How to

9 June 2016

How Cold is Space?

Just to be clear from the outset, the question, “How cold is space?” doesn’t really make much sense. This is because heat, in simple terms, is movement. As kinetic energy builds in an object, either by the conversion of other forms of energy or heat transfer from other particles, its temperature increases accordingly.


The problem with this in space, however, is the distinct lack of particles to carry said kinetic energy. It is, after all, a vacuum. This prevents heat transfer by both conduction and convection, meaning the only way for heat to transfer in the depths of space is radiation, and the only real way to measure the temperature of space is to measure the temperature of an object or entity found or placed there.

The other problem with answering this question is the sheer vastness of space. As such, there is no single concrete answer as the temperature will depend on a multitude of variables, such as nearby planets and stars. So, let’s break it up a little.

Around the International Space Station, for example, objects in the shade experience temperatures of approximately -100°C, while metal surfaces exposed to constant sunlight rise as high as 260°C. To combat this heavy temperature shift, astronauts’ suits have to incorporate internal systems for both heating and cooling.

As you travel a little further from home, say, to the surface of ousted ex-planet Pluto, the cold gets a little more extreme. Standing on the surface, you would be subjected to temperatures as low as -240°C. This is only 33°C above absolute zero, which clocks in at -273.15°C.

Given all that, you would be forgiven for thinking that the farthest, most remote reaches of space would sit at absolute zero, far from the warming radiation of star systems, or anything at all really. It seems, however, that this is not the case. This is due to a phenomenon known as cosmic microwave background radiation, a remnant from the big bang, which is present throughout the entire universe. This background radiation means that even seemingly empty regions of space can maintain a constant minimum temperature of -270.45°C, or 2.7 Kelvin.


The radiation levels are steadily decreasing, however, leading in turn to a gradual decrease in the temperature of deep space, but we’re talking about a time frame of billions of years.


Sam Bonson

Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.