It’s not a real atmosphere like Earth’s, but a layer of sparse gases like helium, neon, and hydrogen. It’s so thin that atoms rarely collide. Solar radiation and micrometeorite impacts constantly replenish it. This exosphere affects surface chemistry and dust movement. Scientists study it to understand airless bodies. Lunar night and day cycles influence density and composition. It’s effectively a vacuum with trace elements floating around.
It matters for future lunar bases, as even tiny gas presence can influence experiments. Monitoring it helps spacecraft design.
It also offers clues about other airless bodies. Mercury and some asteroids have similar exospheres.
Some atoms in the exosphere can travel kilometers before colliding.
NASA [nasa.gov]