Why Does Water Boil In The Vacuum of Space?
(Today we answer one of your questions by a reader who used our new ‘Ask Zidbits!‘ feature.)
In science fiction shows and movies, when someone or something is exposed to the vacuum of space, they’re often shown to instantly freeze. The vacuum of space is often depicted as a cold, barren place without atmosphere that can instantly kill without protection. User Heron34 asked us if the science behind those depictions is correct or exaggerated.
The Vacuum Of Space
One common misconception people have is that space is freezing cold. In space, there is almost no medium for conduction or convection of heat to take place. An object or body in space loses or gains heat energy through radiation. This means someone or something wouldn’t freeze instantly if exposed. In fact, depending on your distance from a star and if you were in direct sunlight, you may actually heat up. This is because the radiation you are receiving from the star would be greater than the radiation you would be losing. Strictly speaking, space has no temperature.
Lack Of Atmospheric Pressure?
Other than the lack of a breathable atmosphere, the second most dangerous thing to humans exposed to the vacuum of space is lack of pressure. In a vacuum, there is no pressure. This is critical for most liquids to remain in a liquid state because with no pressure, the temperature at which they start to boil drops. Water boils when there is no pressure (and as morbid as it sounds, so does blood).
This means that in the vacuum of space, a cup of water would boil into a vapor before it can freeze. It would eventually freeze, but it would – desublimate – or vaporize into a gas first, then turn directly into a solid.
What About Extreme Pressures?
On the opposite end of the spectrum, extreme pressures can give rise to exotic liquids. That extreme pressure allows Jupiter to lay claim to the biggest ocean in our solar system. This is because deep within Jupiter, the pressure of its massive atmosphere is intense enough to turn hydrogen gas into a liquid.
As you descend into Jupiter’s atmosphere, the hydrogen gas becomes hotter and eventually becomes a steam. As you continue to travel further, that pressure causes the steam to get denser until its indistinguishable from a hot liquid. This results in Jupiter having an “ocean” hundreds of miles deep.
However, It doesn’t end there. Beyond Jupiter’s liquid hydrogen ocean lies something even more bizarre. Combined with the atmospheric pressure and the pressure of that liquid ocean, it compresses the hydrogen into something else. A very exotic and special type of hydrogen called ‘metallic liquid hydrogen’.
Metallic hydrogen forms at pressures greater than 3 million times that of the Earth. Because of that extreme pressure, that “metallic hydrogren” ocean is hotter than the surface of the sun and glows an eerie blue. The closest thing we have to it on earth is liquid steel, and just like steel, it is a great conductor of electricity. This is what gives Jupiter its massive magnetic field.
It Can Rain Iron?
With even more pressure, like that found in Brown dwarfs, it can rain iron. Brown dwarfs are gas giants like Jupiter, except up to 75 times more massive. They don’t have enough mass to begin nuclear fusion and become a star, but because of their mass and pressure, they are still very, very hot. Though despite being called “brown” dwarfs, these “failed stars” glow cherry red like a coal ember cooling down.
Brown dwarfs are so hot and pressures so intense, that the clouds on a brown dwarf aren’t made of water vapor like on Earth, but of iron vapor. Further into the interior of these objects, the pressure becomes sufficient enough where this iron vapor will condense and it will “rain” droplets of molten iron like it rains water here on Earth.
The universe is certainly a strange and exotic place.