[silvio]

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.

[gmaslov]

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.

[error54]

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.

[HCIdivision17]

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.

[danellis]

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!