheat in space. We produce more heat than we can radiate away, but we're warmblooded animals and have ways to deal with this. Sweating would work perfectly fine in a vacuum, better even. That's how they keep astronauts on EVA's cool as well (venting steam). And since sweating is naturally tied to our body temperature anyway we'd be fine. The only issue is the extremities, these tend to radiate heat faster than blood can supply it. So your hands and toes would become pretty damn cold.

That said, don't step into vacuums wearing only a helmet. It isn't safe and likely very uncomfortable. There's a reason why they put astronauts in spacesuits instead of scuba gear.

[Sirrobert]

I like the idea of explosive farts if you ever get in a vaccum without pressure suit.

I hadn't concidered the problem with exhaling, but it makes sense. Don't jet fighter pilots also have some problems with breathing due to extreme G forces though? Or is that exactly the opposite?

[Camacha]

Would it not be a rather big problem that fluids tend to boil at room or body temperature in (near) zero pressure? I cannot imagine the moisture in all parts of your body (maybe the bit under a helmet excepted) being a pleasant or remotely healthy experience.

[Iskierka]

Your skin provides a small amount of mechanical counterpressure - fluids inside you won't boil, though exposed fluids like sweat and saliva will. And you don't get explosive farts in vacuum - closer to projectile diarrhoea, quite unpleasant.

Fighter pilot's breathing in extreme G forces isn't due to difficulties with it, and if it was it would be totally disconnected to low pressure - they use a special breathing technique, not to affect the air they get, but to intentionally put pressure on their gut through their diaphragm. This forces blood out of their lower torso, and combined with the flight suit that puts pressure on their legs to the same effect, blood is forced upward in the body and to the head, delaying blackout and maximising tolerable G-force.

Arguably it's similar, as vacuum causes blackout by forcing oxygen out of you, and thus the brain doesn't get enough, while high-G forces blood away from the brain and so oxygen isn't available, but the breathing technique is to prevent such from happening. And should not be attempted in vacuum - your throat is not capable of holding back 14 psi of air pressure trying to escape, and you'll just damage your lungs and throat trying to fight it. Let it out, do as much as you can with the ~14 seconds of consciousness available, and hope someone else can help you.

[jsisidore]

It would be pretty darn cold

Very informative (the quoted text that is). I always wondered how close to reality are those scenes in movies of people exposed to vacuum. The most recent ones I've seen were from the guardians of the galaxy and the gravity, albeit gravity's scene was you know what. Probably the most visual scene was from mission to mars, it was bashed by hardcore scifi fans, yet I love it.

I remember it to be a very sad scene.

[GreeningGalaxy]

Our good friend Project Rho, as usual, has enough to say on the matter to lay most of it to rest.

According to that, space might feel quite cold indeed at first, but after your skin water evaporated, you wouldn't feel much in the way of temperature unless unfiltered sunlight hit you, and then you'd certainly overheat quickly if you stayed in it for long (but probably not before the hypoxia got you).

Oxygen masks would be entirely useless, as you wouldn't be able to exhale without pressure surrounding your lungs - in fact, if you had any air in your lungs when you found yourself in the vacuum, they would probably burst.

Survival in a vacuum for very brief periods could be done, but I wouldn't make a habit of it.

[Scotius]

https://en.wikipedia.org/wiki/Space_activity_suit

Another portion of thought-food Very cool idea, methinks - but personally i would seriously freak out having to go into hard vacuum in a helmet and a suit that is not even pressurised

[Camacha]

Your skin provides a small amount of mechanical counterpressure - fluids inside you won't boil, though exposed fluids like sweat and saliva will. And you don't get explosive farts in vacuum - closer to projectile diarrhoea, quite unpleasant.

For this exact reason NASA is developing suits that work with mechanical pressure, not air pressure. If skin would be able to prevent mishaps on its own, this would not be needed. I do not think the slight pressure a skin exerts is going to be anywhere near enough.

And should not be attempted in vacuum - your throat is not capable of holding back 14 psi of air pressure trying to escape, and you'll just damage your lungs and throat trying to fight it.

Divers have been known to damage or burst their lungs if they surface without exhaling. This is partly due to the increased amount of air in your lungs when using diving equipment, but also because of the massive difference. A sudden loss of pressure cannot be good news. It will either rip your lungs to shreds, or you will die from vacuum drowning, or a combination. Either is a terrible, agonizing prospect.

[AngelLestat]

Actually humans wouldn't overheat in space. We produce more heat than we can radiate away, but we're warmblooded animals and have ways to deal with this. Sweating would work perfectly fine in a vacuum, better even. That's how they keep astronauts on EVA's cool as well (venting steam). And since sweating is naturally tied to our body temperature anyway we'd be fine. The only issue is the extremities, these tend to radiate heat faster than blood can supply it. So your hands and toes would become pretty damn cold.

That said, don't step into vacuums wearing only a helmet. It isn't safe and likely very uncomfortable. There's a reason why they put astronauts in spacesuits instead of scuba gear.

I am agree in mostly all less: "We produce more heat than we can radiate away"

??

What does it means?

You mean here on earth? Or in space?

In space that is not true if we are in the night side.. Because we are radiating with a temperature difference close to 300 degress, meanwhile here on earth we radiate with few degrees of difference (we are receiving radiactive heat from all objects).

Of course that process is not instant, it takes several minutes.

[Kruleworld]

Your blood won't boil, either

It doesn't boil, it effervesces, like opening a bottle of soda. (high pressure to low pressure)

[Mr Tegu]

It would mostly depend on the distance from nearest star and whether or not there are any objects in the way. Close to a star half of you would be extremely hot (how hot? no-one really knows) the other half would become frozen solid, if you were far away from a star or in shade you would quickly (how quickly?) become totally frozen.

"For instance, NASA’s bulky white spacesuits that astronauts wear on spacewalks can have

a temperature difference of up to 275 degrees F from one side to the other. This can happen if an astronaut has one

side of the suit facing the sun with the other side facing deep space."

(http://www.nasa.gov/pdf/379068main_Temperature_of_Space.pdf)

- - - Updated - - -

Anyone mentioned radiation poisoning yet?

[GreeningGalaxy]

Anyone mentioned radiation poisoning yet?

Ionizing radiation (presumably in the form of charged particles, which can be blocked by spacecraft hulls (unlike gamma rays)) is almost the least of your worries. Sure, it'll shorten your life if you manage to make it back inside before you asphyxiate, but your main worries while you're out there will be lack of oxygen, all the little bits of your body having pressure issues, and thermal/ultraviolet radiation from the sun if you have the misfortune to be outside something's shadow when you fall out the airlock.

[Sirrobert]

Ionizing radiation (presumably in the form of charged particles, which can be blocked by spacecraft hulls (unlike gamma rays)) is almost the least of your worries. Sure, it'll shorten your life if you manage to make it back inside before you asphyxiate, but your main worries while you're out there will be lack of oxygen, all the little bits of your body having pressure issues, and thermal/ultraviolet radiation from the sun if you have the misfortune to be outside something's shadow when you fall out the airlock.

Isn't all background radiation in space Gamma rays though?

[Kryten]

Isn't all background radiation in space Gamma rays though?

All parts of the spectrum, plus quite a lot of particulate.

[-Velocity-]

Isn't all background radiation in space Gamma rays though?

No, a lot would be protons, with the Sun being an especially powerful (and variable) source of potentially dangerous proton radiation. I suppose there would be alpha particles too, but not as many as protons, I would guess. Then there would also be x-rays (by the astronomical definition of x-rays/gamma rays which does not consider what the source of the photon is). And also, there would be ultraviolet, though it doesn't take much to protect against ultraviolet. I suppose there would also be small amounts of antimatter- for example, we've spotted a big cloud of positrons being ejected from the galaxy's core- but I don't know how much of those would be present in our neighborhood. Probably not a WHOLE lot, but we do know that Earth's magnetic field traps a small amount of antimatter so maybe you could have locally "high" concentrations of it. However, I would think that the effect of antimatter would be roughly equate into an increased flux of gamma rays, because antimatter particles convert to gamma rays upon interacting with regular matter.

The good news is that there shouldn't be any direct neutron radiation, I think, because I believe that free neutrons have short lives, so you only get neutron radiation when something is locally producing it.

But there's also another problem, a BIG problem- secondary particle showers. Basically, an extremely energetic particle hits some part of your spacecraft and creates a shower of high energy particles (kinda like a relativistic shotgun blast), and these secondary particles can be of just about any kind.

- - - Updated - - -

And just to be complete, really, you could get just about any element as cosmic ray. I said protons and alpha particles because they're the most common elements in the universe (hydrogen and helium), but there ought to be iron nucleus cosmic rays, oxygen cosmic rays, etc... I suppose there are even plutonium cosmic rays. Plutonium has a short half-life (20000 ish years for the longest-lived), but when it gets accelerated to 99.999...% the speed of light, time dilation should allow it to survive a trip of many billions of light-years. Actually, one of the first proofs of time dilation was the observation that unstable particles have much longer lives if they are travelling very close to the speed of light.

Edited February 24, 2015 by |Velocity|

[Bill Phil]

The effective heat of space on a human varies depending on where it is.

But the enemy ist really the cold so much as it is the lack of pressure...

[AngelLestat]

hey everyone... the topic was about how fast you lost heat in space.. not what can kill you faster under your own assumptions.

it start from a basic that you have oxygen... so how fast the the body lose heat. that was the question..

[Bill Phil]

That answer requires data we don't have. Unless you want to make an assumption...

Like the surface area of skin. There's an average, but it depends on the person.

[YNM]

Human body is hotter already than the CMB - so the most likely result is that you'd be pretty much a blackbody, in the IR spectrum (so, you lost heat instead of gaining it)... Cosmic rays, while dangerous, depends on the nearest star you live in (and which galaxy you live in). For Sun's position, more harm should be from Sun's radiation itself. A simplification that human skin is like both side of a board 2 x 1 meter dimension and a temperature of a bit over 300 K shows that the total heat you generate is 700 W. Sun's radiation would give you 2*1360 W at Earth's distance. Not sure how much that'd harm you, receiving additional ~ 2700 W every time. For instace, that's more than the wattage of most household things...

[Superluminaut]

The temperature of space away from a heat source is 3 Kelvin. That is colder than any environment on earth.

Most of your heat loss will be through sweat and radiation from your body. Which I suspect is slower than heat loss in a blizzard, or a pool of ice.

So, space is freezing, but you would freeze to death slower.

[Beowolf]

https://en.wikipedia.org/wiki/Space_activity_suit

Another portion of thought-food Very cool idea, methinks - but personally i would seriously freak out having to go into hard vacuum in a helmet and a suit that is not even pressurised

Once I did a lot of research on those suits. Jerry Pournelle often used these elastic suits in his fiction, and I was determined to find out exactly why we weren't using this awesome idea. Well, they worked great...almost. NASA worked on them for several years, but eventually gave up and assigned the research to MIT, to see if they could solve the two remaining problems:

1) The suits take literally hours to get into. The astronaut's essentially wrapping seven layers of Ace bandages, applied with lots of tension, over every inch from the neck down. By the time a team finished getting one astronaut dressed, they'd be too exhausted to work.

2) The other problem was male crotches. Testicles don't like being individually wrapped really tightly, and if there was any gap left at all the testicle would painfully expand into it. They couldn't work out any sort of cup design that'd hold against the pressure difference and not be too painful to wear. In his novels, Pournelle thought women's breasts would be the problem, but they said it was just like a sports bra. Men got the bad end of the gender stick this time.

[Ralathon]

1) The suits take literally hours to get into. The astronaut's essentially wrapping seven layers of Ace bandages, applied with lots of tension, over every inch from the neck down. By the time a team finished getting one astronaut dressed, they'd be too exhausted to work.

I wonder if we couldn't get around this problem by using modern smart materials. Say you build something that expands when you apply a current. So you grab a spacesuit, hook it up to a power source to loosen it up, get in, and unplug it so it grips you tightly.

Worst case scenario they'd have to cut you out of the suit if it somehow fails to loosen. And its a lot faster.