In my science class we were discussing how pressure affects the temperature at which water boils. For example at sea level water boils at 100 degrees Celsius. At a higher elevation it boils at a lower temperature because there is less pressure on the water. So I asked the professor at what temperature does water boil in outer space? She did not have an answer. So is it even possible to boil water in space and if so at what temperature does it boil at?

Yukos:

Let's assume the pressure in space is zero. If that is the case (and I believe it's pretty close to zero, if not zero) then the boiling point doesn't exist, because liquid water can't exist.

Take a look at a phase diagram, like this one:
http://wine1.sb.fsu.edu/chm1045/notes/Forces/Phase/Forces06.htm

At pressures below the "triple point" of water, liquid water can't exist. If you took a glass of water out of a space capsule, the water would almost instantly evaporate, or "boil."

As you can see from the phase diagram, the boiling points and sublimation points of substances change with changing pressure.

At very low pressures, below 4.58 torr, ice would behave the same way "dry ice" behaves -- when temperatures get high enough, it sublimates to become vapor without going through a liquid phase.

The normal boiling point of a fluid is that temperature at which its vapor pressure equals the ambient pressure. If you took flask of pure, degassed water - thermally insulated - and pulled a hard dynamic vacuum on it, it would cool by evaporation (absent nucleation) or frank boiling until it froze. The ice would then sublimate, continuing its temperature and vapor pressure reduction asymptotically. The rates would become negligible in terms of lost mass/second and degrees/second decrease at cryogenic temps.

Metastable supercooling; film and pore water. Pure particle-free water squeezed between two clean microscope slides has a melting/freezing point near -40 C.

OK Uncle Al!

Now could you put that in terms that not just a kid in science class, but even a soil scientist could understand? I was just going by my dim recollections of undergrad P. Chem.