Sorry, Khan: it isn’t cold in space

Khan Noonien Singh, in Star Trek II: The Wrath of Khan

Do you know the Klingon proverb, ‘Revenge is a dish best served cold’?

It is very cold in space.

–Khan Noonien Singh, Star Trek II: The Wrath of Khan

I’ve always imagined space was cold. Probably Star Trek’s fault. It’s dark, it’s cold, it’s a vacuum, there’s nothing there. But in reality, there’s a ton of variation in the temperature of space!

Outside the solar system, it’s theorized to be about 3 Kelvin — minus 270 Celsius. That’s barely any heat at all, because it’s so far from any sun. But in Earth orbit, it’s about 50 Fahrenheit — the temperature of a spring day. And in the “wall of fire” recently discovered around the solar system, the temperature is almost 90,000 F!

But none of this is as meaningful as we think. Temperature, after all, describes the motion of molecules. In space there aren’t that many molecules to be vibrating. So Voyager was able to pass through the 90,000-degree plasma without a problem — it’s so thin that there isn’t much energy to transfer to the probe.

Likewise, in a cold place, like the surface of Mars, the temperature may be below zero, but there aren’t enough molecules to carry heat away from your spacesuit. You’re more likely to overheat than get cold. In a vacuum, or near-vacuum, the only way to transfer heat is by radiation. If you’re in the sun, the rays will quickly warm you up. In the shade, you’ll slowly lose heat as your body radiates it away. What you won’t do is reach an equilibrium with the “temperature of space” any time soon, since you brush a molecule so rarely.

Sometimes movies show people getting blown out an airlock and their skin immediately rimes with frost. That wouldn’t happen. If you were in the sunlight, you’d get a bad sunburn. But your corpse wouldn’t cool off until long after you were dead.

And you wouldn’t wear a sweater under your spacesuit, even on Pluto. Humans produce heat constantly, and we’re most comfortable in temperatures below 98.6, so that we can shed the extra. Without anything to cool you off, the inside of your suit would soon start to feel like a greenhouse, and then a sauna. That’s why spacesuits contain a whole cooling system–shedding heat at all times is vital to our health, and it’s not easy to do in a near-vacuum.

So, with all respect to Khan, he should maybe try getting his revenge in Detroit. In its ability to steal your body heat, it’s a lot colder than space.