Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: FunkyMcGalaxy on 28/04/2018 14:42:52
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Hi y'all!
Popular depictions of death by unprotected exposure to the vacuum of space are notoriously hit and miss, but my question is a tad more specific. I understand that due to the pressure differential between the inside of the human body and the vacuum of space, any bodily fluids near an orifice (yikes!) or the skin will evacuate or rather evaporate into the zero-pressure environment of space. For liquid to freeze, on the other hand, wouldn't it require *more* pressure rather than less?
I ask because the single most common trope of space death in sci-fi movies is the dramatic forming of ice crystals on the victim's eyeballs and lips. Would it not be more accurate to depict water vapour steaming from the eyes and any other soft membranes?
I suppose it also depends on whether you're directly exposed to sunlight or not?
Grateful for any answers! I'm not a scientist, so if I've gotten this completely wrong, please correct me. :-)
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The boiling of liquids in a vacuum causes heat to be drawn away from them, resulting in the remainder of the liquid decreasing in temperature:
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The eyeballs themselves wouldn't freeze but the tears on the surface of the eyes would rapidly evaporate and leave behind ice crystals.
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There have been experiments in space.
http://iopscience.iop.org/article/10.1143/JJAP.33.6648
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Exposed to zero pressure in space; what would stop the pressure of the aqueous humour from causing the eye to explode?
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Exposed to zero pressure in space; what would stop the pressure of the aqueous humour from causing the eye to explode?
The fact that the pressure is low and the eyeball is quite strong.
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@Kryptid Interesting video - thanks; I wouldn't have predicted that. I'd have expected the water to boil away until none remains. Thank you for educating me!
I think it's also worth mentioning that, without the attenuating effect of the Earth's atmosphere, solar radiation is extremely powerful in space, so exposed tissues would potentially see very high temperatures. I wonder what effect this would have on the outcome?
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I think it's also worth mentioning that, without the attenuating effect of the Earth's atmosphere, solar radiation is extremely powerful in space, so exposed tissues would potentially see very high temperatures. I wonder what effect this would have on the outcome?
The atmosphere absorbs a lot of the short wavelength stuff, but it actually transmits most of the radiation from the Sun.
If I remember rightly, the figures are that about 1350 watts fall on each square metre of the atmosphere and about 1000 of those are transmitted to the ground,
But it's also important to remember that the atmosphere is part of the Earth.
Much of the energy absorbed by the atmosphere goes into warming the Earth.
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The fact that the pressure is low and the eyeball is quite strong.
I'm trying to interpret that in a way that gives me information about the possibly explosive fate of the eyeball. Are you saying that the eyeball is strong enough to withstand internal pressure if exposed to a situation of zero pressure?
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The fact that the pressure is low and the eyeball is quite strong.
I'm trying to interpret that in a way that gives me information about the possibly explosive fate of the eyeball. Are you saying that the eyeball is strong enough to withstand internal pressure if exposed to a situation of zero pressure?
When trying to see whether a barrier will collapse "due to pressure," one must consider the pressure on both sides of said barrier. For instance, 20 atmospheres is a lot of pressure, but if both sides are under 20 atmospheres, there is no net pressure pushing the barrier one way or the other.
In the case of an eyeball in space, we can take the pressure of space to be 0 (it is ever so lightly greater than that, but it doesn't matter for this level of calculation), and we can take the pressure from the water to be the vapor pressure of water. At body temp (37 °C) the vapor pressure of pure water is 47.1 mmHg (0.062 atm, so not much), and the vapor pressure of the fluid in your eye will be lightly less (maybe 5% lower?) than that because it is not pure water (and the impurities are mostly proteins and salts, which are not volatile).
So if we assume a pressure of 45 mmHg, which is about 0.6 N/cm2, this wouldn't be comfortable, but I don't think it would burst your eye.
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Thanks Chiral. I think I'll try to avoid exposing my eyeballs to space, anyway.
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Exposed to zero pressure in space; what would stop the pressure of the aqueous humour from causing the eye to explode?
It wouldn't explode anyway. Something only explodes in that manner when he containing vessel ruptures and someting like a gas escapes. In this case the eye would only swell to its maximum. IO see no reason for it to exlode. A bag of water wouldn't explode. It'd just freeze like I asssume the eye would.
Blech!
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45 mmHg, which is about 0.6 N/cm2, this wouldn't be comfortable, but I don't think it would burst your eye.
This is looking at the pressure that the eye would sustain when exposed to a vacuum.
However, in normal life, eyeballs are exposed to a variety of insults like walking into a tree branch or a fistful of knuckles, and overall the eyeball survives pretty well, considering. It has a pretty tough outer membrane called the sclera.
See: https://en.wikipedia.org/wiki/Sclera
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What a nice video
And a phase change :)
Pretty cool
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This is too juicy to pass up !
An outward pressure of ~4 psi. would make your eyeballs go popeye , like Total Recall . They might also go " Bluurst ! " , like Ted Freakin' Bundy's !
Yiyiyiiiy !! Jara