What would happen to say a litre of water in space?

Assuming one could arrange it, would it slowly boil, freeze, instantly vaporize, explode?
Could I convince NASA to try it?

It would boil almost instantly.

Ok, I’m not a science person obviously-- so the radiation or whatever out there is great enough to overcome that whole almost-0 Kelvin temperature? It’s NOT very cold in space? (thanks, Khan)

ETA: Actually… is this a lack of pressure issue?

I hope I’m not being whooshed.

It’s neither cold nor hot in space - vacuum isn’t capable of having an ambient temperature - things can cool and be heated by radiation only (actually, cooling by evaporation is also possible) A hot thing would stay hot for longer than it would in an ordinary room on Earth (for the same reason that hot coffee stays hot in a thermos - vacuum is a good insulator)

Barring some very odd circumstance, yes.

Presumably your water starts out at room temperature, and you suddenly expose it to vacuum. Under those circumstances, the radiation from the sun is irrelevent. The drop in pressure will be enough to cause instant boiling. That boiling will quickly cool the remaining liquid water, and it will freeze.
If your water’s in something like a plastic soda bottle, that freezing will take only a minute or two. Of course, if the water happens to be floating near the spout end of the container, steam pressure will force it out of the bottle, and you’ll have a rocket.
After the water has boiled, and frozen, radiation from the sun will have time to drive sublimation, and your chunk of ice will slowly disappear: freeze drying .

IIRC the boiling point of water in a vacuum is around 85 degrees farenheit. I don’t know the exact number but in fire academy we were warned about this from stories of pump damage people had experienced attempted to draw water for firefighting from swimming pools with water at like 90 degrees.

Would it truly boil away in that it becomes a gas, or would the air escape quickly as the water molecules for the most part never turn to a gas?


Uh, wha? Steam is the gas form of water. Granted its not a stable gas at standard atmospheric temperature and pressure and condenses quickly, but it is a gas.

Nope, here’s the phase diagram. Water in vacuum boils at about 200°K, that’s -73°F.

At 27" of vacuum the boiling point of water is 75F

I stand corrected, I had not hunted for the specifics, I just knew at lower pressures like you might find drafting water from a pool it does boil at dramatically lower temps. Ignorance fought.

<nitpick> That’s -73 °C, which is -99.7 °F.

Yup, score one for the Venusian pie plant!

Like I sad does water become a gas or is the disolved air just rapidly leaving the water? Would the water appear to boil if no dissolved gas was in it?

I posted about an hour ago but my post seems to have boiled off into space. Damnit! Worse, I cant find the references again, god knows what I used for a search term and looking in the history is no good 'cause I’ve rebooted and the history and everything else clears on reboot.

I have a vague recolection that NASA once said that urine ejected from orbital vehicles was causing a problem by clogging the vents as it froze on exposure to ‘space’. At low enough temperatures and pressures water can boil and freeze at the same point.

A couple of articles that don’t answer the question precisely but make me think that it would boil/evaporate/disperse in the vacuum rapidly untill it had lost sufficient energy to remain liquid upon which it would freeze and sublimate very slowly until some energy input allowed it to resume a liquid state and continue to evaporate.


I appear to have lost the other one but it was that you filled a closed glass tube with mercury and inverted it in a trough of mercury. the mercury in the tube would drop consistent with the air pressure on the surface of the mercury in the trough creating a vacuum, or at least an area of severely reduced pressure, in the top of the tube. Using an eye-dropper you introduced water into the bottom of the tube and injected a drop into the bottom of the tube. As it is less dense than the mercury it would rise to the surface then explode into vapour in the cavity at the top of the tube.

I believe NASA solved the problem by putting some spin on the vehicles, not sure about the ISS though. Maybe they have a plumber there who EVA’s and chips it off with a hammer?

A related item is that comets are composed of a combination of water ice and bits of rock and metal debris. They remain substantially intact until they approach a star closely enough to have the ice turn into vapour - th comet’s tail. So it seems to me that ice would be stable enough until some energy were applied to it in the form of sunlight.

Yes. The water actually and truly boils.

Thanks that’s what I wanted to know