Billions of years ago, the Moon would have looked really different. Lava would have flowed on its surface and, according to new research, our satellite would have also had an atmosphere.

The study, published in Earth and Planetary Science Letters, looks into the period when the Moon interior was volcanically active around 3.5 billion years ago. Molten rock from the interior would have erupted on the surface and flowed across it. The darker region that we can see, the maria, formed from this material.

But lava wasn’t the only thing escaping the interior of the Moon. Water, sulfur, and other volatiles were also freed during the volcanic eruptions and according to researchers Dr Debra Needham and Dr David Kring, these gasses ended up forming a transient atmosphere that lasted for about 70 million years.

“The total amount of H₂O released during the emplacement of the mare basalts is nearly twice the volume of water in Lake Tahoe," Dr Needham from the NASA Marshall Space Center, said in a statement. "Although much of this vapor would have been lost to space, a significant fraction may have made its way to the lunar poles. This means some of the lunar polar volatiles we see at the lunar poles may have originated inside the Moon.”

Water has been found on the Moon at the poles and in rocks across the surface. The regions at the poles are particularly interesting. They are in permanent shadow from the Sun so it is likely that hints of this primordial atmosphere may be hidden inside the frozen ice.

“This work dramatically changes our view of the Moon from an airless rocky body to one that used to be surrounded by an atmosphere more prevalent than that surrounding Mars today,” Dr Kring, a senior staff scientist at the Lunar and Planetary Institute, added.

The work was possible thanks to the lunar rocks collected by the Apollo 15 and Apollo 17 mission in 1971 and 1972, respectively. These samples hold the crystallized history of these eruptions allowing scientists to work out when they happened and what kind of gasses the lunar volcanism released.

This analysis is important for future crewed missions to the Moon and it will help us understand what kind of resources can be found on our satellite.