Does water freeze or boil in space? (Synopsis)

“You can’t cross the sea merely by standing and staring at the water.” -Rabindranath Tagore

And you can't answer a hypothetical question for certain, at least in science, without doing the experiment for yourself. Here on Earth, liquid water is plentiful; our planet has the stable temperatures and pressures that water needs to exist in its liquid state.

Image credit: NASA Goddard Space Flight Center Image by Reto Stöckli, Terra Satellite / MODIS instrument. Image credit: NASA Goddard Space Flight Center Image by Reto Stöckli, Terra Satellite / MODIS instrument.

But what happens if you take that water to space? In the vacuum of space, the temperatures are much too low for liquid water; everything should freeze. But the pressures are much to low for liquid water as well; everything should boil!

Image credit: Wikimedia commons user Cmglee. Image credit: Wikimedia commons user Cmglee.

So which one does it actually do? Don't just find out, come find out why!


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Ethan, slightly off topic, but topical nontheless in the light of the measured deuterium:hydrogen ratio in cometary water. As a comet has spent billions of years applying alternate cooking and cooling cycles to its surface layers, would this not tend to selectively evaporate the lighter H20 molecules, resulting in an apparent excess of HD0, at least in the surface layers sampled by Philae?

Why would water freeze quickly in space? I thought a vacuum was a good insulator, as in Thermos bottles. It seems to me a warm liquid introduced to outer space will slowly cool as it radiates heat, just as coffee slowly cools in a Thermos bottle. Where am I going wrong?

@Agnes #2: It's the surface-to-volume ratio. If you're picturing a big blob of water (like a pot-full), then you're right, and that's what Ethan described: The pressure drop affects the whole volume, so the water starts to boil (its own heat is above the boiling point at zero pressure) everywhere at once. That boiling essentially "explodes" the big blob into a huge number of tiny droplets.

Those tiny droplets are almost all surface, so they radiate away their heat (not conduct, but radiate in the infrared) and freeze/crystallize as "snowflakes."

Hence Ethan's answer: water in space boils _and_ freezes.

By Michael Kelsey (not verified) on 11 Dec 2014 #permalink

@Michael Kelsey: Thank you Michael. I see what you mean. So, an unprotected person would not quickly freeze in space because internal body pressure is maintained, thus keeping the surface-to-volume ratio fairly constant.


Why would water freeze quickly in space? I thought a vacuum was a good insulator

Just to add to what Michael said...
1. the liquid water state requires an ambient kinetic energy to maintain. Without an energy 'bath,' all those little H2O molecules will start radiating away their kinetic energy or redistributing it into other modes and start forming intermolecular bonds. As the vacuum of space has very little ambient kinetic energy, this happens quite quickly.
2. The wall-vacuum-wall configuration of a thermos works because it reduces heat exchange between the inside and outside of the thermos, not because the vacuum itself has the property of not allowing water to freeze. If you took away the inner wall of a thermos and exposed your liquid to the vacuum between the walls, two things would happen. First, your liquid would expand and cool. Second, the single wall layer remaining would not do a very good jod of insulating, and your hot chocolate or iced margarita would soon become the same temperature as the outdoors.


That's right. A person exposed to vacuum would not quickly freeze. The lack of external pressure, combined with an internal pressure, though, could well be disastrous. The body has evolved with the ability to withstand a fairly significant pressure differential where the external pressure is greater. (Think of scuba divers, for instance). I don't know enough about human physiology to know for sure, but I would suspect that a pressure differential of 1 atmosphere with the internal pressure being greater might get a bit messy.

Well, the worst bit is the sinuses. If you're ever evacuated into space, you should breathe out sharply, ESPECIALLY evacuating the nose. It can give you a good minute of extra life.

"evacuating the nose"

I have a feeling that if I were about to be shunted unprotected into space my sinuses would be the second or third thing I'd evacuate.

Breathing out sharply will leave a vacuum in your lungs, allowing oxygen in the blood to escape through the capillary walls. The quick loss of oxygen in the blood will lead to unconsciousness in 10-20 seconds.

By Michael Richmond (not verified) on 13 Dec 2014 #permalink

useful information....nice post....

By sigmatest (not verified) on 28 Dec 2014 #permalink