The Moon Once Had An Atmosphere

In Moons by Brian Koberlein

For centuries humans have dreamed of traveling to the Moon. We achieved that dream in 1969, but found our sister world to be a dry airless rock. Most of the early stories of a journey to the Moon painted a very different picture, giving the Moon a breathable atmosphere, and perhaps even exotic life. We now know the Moon is barren of life, but there was a time when the Moon had an atmosphere. 

Our Moon doesn’t have an atmosphere because it is too small and doesn’t have a strong magnetic field. Any atmosphere it might have had would be stripped away by the solar wind that barrages the small world. In contrast, our planet has more mass to hold its atmosphere close, and a strong magnetic field to protect it. But that doesn’t mean the Moon couldn’t have had an atmosphere for a short time, and new evidence shows that it did.

About 3.5 billion years ago, the broad dark patches we see on the lunar surface first formed. Known as maria, they were created by large lava flows that later cooled to become basalt plains. During the Apollo missions of the 1960s and 1970s, astronauts brought back samples of these maria, and we found they contained traces of gas, such as carbon monoxide. This gas erupted from the Moon’s interior at the same time as the maria formed.

Recently a team calculated just how much gas would have been released from this process, and found it was more than originally suspected. So much gas was released that it would have formed a thin atmosphere around the Moon. The atmosphere only lasted about 70 million years, which is brief for geologic scales, but it could have deposited ice and other molecules in the cold sunless regions of craters.

And that could be important for future astronauts. In order to build a permanent presence on the Moon, humans will need water and soil to sustain us. If water and other compounds can be found on the Moon, we won’t have to bring it from Earth.

So our Moon is barren and airless today, but we might be able to live there thanks to the brief period when the Moon had a sky.

Paper: Debra H.Needham and David A.Kring. Lunar volcanism produced a transient atmosphere around the ancient Moon. Earth and Planetary Science Letters, Volume 478 (2017)