We finally know where the moon's atmosphere comes from

It is easy to imagine the moon as an atmosphere-less hunk of rock orbiting Earth. However, while lacking breathable air, our planet's loyal natural satellite companion does have a thin and wispy atmosphere.

Scientists have long puzzled over the existence of this tenuous atmosphere or "exosphere" and have searched for the main process that sustains it, but new research indicates that this tenuous lunar atmosphere or "exosphere" owes its existence to renewal and replenishment caused by the violent bombardment of space rocks upon the moon.

The team behind the research suggests that the moon's atmosphere is mainly sustained, and has been for billions of years, by this assault causing a phenomenon called "impact vaporization." This process occurs when impacts kick up lunar soil, vaporizing materials that either escape to space or remain suspended over the moon, thus renewing its exosphere.

"We give a definitive answer that meteorite impact vaporization is the dominant process that creates the lunar atmosphere," team leader Nicole Nie, an assistant professor at the Massachusetts Institute of Technology (MIT), said in a statement. "The moon is close to 4.5 billion years old, and through that time, the surface has been continuously bombarded by meteorites. We show that eventually, a thin atmosphere reaches a steady state because it's being continuously replenished by small impacts all over the moon."

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The moon's history of violence

The moon's pitted and scarred surface is a clear and obvious geological reminder that it has been peppered with space rocks throughout its near 4.5 billion-year history.

Early in the moon's lifetime, the infant solar system was violent and turbulent. As a result, the lunar surface was frequently struck by massive meteorites. As time progressed, collisions between solar system bodies ground many larger space rocks down. This meant that as the moon aged, the bombardment continued, but the assailants shrank to smaller "micrometeoroids," particles from space that are smaller than a grain of sand. Yet, these less dramatic impacts were still sufficient to allow impact vaporization to continue and to continuously replenish the moon's atmosphere.