(NewsNation) — Scientists discovered the source of the moon’s atmosphere, a mystery that has puzzled researchers for decades.

The moon is generally thought of as having no atmosphere, which is true if you’re thinking of a robust atmosphere with breathable air like we have on Earth. The moon’s gravitational pull is too weak to trap the gasses needed to create such an atmosphere.

There is a weak layer of gases known as an exosphere on the moon, which was discovered during the Apollo program.

What has stymied scientists is how the moon maintained an exosphere as atoms were constantly swept away due to gravitational. Without a source to replenish it, the exosphere should have been stripped away by space weather long ago.

According to a new study, researchers now believe the exosphere is maintained by collisions of tiny micrometeorites with the moon’s surface.

Researchers said the collisions result in impact vaporization, releasing gasses that form the exosphere. They came to the conclusion by examining alkali metals, specifically potassium and rubidium, which are vaporized in the impacts.

In addition to answering a long-standing question about the moon, the research could give scientists clues on how to determine if similar processes are happening on asteroids or other planets’ moons.