The temperature of outer space is 2.73 Kelvin (-270.42 Celsius, -454.75 Fahrenheit). This is actually the temperature of Cosmic Microwave Background Radiation, which is spread throughout the entire universe.
The unfathomable void of space seems like an incredible travel destination, even though it’s mostly filled with, well… nothing. However, if you did get a chance to visit space, what would you need to pack? The coldest city on earth is Yakutsk, Russia, averaging temperatures of about -50 C (-58 F) throughout the year. That may seem extreme, but space might get a bit colder than that, so don’t forget to pack the extra sweater that grandma made for you…
Of course, assuming that you don’t leave your spaceship without a spacesuit, you won’t have to worry about any of these freezing temperatures, as the spaceship’s temperature would be thermally controlled. Without thermal controls, things would start getting a bit crazy. The sun-facing side of the International Space Station, for example, can reach scalding hot temperatures of about 121 C (250 degrees F), while thermometers on the dark side can plunge to a biting -157 C (-250 degrees F). Thank god for air-conditioning, right? However, before we answer the question, there’s something you should know…
Space Has No Temperature
Temperature is basically the bulk measure of the hotness or coldness of a body. Heat, on the other hand, is the total kinetic energy of the molecules inside the body. Essentially, temperature is the average heat of a body. However, in the vacuum of space, you can get densities of matter as low as 1 atom per cubic meter, in contrast to Earth’s atmosphere, which has 1021 atoms per cubic meter.
There are so few particles out there that measuring the temperature of a vacuum is almost meaningless. Still, we will plod on and try to determine what the temperature of outer space could be.
How Cold Can it Get in space?
The coldest possible temperature in the universe has the ominous, sci-fi sounding name of Absolute Zero. The value of Absolute Zero is –273.15 C (–459.67 F) or simply, 0 Kelvin. It’s physically impossible for a substance to reach this temperature, because at Absolute Zero, all kinetic energy in a molecule ceases to exist and no further heat can be extracted from it. Theoretically, it is impossible to reach this temperature, because at Absolute Zero, quantum mechanics starts rearing its ugly head, and due to some complicated interactions involving a certain Heisenberg principle, we’ve decided to leave it at that.
What’s the Temperature of Space?
Let’s say we bring out a very precise thermometer into space. There’s gas, dust and ionized particles from the Sun (known as “solar wind”) flying around, but these particles are so incredibly far apart that very few of them, if any, would bump into your thermometer. Even if they do, they’ll be pretty cold, and the vacuum between them, void of any baryonic matter, wouldn’t be detected. Slowly, your thermometer would start radiating its heat away. Its recorded temperature would continue decreasing until it reached a temperature of 2.73 K (-270.42 C, -454.75 F), the temperature of Cosmic Microwave Background Radiation.
Cosmic Microwave Background Radiation is a remnant of the most powerful explosion in history: the Big Bang. The photons from the event that gave birth to time and space still permeate the cosmos today, causing slight radio interference and heating up space thermometers for curious scientists like us. It’s possible to reach colder temperatures than that in labs on Earth, but out in space, the constant buzz of this omnipresent emission creates a sort of universal average temperature. To conclude, we can say that the average temperature of space is 2.73 K. So… thanks, Big Bang, for continuing to warm our hearts (and thermometers) 13.8 billion years later.