Re: Is there air in space? What happens to air if released in space?

Unwanted air can and does accompany objects into space, and spacecraft have to be equipped in order to let trapped air escape. There are vents, for example, in the space shuttle's payload bay to allow this to occur. These vents also allow air back into the unpressurised cargo bay during the return from the near-vacuum of orbit to Earth.

Air at sea level comprises of a mix of small molecules (primarily N₂, O₂, Ar and CO₂) jostling about and colliding with each other. The average speed of their movement is some 450 metres per second, and due to the density of air at sea level (i.e. the number of particles in it) particles typically travel only around 100 nanometres between collisions. This distance is known as the mean free path. Now, the speed of the particles is directly linked to temperature, and the pressure of a gas stems from this speed and the density of the gas.

At typical space shuttle operational altitudes - around 350km for trips to the International Space Station - the pressure is approximately ten billion times lower than at sea level. At these extremely low pressures, the mean free path is several kilometres in length. It's intuitively obvious that any confined gas at surface pressure, if allowed access to such a near-vacuum, will lose molecules from its surface, as collisions will occur infrequently (that is, there's no pressure keeping them in place). The process of losing molecules (lowering density) will result in a loss of pressure.

As mentioned, the use of vents on spacecraft allow this loss of pressure to occur slowly during the trip to orbit (which typically takes 8 minutes or so) and not explosively - what would happen if, for example, a pressurised section was holed by space debris.

For more information on gases, I can do no better than refer you to the Hyperphysics website on the Kinetic Theory of Gases.

I hope this has answered your question.

Andy