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Astro Quiz 38: Color of Blood in Space?

Question #38 – If you got a cut in space, what color would your blood be?


There is a lot to unravel here as the physical reaction of liquids in space is counter-intuitive, but we will start with the color of your blood immediately after leaving your body in space. A common misconception is that our blood is actually blue in our veins and only turns red once it is exposed to oxygen in our atmosphere. In reality, our blood is always a shade of red (bright red when full of oxygen and maroon when oxygen deprived) and our veins only appear blue because our skin and fat cells absorb the low-energy red light from the Sun. This leaves only high-energy blue light to be reflected from our maroon veins. So, if you cut yourself in space, your blood would be a dark-red, maroon color.

But what happens to your blood once it leaves your body in space? Does it immediately freeze due to the temperatures hundreds of degrees colder than what we experience here on Earth, or does it immediately boil due to the lack of pressure in the vacuum of space? Surprisingly, the answer is both! First the warm water in the blood would vaporize due to the lack of pressure, then almost immediately would freeze once the vapor cools to a cold enough temperature. This would happen through the process of deposition, or the transfer from gas to solid skipping the liquid phase entirely!

So, if you were alive long enough to see it happen, you would see your maroon blood evaporate and expand into a gas cloud that almost immediately freezes into a network of minuscule ice crystals.

Read "If Blood Is Red, Why Are Veins Blue?" at and "Lost In Space Without a Spacesuit? Here's What Would Happen" at for more info.

This question was provided by Jordan Levy, age 14. Jordan lives in Jerusalem, Israel

Be careful not to cut yourself in space lest you attract space sharks
Image credit: Sharknado 3



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