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Comment by error54 | Hacker News Reader

What the article fails to mention is that space is cold. Really, really cold averaging -454.81 Fahrenheit[1] making concerns about oxygen or water pressure irrelevant. The article should have been called "Survival in Vacuum Unprotected Possible."

1 - http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980301b....

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I worked on vacuum systems. Space is not cold, nor hot, nor happy. It's sort of the wrong way of looking at it.

Vacuum isn't. It is a terrible conductor of heat. So bad, that after 15 minutes a very small battery powered pen camera started to red on the edges of the video: it was starting to heat up! The only way to cool off is via radiation, which takes quite a while. If you had a large array of very conductive, high surface area material, then you could get cold. But our skin isn't like that. Rather, it's wet and insulative. The membranes that are wet immediately suffer evaporative cooling, but once frozen will have to sublime to cool any more, which is slow. The skin is dead on the outside and has layers of insulation in the form of water and fat.

No, the research, testing, and industrial accident reports show that you die from oxygen deprivation. (And you can find vacuum labeled as an asphyxiate, since inhaling it is deadly...)

EDIT: I should note that the temperature of the vacuum really is very low. That's not disputable. But there just aren't enough atoms in a vacuum for it to feel cold. It's one of those times our intuition about units sort of sets us up for failure: temperature is an average kinetic energy of each particle, and normally there are enough particles to matter. In a vacuum there usually aren't. (I'm lying of course: high energy plasmas can definitely heat something up given a few hours.)

Space is for all practical purposes a vacuum, thus the only cooling effect would be by radiation, given that the body wouldn't be in contact with anything around it, as opposed to what happens on the ground where it is surrounded by air or water in the sea. In these conditions, the change in temperature takes a long time.

As stated in the linked article:

"If we put a thermometer in darkest space, with absolutely nothing around, it would first have to cool off. This might take a very very long time. Once it cooled off, it would read 2.7 Kelvin."

So, the vacuum really is the main concern. You'd be long dead before you start getting cold.

Indeed. A living human probably generates more heat from the normal bodily processes than can be radiated away in space. For this reason spacesuits are equipped with coolers, not (AFAIK) heaters.

Thanks guys! I didn't even think about there being nothing around to transfer heat away the body. I would have figured that the fact that water boils and then freezes in space would mean (humans being mostly water) that a person would expire rather quickly unprotected.

I came across a neat explanation of why we don't freeze immediately: our skin's pretty good at keeping the wet parts of us inside! When I had been curious about this a few years ago, this was the thing that convinced me of it. After all, in order for the water in us to freeze, the higher energy water molecules need to go somewhere, right? (Of course, it's possible very small gas bubbles will dissolve into your blood, and that will quickly expire a person, but as noted elsewhere in this thread the pressure drop from atmo to vacuum is less than that normally experienced by divers.)

Also, I have covered a vacuum flange with my hand. Heckuva hickie, but otherwise harmless. Smarts a bit with a dash of bruising, but the skin holds up remarkably well.

There's an awful scene in the film 'Mission to Mars' where Tim Robbins removes his helmet in space, and his head instantly freezes. No, no, no!

The statement "space is cold" doesn't make much sense, since space, being a vacuum, is lacking any _thing_ to have a temperature at all. What little matter does exist in the vacuum of space is not going to conduct any significant heat from your warm body. An ordinary "space blanket" would keep you quite warm. Until you suffocated, of course.

How does vacuum (the absence of matter) have a temperature?

Outer space isn't a perfect vacuum.

http://en.wikipedia.org/wiki/Vacuum#Outer_space

Even if there were no atoms, you must consider the electromagnetic field (or photons if you want to think that you have particles).

If you have a perfectly empty box (with total vacuum inside) and the walls have some temperature (for example 2.7K) then, after a while, inside the box will appear the electromagnetic field with the blackbody radiation of the walls temperature.

It's convenient to assign properties to the electromagnetic field, in this case the temperature. And the correct temperature of the electromagnetic field inside the box is the same as the temperature of the walls.

And the best thing is that the walls are not necessary! You can assign a temperature to the universe background radiation. If the distribution of frequencies of the electromagnetic field is equal to the blackbody radiation of a 2.7K blackbody, then you can think that the temperature of the electromagnetic field is also 2.7K.

More details: http://en.wikipedia.org/wiki/Photon_gas

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