Why does Mercury have no atmosphere?
Mercury has a very thin atmosphere. It is so thin for several reasons. First, it is a low mas planet (greater than our moon’s, but less than Mar’s), therefor gasses in its atmosphere can more easily escape. Second, it’s very close to the sun, so its day side is very hot, the heated gasses of its atmosphere are more likely to escape into space. Third, its magnetic field is very weak, so the solar winds can more easily blow away its atmosphere. Finally, it’s night side is very cold, so any gasses that reach there are frozen and collect on the surface until the next Mercury day (about once every two Mercury years).
