The Moon isn't quite the wasteland we might assume it to be. Sure it's no oasis, but there's more water up there than scientists previously thought, and it was probably a far wetter and more active place in the distant past. Now, a NASA study has found evidence that the ancient Moon may once have had a watery atmosphere.

Some of the largest features of the Moon's pockmarked face are areas like the Imbrium basin, which formed billions of years ago from a collision with an asteroid that, at up to 300 km (186 mi) wide, was so large it could be considered a protoplanet. But what makes this region visible from Earth is the dark basalt rock that fills the basin, which flowed as lava some 3.5 billion years ago. Astronauts on the Apollo 15 and 17 missions collected samples from the edges of those ancient lava oceans (called maria), and later analysis revealed that gases like carbon monoxide, hydrogen, oxygen and sulfur, among others, would have been released at the time.

The new NASA study calculated just how much of those gases this volcanic activity would have created. The eruptions, they found, were intense enough that gases would have been spewed out of the surface faster than they could escape into space, forming a temporary atmosphere relatively rich in water vapor, that ensconced the Moon for about 70 million years. Eventually though, as the volcanic activity slowed the gases would have drifted into space, leaving our satellite the rocky husk we see today.

"The total amount of H2O released during the emplacement of the mare basalts is nearly twice the volume of water in Lake Tahoe," says Debra Needham, co-author of the study. "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."

These volatile gases, trapped in dark icy deposits at the Moon's poles, could be precious resources for potential missions in the future. Harvesting and processing them as sources of air and fuel could help astronauts set up more permanent operations, and in the far-distant future, these bases could be set up as refueling stations for manned missions to Mars and beyond.

The research was published in the journal Earth and Planetary Science Letters.

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