The Moon’s Fragile Exosphere: A Gas Cloud Disturbed by Lander Plumes

The Moon hosts a real but incredibly thin exosphere—mostly helium, neon, and argon—about a quadrillionth as dense as Earth's sea-level air. The gas is continually replenished and lost via solar wind, micrometeoroids, and surface processes, and can be locally overwhelmed by a nearby lander's exhaust, making contamination a key challenge for future measurements. LADEE data first detected neon and showed the exosphere varies with local time, underscoring that there is no stable atmosphere, only a dynamic, surface-interacting gas population that records both solar and lunar history.