Since the earth is in a vacuum and therefore there is no thermal transfer of heat to anything else, how can it even cool down? It seems like its average temperature would always be constant, ignoring outside sources of heat.
However, if you then consider that there is constant radiant heat transfer from the sun to the earth, now you have a net gain in energy/heat.
I also read somewhere that the solar wind actually blows a bit of our atmosphere into space, but that seems like a miniscule amount of heat loss compared to how much heat is gained from the sun.
Will the earth ever cool at all?