How fast would you lose heat on murcury

[mehs]

Okay this is a weird question and world building. So assuming you are on essentially mercury, how fast would you be losing heat during night? The Wikipedia and such says that mercury gets as low as -180 Celsius, but it only has 1 trillionth the atmosphere of earth so you wouldnt be losing heat from convection as you would normally on earth. So if you were taking precautions to keep from losing heat from contact with the ground (stilts or shoe insulation etc), how quickly would you be losing heat? Would it be equivalent to the speed of losing heat in a vacuum (about 700-900 watts lost per hour from thermal radiation) or would it go significantly faster from contact with the ground and the minuscule atmosphere?

[Jack_Simth]

One trillionth of Earth's atmosphere might as well be hard vacuum as far as a living human is concerned (as in, unprotected human survival time isn't going to vary by even 1%). Contact loss is going to depend on the contact, for obvious reasons. Every material has it's own transmission rate - copper conducts heat much faster than, say, wood - which in turn is proportional to the heat difference.

Edit: Oh yes: And thermal radiation wouldn't be quite the only source of heat loss for a human in a (near) vacuum, even without ground contact: Water is going to evaporate off a body, and carry heat away with it.

Really, though, lack of air will probably kill an unprotected person before anything else. Probably won't have time to worry about the cold... and if your lungs happen to be full of air, you're going to rupture. And if there happens to be air in your blood, you're liable to get a case of the bends...

[zergling.exe]

This question doesn't really seem to pertain to the d20 system in any way. Is there a particular rule reason you asked here rather than in say the Mad Science and Grumpy Technology forum (http://www.giantitp.com/forums/forumdisplay.php?62-Mad-Science-and-Grumpy-Technology)?

[magic9mushroom]

Really, though, lack of air will probably kill an unprotected person before anything else. Probably won't have time to worry about the cold... and if your lungs happen to be full of air, you're going to rupture. And if there happens to be air in your blood, you're liable to get a case of the bends...

Decompressing from 1 bar (100,000 Pascal, ~sea level pressure on Earth) to vacuum is a bit different than decompressing after a dive (decompressing from anywhere between 1.5 and 20 bar to 1 bar). The bends care only about the interval between pressures, not their ratio, and as such you'd only get a fairly-mild case of decompression sickness (as opposed to the instant death (https://en.wikipedia.org/wiki/Byford_Dolphin#Medical_findings) people suffer going from 9 bar to 1 bar).

If you hold your breath, and your clothing isn't sufficiently tight and strong, your chest will expand beyond normal limits, causing damage to the lungs and other parts. If you don't, your lungs should be fine (as the air is free to get out), but you'll black out a few seconds later and die within a couple of minutes due to lack of oxygen (your lungs will actually work in reverse, filtering oxygen out of your blood, since however much residual oxygen is still in blood when it reaches the lungs is still more than there is in vacuum).

Basically, to survive more than a couple of minutes in space, you need an air supply to your face (within a pressurised mask) and some form of compression on the rest of your body (either a pressurised suit, or simply skin-tight material).

Assuming you have that, your next problem is definitely temperature. If you were in sunlight, you'd be likely to overheat even near Earth, but in near-darkness like a Mercurial night losing heat's definitely a problem. If your suit didn't provide any insulation at all, you'd be radiating a good 700-1000 W (while generating about 100-300 from metabolism) and would probably die after 30 minutes or so (big margins of error here, I'm not an expert). On the other hand, if your clothing provided enough insulation that the outer surface of your suit was at -10 to -20 C (dressed for going outside in Canadian/Siberian winter or Antarctic summer) or so, you'd probably be able to keep warm once you started shivering and would survive until you ran out of energy (assuming you didn't have food).

[Uncle Pine]

According to Frostburn, anything below -50°F (about -45°C) is considered "unearthly cold":

Unprotected characters take 1d6 points of cold damage and 1d4 points of nonlethal damage per minute (no save). Partially protected characters take damage once per 10 minutes instead of once per minute.
For complete protection against the effects of unearthly cold, a character must have a level of protection of 4 or higher. Level 2 or 3 is considered partial protection, and level 1 is no protection at all.
However, for the sake of space travel/exploring uninhabitable planets, I'd suggest to refer to the Nailed to the Sky (http://www.d20srd.org/srd/epic/spells/nailedToTheSky.htm) epic spell, which can be summed up to 2d6 cold damage and 1d4 vacuum damage per round.