Why is Space cold?
It is the fact that any matter will have certain temperature which is obtained from the molecular speed. If the molecules are faster in the matter then the material becomes warm. The definition of vacuum says that the absolute vacuum is nothing or void and will not have any temperature. If the space consists of vacuum then the space also do not have any temperature. In that case space is also not cold. But, it was found that absolute vacuum do not actually exist and the molecules keep moving around in the space.
Some of the latest theories say that the molecules that exist around in the space consist of more mass than the galaxies that are visible if combined together. This collection of molecules is called as dark matterÃ¢â‚¬. The density of the molecules in the space that exist in between the planets and celestial bodies was found to be very less. In the view of space technology, the interplanetary space acts as absolute vacuum. Though the atmosphere on the moon is present and the density of air molecules is greater than that of those in the free space, the environment in the space was treated practically as absolute vacuum. This indicates that the exact measurable contact between the gas or air molecules on the moon and any other molecules was not observed. Due to this reason, the exchange of heat does not take place between these molecules on moon with that of others. Similarly, even the vehicles that are moving in the space will not possess any measurable contact with the space molecules and hence do not exchange any heat with the molecules in the vacuum around.
The same holds good even in Mars where the temperature is 30 degrees Celsius over there which cannot be felt by us as we can have on the earth. The atmospheric pressure also is very less on Mars that it cannot be measured by the vacuum pump that we use on earth. But according to our astronauts, the environment on Mars is Vacuum though it is not absolute Vacuum. Hence, space is considered to have vacuum insulated for convection heat. Space can have exchange of heat from the electromagnetic radiation. Like all other objects in space, anything that do not receive heat or generate heat in it will become extremely cold. This temperature of the dark space or cosmic background radiation was assumed to be about 3 Kelvin. Any object still deeper in the space can have still lesser temperatures also. But, it can never reach 0 Kelvin as per the second law of thermodynamics. This is because 0 Kelvin means absence of temperature and matter does not exist in 0 Kelvin.