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Old 28th February 2010, 11:41 PM   #1
Third Eye Open
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question about mars

The atmospheric pressure of mars is much lower than that of earth.
Is it so much lower that it would instantly kill a human outside without a space suit, such as the famous scene from the movie 'Total Recall'?

Would it be possible to stand on mars with nothing but an oxygen tank and mask? To dig in the dirt with my bare hands?
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Old 28th February 2010, 11:57 PM   #2
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Surface conditions on Mars would be fatal for a variety of reasons.

You wouldn't be able to hold an oxygen mask on your face with the nearly 15 PSI differential. Surviving there without a suit would be like surviving in a balloon lofted to about 30 km altitude -- not feasible. If somehow you did, exposed skin would rapidly freeze.

Mars is susceptible to solar radiation storms, enough so that a sufficiently bad one would kill you without shielding.

What atmosphere Mars has is about 95% CO2. Any exposed water -- say your eyes, your open mouth -- would have a hard time deciding whether to freeze, evaporate, or absorb CO2 to produce carbonic acid.

Having said all this, Mars is closer by far to habitable conditions than any other known non-terrestrial environment. I hold out some hope that radical extremophiles could live there, and indeed may live there as we speak. As for you and I, though, not going to happen any time soon.
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Old 1st March 2010, 01:36 AM   #3
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Originally Posted by R.Mackey View Post
I hold out some hope that radical extremophiles could live there, and indeed may live there as we speak. As for you and I, though, not going to happen any time soon.
NEWSFLASH- "NASA scientist says Martians exist!!"
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Old 1st March 2010, 01:49 AM   #4
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I recently came upon some CT's claiming the martian "sky" is actually blue to blue-grey and not tinted red as most would think. The idea was that NASA color corrected the images to reflect a red sky, when in actuality it would be much different. Any truth to this or not?

And somewhat o/t --- would it be possible to station a long-term habitable ship orbiting Saturn and use Titan more or less for harvesting fuel to power the ship's resource needs?
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Old 1st March 2010, 02:26 AM   #5
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You might notice that on top of every lander we've dropped onto Mars is a color wheel in view of the cameras. That color wheel is used to correct the various filter coefficients so that they are properly represented in the final renderings.

When the first Viking lander landed on Mars in July of 1976 The first panorama it sent back had a nice blue sky shown. That was followed about a day later by a corrected print with the pink/orange sky we've grown to love, and apologies from the imaging team for the confusion. Ever since then the sky has been pink, the result of orange dust in the atmosphere. Presumably, then, the color of the sky would differ depending on the amount of dust present. It might actually be blue when viewed straight upwards.

Last edited by shadron; 1st March 2010 at 02:30 AM.
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Old 1st March 2010, 03:27 AM   #6
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Originally Posted by shadron View Post
You might notice that on top of every lander we've dropped onto Mars is a color wheel in view of the cameras. That color wheel is used to correct the various filter coefficients so that they are properly represented in the final renderings.

When the first Viking lander landed on Mars in July of 1976 The first panorama it sent back had a nice blue sky shown. That was followed about a day later by a corrected print with the pink/orange sky we've grown to love, and apologies from the imaging team for the confusion. Ever since then the sky has been pink, the result of orange dust in the atmosphere. Presumably, then, the color of the sky would differ depending on the amount of dust present. It might actually be blue when viewed straight upwards.
Yeah I started to read about the color wheel on the cameras, but then the article I was perrussing (sp?) started going into color theory and how we perceive color and so on and so forth and the drooling from my mouth commenced and I figured I didn't care that much afterall

But the overall thing was that originals with the blue sky were incorrect (i.e. the color wheel revealed the inconsistencies with how we perceive color on earth)? And so the Total Recall coloring was the real deal, given the amount of dust present at the lower levels in the atmosphere? Is this correct?

I thought Quade had finally melted the ice caps so we could all grow flowers there now, and that NASA was covering it up ...
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Old 1st March 2010, 04:02 AM   #7
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Originally Posted by trentwray View Post
But the overall thing was that originals with the blue sky were incorrect (i.e. the color wheel revealed the inconsistencies with how we perceive color on earth)? And so the Total Recall coloring was the real deal, given the amount of dust present at the lower levels in the atmosphere? Is this correct?
I don't think it was anything to do with inconsistencies in the way we perceive colours, it was just that the colour balance hadn't been calibrated. The first pictures were issued with an inaccurate colour balance which showed a familiar looking blue sky, but when the colour chart was photographed it became clear that there was really more red light and less blue. So the corrected images show what we would see if we were there; the sky is pinkish-grey.
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Old 1st March 2010, 01:02 PM   #8
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Originally Posted by trentwray View Post
I recently came upon some CT's claiming the martian "sky" is actually blue to blue-grey and not tinted red as most would think. The idea was that NASA color corrected the images to reflect a red sky, when in actuality it would be much different.
First, it is nonsense.

Second, ask the CT's what would be the purpose of this particular deception? I do not expect a convincing answer, but possibly an entertaining one.
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Old 1st March 2010, 01:11 PM   #9
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Originally Posted by Third Eye Open View Post
The atmospheric pressure of mars is much lower than that of earth.
Is it so much lower that it would instantly kill a human outside without a space suit, such as the famous scene from the movie 'Total Recall'?
I never saw the movie so can't tell, but people in vacuum do not explode, and do not die instantly. In vacuum a person would remain conscious for 10-15 seconds, and would die about a minute later (The famous scene in "2001: Space Odyssey" where Bowman enters airlock without a helmet is actually possible). Mars air is close enough to vacuum as to make no difference.
Quote:
Would it be possible to stand on mars with nothing but an oxygen tank and mask?
Not for long. Even if your mask were secured well enough to stand up to 15 psi pressure difference, you would suffer severe bends within minutes.
Quote:
To dig in the dirt with my bare hands?
Oddly enough, yes. Volunteers had spent as much as 30 minutes with both hands in a vacuum chamber, with no worse effects than some swelling. So if your space suit had airtight cuffs, then yes you could stick your hand into dirt on Mars. Or on the Moon.
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Old 1st March 2010, 01:18 PM   #10
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Originally Posted by Mark6 View Post
First, it is nonsense.

Second, ask the CT's what would be the purpose of this particular deception? I do not expect a convincing answer, but possibly an entertaining one.
If I remember it was:

* to keep "us" from understanding how habitable life on mars actually was
* they faked the martian rover expeditions on earth and accidentally leaked the photos showing this
* NASA is a conspiracy agency in general, yada yada yada
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Old 1st March 2010, 01:29 PM   #11
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Originally Posted by Third Eye Open View Post
The atmospheric pressure of mars is much lower than that of earth.
Is it so much lower that it would instantly kill a human outside without a space suit, such as the famous scene from the movie 'Total Recall'?

Would it be possible to stand on mars with nothing but an oxygen tank and mask? To dig in the dirt with my bare hands?
Bad things can happen to the human body if the ambient pressure drops too fast. In particular, you can develop decompression sickness, commonly referred to as "the bends". But the bends doesn't resemble that Total Recall scene. You aren't going to get anything even remotely resembling that. Note, though, that the problem is the rate of change in pressure. If given time to adapt, the human body can tolerate pressures well below 1 atmosphere. I'm not sure what would happen at Mars pressures, which are only about 1% of Earth's atmosphere. Even 100% oxygen at that pressure would provide you with only 5% of the oxygen than we normally get in each breath, so you might have trouble breathing just due to oxygen deprivation (though it's more complex than just oxygen levels since getting rid of CO2 is part of the equation, and that gets easier at low pressure). But the pressure differential won't pop your eyes out, even if you don't take any time to acclimate to the pressure differences. People have undergone bigger absolute pressure changes than that, and even in cases where decompression sickness is fatal, it doesn't look anything like Total Recall.

Which, BTW, was a stupid movie. If you want to keep it ambiguous whether or not the situation is real or only in his head, then you only show what he directly experiences. By including scenes where he isn't present, and in fact never even learns of, the movie confirms an external reality to events. Its attempts to go back to ambiguity at the end aren't interesting, they're a cheap gimmick that the movie itself has already discounted.
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Old 1st March 2010, 01:34 PM   #12
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Originally Posted by R.Mackey View Post
You wouldn't be able to hold an oxygen mask on your face with the nearly 15 PSI differential. Surviving there without a suit would be like surviving in a balloon lofted to about 30 km altitude -- not feasible. If somehow you did, exposed skin would rapidly freeze.
Yep. The thing that matters for respiration is oxygen partial pressure. On the Earth's surface, your body gets about 2.9 psi of oxygen mixed with nitrogen and whatnot. If you're climbing Everest with an oxygen mask, you can breathe yourself about 2.9 psi of oxygen almost all by itself---with only 1 psi or so of nitrogen diluting it---so in principle you can maintain sea-level-like respiration. Reinhold Messner, climbing Everest without a gas mask, is surviving---probably just barely---on 0.8 psi of oxygen (20% of a 300 mbar atmosphere). So perhaps we can call that a lower limit.

Mars' surface pressure is about 0.1 psi, so if you were holding an ambient pressure gas mask (like scuba gear) feeding you pure oxygen, you'd be a factor of 8 short of the Everest-without-gas lower limit.

Suppose you could crank the gas mask pressure up to 0.8psi and have it (lightly) strapped onto your face. There, now you're getting as much pure oxygen as Reinhold Messner. With this setup, without a pressure suit, your lungs are holding air at a somewhat higher pressure than the outside environment---this means they want to expand, and it's hard work to exhale. Every breath you take would feel like you're blowing bubbles through a hose whose end is 1.5 feet underwater. Try it! It's not going to make your lungs pop, but it's a good amount of work on every breath.

So the answer, I think, is MAYBE JUST BARELY. If you had Reinhold Messner's red-blood-cell-count, and you're able to do a good amount of work per breath, and you have an 0.8 psi overpressure oxygen mask---yes, you'll be able to breathe on Mars without a pressure suit.

I bet that a very low-grade pressure suit----a handful of rubber straps around the chest, at the level that'd make it difficult to inhale on Earth---would take a lot of the load off of breathing. Maybe you could get up to 1.0 or 1.2 psi.

Last edited by ben m; 1st March 2010 at 01:36 PM.
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Old 1st March 2010, 01:47 PM   #13
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Originally Posted by Mark6 View Post
Oddly enough, yes. Volunteers had spent as much as 30 minutes with both hands in a vacuum chamber, with no worse effects than some swelling. So if your space suit had airtight cuffs, then yes you could stick your hand into dirt on Mars. Or on the Moon.
Maybe, but that dirt is unlikely to be a comfortable temperature.
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Old 1st March 2010, 01:54 PM   #14
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Originally Posted by shadron View Post
When the first Viking lander landed on Mars in July of 1976 The first panorama it sent back had a nice blue sky shown. That was followed about a day later by a corrected print with the pink/orange sky we've grown to love, and apologies from the imaging team for the confusion.
And thats where the conspiracy comes from. The actual issues with the colour are more complicated:

http://en.wikipedia.org/wiki/Extrate...he_Martian_sky
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Old 1st March 2010, 02:01 PM   #15
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Originally Posted by Mark6 View Post
So if your space suit had airtight cuffs, then yes you could stick your hand into dirt on Mars. Or on the Moon.

Originally Posted by phunk View Post
Maybe, but that dirt is unlikely to be a comfortable temperature.
Or comfortable period. Lunar dust is so abrasive that it partially wore through the Apollo astronauts' gloves

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Old 1st March 2010, 03:10 PM   #16
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This is what MIT has been working on:



http://mvl.mit.edu/EVA/biosuit/index.html

I would expect that it would also need some sorted of electrical or water heating too. It seems pretty close to what Kim Stanley Robinson called 'walkers'.

Wish my professors had looked like that...
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Old 1st March 2010, 03:30 PM   #17
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Originally Posted by ben m View Post
<supporting data snipped>
So the answer, I think, is MAYBE JUST BARELY. If you had Reinhold Messner's red-blood-cell-count, and you're able to do a good amount of work per breath, and you have an 0.8 psi overpressure oxygen mask---yes, you'll be able to breathe on Mars without a pressure suit.
You know, I'd pondered things along those lines, but you actually had facts & numbers. That's one of the coolest things I've read in a while. Thanks!
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Old 1st March 2010, 03:48 PM   #18
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The instant recovery from the wild contortions and distortions on Ahnold upset me when seeing that.
Do that to anyone's face, and man, the pain and bruising and tearings of the muscles and skin would be awful, worth a few months in the hospital.
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Old 1st March 2010, 04:00 PM   #19
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Originally Posted by dasmiller View Post
You know, I'd pondered things along those lines, but you actually had facts & numbers. That's one of the coolest things I've read in a while. Thanks!
Seconded. It makes it seem like an intriguing possibility instead of movie fantasy.

I had just been thinking, by the way, that the transition would not necessarily be from 15 psi to near-vacuum. Whatever vessel brought you to Mars may well be built to contain a low pressure, oxygen rich atmosphere. I don't know what pressure of atmosphere spacecraft generally contain, but I'm sure I remember reading of space suits operating at about 5 psi.
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Old 1st March 2010, 06:01 PM   #20
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Originally Posted by I Ratant View Post
The instant recovery from the wild contortions and distortions on Ahnold upset me when seeing that.
Do that to anyone's face, and man, the pain and bruising and tearings of the muscles and skin would be awful, worth a few months in the hospital.
It's worse than that. Water isn't very compressible OR expandable, which means any noticeable volume changes due to pressure dropping would have to be in the form of gas bubble formation inside the body. That will tear more than just muscle and skin, that will tear blood vessels. All over the place. You'd be hemorrhaging like mad internally (including in the brain) to get that sort of effect. You wouldn't just be in a hospital for a few months, you'd be dead in a few seconds. Of course, to get that much bubble formation, you'd have to acclimatize a body to pressures FAR higher than 1 atmosphere before dropping them to near-vacuum. You'd essentially have to "carbonate" them (though not with carbon dioxide, since that would be fatal in its own right).
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Old 1st March 2010, 06:31 PM   #21
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Originally Posted by Third Eye Open View Post
The atmospheric pressure of mars is much lower than that of earth.
Is it so much lower that it would instantly kill a human outside without a space suit, such as the famous scene from the movie 'Total Recall'?

Would it be possible to stand on mars with nothing but an oxygen tank and mask? To dig in the dirt with my bare hands?
Too cold. Even in the Sun the surface temperature can be warm but only about an inch off the ground. A foot or more from the warmed surface and you start to see temperatures hundreds of degrees below freezing.


I haven't read the other replies yet so forgive me from being redundant.
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Old 1st March 2010, 07:14 PM   #22
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Originally Posted by Mark6 View Post
Oddly enough, yes. Volunteers had spent as much as 30 minutes with both hands in a vacuum chamber, with no worse effects than some swelling. So if your space suit had airtight cuffs, then yes you could stick your hand into dirt on Mars. Or on the Moon.
Somehow this makes me unreasonably happy.

Originally Posted by phunk View Post
Maybe, but that dirt is unlikely to be a comfortable temperature.
Originally Posted by Skeptic Ginger View Post
Too cold. Even in the Sun the surface temperature can be warm but only about an inch off the ground. A foot or more from the warmed surface and you start to see temperatures hundreds of degrees below freezing.
Wikipedia says that martian summers can have highs of 68F, is this incorrect, or am I misunderstanding it?

Thanks for the replies all!
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Old 1st March 2010, 08:07 PM   #23
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Originally Posted by ben m View Post
Yep. The thing that matters for respiration is oxygen partial pressure. On the Earth's surface, your body gets about 2.9 psi of oxygen mixed with nitrogen and whatnot...

I bet that a very low-grade pressure suit----a handful of rubber straps around the chest, at the level that'd make it difficult to inhale on Earth---would take a lot of the load off of breathing. Maybe you could get up to 1.0 or 1.2 psi.
Good post. A couple of additional details, though:

The effective suit pressure is a little bit higher because of two practical concerns. First is that there will also be a vapor pressure -- your own aspiration will displace some of the oxygen as you lose water into the super-dry tank air. Second is that there is some additional minimum operating pressure in your lungs.

So the actual minimum pressure for a 100% oxygen mix in a spacesuit works out to be a shade over 4 PSI, if we're delivering the same amount of oxygen as we're used to. If we're running at the ragged edge and don't mind blacking out, 3 PSI might be survivable.

Pure oxygen is rather dangerous and uncomfortable, however. Most spacesuits contain some inert gas in the mix, albeit not much since you have to carry it all with you. The A7L suits used in Apollo ran at about 5-6 PSI, running about 80% oxygen and 20% nitrogen. Yes, nitrogen -- unlike deep sea diving, there's no reason not to keep nitrogen in your system instead of flushing with helium. If you decompress, the bends will be the least of your worries...

Running at low pressure in a spacesuit helps in a few ways, one being it makes the suit less prone to bursting, another that it lightens the tanks. But some space applications are much closer to a "shirt-sleeve" environment. The International Space Station runs at full sea level pressure. This cuts down on the risk of fire, makes working more efficient, and provides some added protection from radiation.

It isn't clear what mix we'd use on Mars. I suspect it will be closer to the high pressure mix used on Station, but it's a complicated decision.
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Old 1st March 2010, 09:10 PM   #24
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I recall Spandex was promoted a long time back for a non-pressurized space suit capable of protection from internal problems for a short but useful period.
That fancy rip-stop suit seems to be a generation or two newer and probably more capable yet.
If anyone ever gets into real space, not LEOs, something like that may be the uniform, with the full-pressure suits for extended times outside in vacuum.
(Keep the oxygen mask close by. )
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Old 1st March 2010, 10:18 PM   #25
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Originally Posted by Third Eye Open View Post

Wikipedia says that martian summers can have highs of 68F, is this incorrect, or am I misunderstanding it?

Thanks for the replies all!
It's misleading. That is the surface temperature, but like I said, one only needs to get a few inches off the surface to see an incredible drop in temp.


Atmospheric temperatures are the featured Pathfinder meteorological observations
Quote:
The temperatures on the two Viking landers, measured at 1.5 meters above the surface, range from + 1 F, ( -17.2 C) to -178 F (-107 C). However, the temperature of the surface at the winter polar caps drop to -225 F, (-143 C) while the warmest soil occasionally reaches +81 F (27 C) as estimated from Viking Orbiter Infrared Thermal Mapper.
(emphasis mine)


But 1F at 1.5 meters up is much warmer than I had recalled. You could tolerate that temperature with a good coat. It would however, be during a very limited time window. And if you think about it, the warmest soil is 80F while the warmest air at 1.5 meters off the surface is 1F. That is an 80 temperature gradient from your toes to your waist. So what would the temperature be at 2 meters up then? It might be 40 below at your head even if it was 1F at your waist.

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Old 1st March 2010, 11:13 PM   #26
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Originally Posted by Mark6 View Post
Oddly enough, yes. Volunteers had spent as much as 30 minutes with both hands in a vacuum chamber, with no worse effects than some swelling. So if your space suit had airtight cuffs, then yes you could stick your hand into dirt on Mars. Or on the Moon.
I envisage a tiny frostbite problem...
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Old 1st March 2010, 11:25 PM   #27
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Originally Posted by Skeptic Ginger View Post
It's misleading. That is the surface temperature, but like I said, one only needs to get a few inches off the surface to see an incredible drop in temp.


Atmospheric temperatures are the featured Pathfinder meteorological observations(emphasis mine)


But 1F at 1.5 meters up is much warmer than I had recalled. You could tolerate that temperature with a good coat. It would however, be during a very limited time window. And if you think about it, the warmest soil is 80F while the warmest air at 1.5 meters off the surface is 1F. That is an 80 temperature gradient from your toes to your waist. So what would the temperature be at 2 meters up then? It might be 40 below at your head even if it was 1F at your waist.
Another point to remember is that while the air temperature may be very cold (or hot), it doesn't transfer much heat away from/to the body. Vacuum is just about the perfect insulator (for conducted and convected interchange), and atmospheric pressures below 1 atm are probably as good as Thermos gives you. It's even better than that in space. When the Skylab overheated, all that was needed was a thin mylar sheet to shadow the hull and the temperature inside dropped.
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Old 2nd March 2010, 04:42 PM   #28
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Originally Posted by shadron View Post
Another point to remember is that while the air temperature may be very cold (or hot), it doesn't transfer much heat away from/to the body. Vacuum is just about the perfect insulator (for conducted and convected interchange), and atmospheric pressures below 1 atm are probably as good as Thermos gives you. It's even better than that in space. When the Skylab overheated, all that was needed was a thin mylar sheet to shadow the hull and the temperature inside dropped.
OK, now that's an interesting concept. So would a human outside a space suit lose heat to that frozen vacuum? They may have to re-write a few sci fi scripts.
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Old 2nd March 2010, 05:04 PM   #29
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Originally Posted by Skeptic Ginger View Post
OK, now that's an interesting concept. So would a human outside a space suit lose heat to that frozen vacuum? They may have to re-write a few sci fi scripts.
In a vacuum, you can still lose heat through radiation. The power radiated for a blackbody is P = a s T4, where a is the area, s is the Stefan-Boltzmann constant, and T is absolute temperature. So the surface area of an adult man is about 1.9 m[sup]2[sup]. Arbitrarily picking a surface temperature of about 17 C (290 K), this gives us an upper bound to radiated power of roughly 300 Watts. Typical body power output is around 100 Watts. So yes, you can freeze to death in deep space, but it won't be terribly quick (just imagine how long it would take three 100-Watt bulbs to thaw a turkey).
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Old 2nd March 2010, 06:42 PM   #30
Skeptic Ginger
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Originally Posted by Ziggurat View Post
In a vacuum, you can still lose heat through radiation. The power radiated for a blackbody is P = a s T4, where a is the area, s is the Stefan-Boltzmann constant, and T is absolute temperature. So the surface area of an adult man is about 1.9 m[sup]2[sup]. Arbitrarily picking a surface temperature of about 17 C (290 K), this gives us an upper bound to radiated power of roughly 300 Watts. Typical body power output is around 100 Watts. So yes, you can freeze to death in deep space, but it won't be terribly quick (just imagine how long it would take three 100-Watt bulbs to thaw a turkey).
But your body is also making heat. So does the calculation mean one loses more heat than one's metabolism creates?

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Old 2nd March 2010, 10:16 PM   #31
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Originally Posted by Ziggurat View Post
In a vacuum, you can still lose heat through radiation. The power radiated for a blackbody is P = a s T4, where a is the area, s is the Stefan-Boltzmann constant, and T is absolute temperature. So the surface area of an adult man is about 1.9 m[sup]2[sup]. Arbitrarily picking a surface temperature of about 17 C (290 K), this gives us an upper bound to radiated power of roughly 300 Watts. Typical body power output is around 100 Watts. So yes, you can freeze to death in deep space, but it won't be terribly quick (just imagine how long it would take three 100-Watt bulbs to thaw a turkey).
If the person in question isn't actually naked, then there's insulation from the clothing, hair, etc. I'm not energetic enough to do the math (and my thermal analysis courses were among my least favorite) but I suspect that even relatively light clothing would be quite sufficient.

You specifically said "deep space," and I'm interpreting that to mean very far from any stars. But if someone was floating around in space in our neighborhood (1 AU from the sun), exposed to sunlight, then hyperthermia is a real possibility.

Of course, there are still the suffocation and lethal-radiation issues to deal with.
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Old 2nd March 2010, 10:26 PM   #32
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Originally Posted by Mark6 View Post
... Oddly enough, yes. Volunteers had spent as much as 30 minutes with both hands in a vacuum chamber, with no worse effects than some swelling. So if your space suit had airtight cuffs, then yes you could stick your hand into dirt on Mars. Or on the Moon.
Might get painful after a while;

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Old 2nd March 2010, 11:21 PM   #33
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Actually, much of the discussion of vacuum/heat conduction is incorrect. Vacuum is indeed a good insulator, but 0.1 psi is too high a pressure to "count" as vacuum. In fact, the thermal conductivity of air at 0.1 psi is almost identical to that at 1 atmosphere. (In a nutshell: as you lower the pressure, there are fewer molecules around to carry energy, but each molecule moves farther between collisions. The two effects cancel out.)

That goes both for conduction from one surface to another, as well as conduction to the air itself (I think). So yeah, Mars will freeze you by conduction---and do it quickly.

Convection is a bit harder to think about---I think most of the the relevant dimensionless numbers (Prandlt number, Raleigh number) have the same density/diffusion cancellation as the conductivity does, but they also have a gravity term---Mar's lower surface gravity might give you a bit of "insulation" by lowering the convection rate. (As you warm up the air around you, buoyancy won't carry it away as quickly in low gravity.)
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Old 3rd March 2010, 12:06 AM   #34
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The Rayleigh number is a little bit lower due to the lower gravity, but otherwise it's relatively unaffected by lower pressure. So convection on Mars is still quite significant. Even without this, however, there would still be convection -- actually advection -- because there's quite a lot of wind. The thin atmosphere also sets up very large scale convection patterns rapidly in daylight, large enough to be seen in terrestrial telescopes.

It's not as cold as the Lunar night, but you will be very unhappy without thermal control.
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