> If you're inside a spacecraft, and you release water into outer space, what doesthe water do first?And the answer: boil.Photo credit: NASA.As air pressure decreases, the boiling point also decreases.So in a vacuum-like outer space, water boils. In fact, astronauts report thatwhen they release liquids from their spacecraft, the liquids rapidly boil. Soonafter, the vapor then freezes, producing very fine crystals.Inside an oxygenated, zero-gravity environment, water becomes spherical. Thismakes sense, as without gravity to tug downward, the forces governing theobjects are all the same. Consequently, the water droplet can only form theshape which has the least amount of surface area: a sphere. However, outside of a pressurized environment, water changes form rapidly.Interstellar space actually has a pressure that’s millions (or even billions) oftimes smaller than Earth's, and the temperature is very, very cold. Thus,because water boils at a lower temperature at high altitudes, a low enoughpressure will cause the water to immediately boil. When we talk about puttingliquid water in the vacuum of space, we’re talking about doing both thingssimultaneously: taking water from a temperature/pressure combination where it’sstably a liquid and moving it to a lower pressure, something that makes it wantto boil, and moving it to a lower temperature, something that makes it want tofreeze.Once the water has boiled, we then have isolated water molecules in a gaseousstate, but a very, very cold environment. These tiny water vapor droplets nowimmediately freeze (or, technically, desublimate), to become ice crystals.Learn more about the effects of space on water below.