You did it. You annoyed your crewmates enough that they did the unthinkable: they shoved you into the airlock and kicked you out of the space station. No suit. No air. Nothing. Just you and the vacuum of space. If you want to survive this grisly scenario, you’re going to have to act quickly.
First, It’s Going To Be Colder Than You Can Imagine...
But you’re not going to have to worry about freezing to death. Yes, space is generally cold, around 3 Kelvin, due to a bath of radiation soaking the universe known as the cosmic microwave background. However, the human body is rather inefficient at getting rid of heat, especially in the vacuum of space. There are three ways to transfer heat from a warm body to its surroundings: convection, conduction, and radiation. Convection is the movement of a fluid, like warm air rising to higher altitudes. Conduction is the transfer of heat through physical contact, like when you accidentally touch a hot stove. Radiation is just that: emitting electromagnetic radiation.
💀 Zero Kelvin is a measure of the coldest possible temperature, absolute zero. This is the point at which even molecules don’t move. There are no parts of space, or anywhere in the universe, that can reach this temperature. At this point, achieving absolute zero is only theoretically possible.
Without any air or water to surround your body, there’s no way for convection or conduction to transport heat and cool you off. Instead there’s just radiation. A typical human body emits around 100 watts of infrared radiation (about the same amount of energy as an old-school incandescent light bulb). That’s not all that impressive, and it will take several hours to bring your internal body temperature below freezing.
But the coldness and the vacuum of space is going to affect you in other, faster ways. For starters, any oils or moisture on your skin will immediately evaporate in the vacuum, leaving a nasty frostbite behind in their departure. Even though you’ll be surrounded by vacuum, you won’t explode. Your skin is pretty good at keeping your insides on the inside of you, so your blood won’t boil and your eyes won’t bulge out. Instead, you’ll suffer a rare vacuum-induced malady known as ebullism (not to be confused with an embolism, which is a type of blood clot).
Ebullism occurs when the surface of your skin is exposed to vacuum (which it now unfortunately is). The lower pressure on the outside of your body causes the liquids just inside your skin to expand, causing you to swell up. Fortunately we don’t have a lot of experimental evidence that has explored the full effects of ebullism, but in some cases of accidental exposure to vacuum, people have experienced swelling of up to twice their normal size.
That’s not going to be pretty, but it is generally survivable as long as you return to a pressurized environment within a few minutes.
But you’re not going to get a few minutes.
Don’t Hold Your Breath
The moment the atmosphere escapes the airlock, you might be tempted to hold your breath to buy you more time, the same way you would when going underwater. That is an extremely bad idea. The problem is that your squishy bits (particularly your lips, throat, and upper respiratory system) are not designed to hold in a lungful of air against a vacuum. All that air in your lungs will come out, despite your best efforts, and if you try to hold it back it will escape in an especially violent and sudden way, causing irreversible damage on its way out.
Just let the air out; it’s gone.
Here’s the fundamental problem that will eventually lead to your demise. In space, there’s no air to breathe (that’s kind of the definition of a vacuum). But your brain doesn’t know that – at least, the parts of your brain that are not under your voluntary control. Your heart keeps pumping. Your circulatory system keeps running. But your lungs are empty.
Low-oxygen blood comes to your lungs, ready to pick up some fresh air and transport it throughout your body. And then that blood leaves … empty. Very quickly, the oxygen saturation of your blood throughout your body drops. Recognizing the lack of this crucial resource, your body immediately goes into emergency mode. To preserve its most vital functions and conserve oxygen as much as possible, your body shuts down the most oxygen-hungry part of itself, which is your conscious brain.
Depending on your own unique physiology, you have somewhere between six and twelve seconds before you lose consciousness and completely black out.
That’s all the time you have to stay in control and get yourself to safety. After that, you can still be rescued (by someone else) and revived to relative normalcy, once you take care of the damaging frostbite and the unknown side effects of ebullism.
But eventually, the lack of oxygen will take its toll. One by one, your major organs will shut down. After only a handful of minutes you will suffer complete organ failure, otherwise known in the medical community as death.
A Post-Mortem Space Odyssey
What comes next depends on your exact position in space. If you happen to be within roughly the orbit of the Earth, you won’t freeze at all. Even though at that orbit the sun is 93 million miles away, it releases such an intense amount of radiation that it will keep your body (now corpse) warm for centuries to come. It’s the same reason that water stays liquid on the surface of our planet; there’s more than enough heat to do the trick, and it will have the same effect on you—prevent you from completely freezing. That warmth comes at a cost, however, as the sun’s intense ultraviolet radiation, which you are now exposed to outside the safety of a planetary atmosphere or spaceship hull, will slowly burn your skin away.
If you happen to find yourself exposed to a vacuum well outside the orbit of the Earth, or tucked away in some permanent shadow, then you will eventually turn into a human popsicle. Slowly glowing with infrared radiation, your body temperature will eventually reach equilibrium with the bitterly cold bath you find yourself in.
With your corpse frozen solid, covered in ice crystals, you will drift aimlessly between the planets. Unless you happen to land in a particularly unlucky orbit, you will never encounter anything larger than a micrometeoroid for the next few billion years. Those micrometeoroids will do their damage, however, as you slowly accumulate microscopic pockmarks from countless collisions with them. Over an extremely long amount of time—which to be perfectly clear, you now have—those endless impacts will individually dissolve your corpse, sending the organic molecules that was once your body scattering into a wide, diffuse debris field.
High-energy radiation streaming from the sun will collide with some of those particles. The chance of an individual collision is extremely low, but once again we have billions of years to play with. The occasional chance encounter will send some of your organic molecules on a solar escape trajectory, meaning that they have enough energy to leave our system and begin a journey into interstellar space.
With luck, those molecules will be swept up in the formation of a new solar system, perhaps becoming recycled into the emergence of a new life form on some distant, alien world.
Paul M. Sutter is a science educator and a theoretical cosmologist at the Institute for Advanced Computational Science at Stony Brook University and the author of How to Die in Space: A Journey Through Dangerous Astrophysical Phenomena and Your Place in the Universe: Understanding Our Big, Messy Existence. Sutter is also the host of various science programs, and he’s on social media. Check out his Ask a Spaceman podcast and his YouTube page.
