The Moon has more water than previously thought, and it’s deep below the lunar surface. A new study suggests that water is widespread beyond the poles, where it was already known to exist, although scientists don’t know exactly how much water is there. The discovery has consequences for future missions to the Moon.

Scientists analyzed lunar rock samples that contain tiny, water-trapping beads of glass; these beads formed when magma erupted from the Moon’s interior billions of years ago, trapping water inside them. The scientists then looked at satellite data collected by an Indian lunar orbiter to check where these water-trapping glass beads are. The results, published today in Nature Geoscience, show that there are widespread “hot spots” of water-rich volcanic material beyond the Moon’s poles.

For years, scientists thought the Moon was completely dry. Then in 2008, scientists found water trapped in those glass beads of volcanic rocks collected during the Apollo missions in the 1970s. And more evidence has been found since then. But there are still questions about just how wet the Moon’s interior is. Today’s study tries to answer this question, using satellite data collected by the Moon Mineralogy Mapper instrument on the Chandrayaan-1 orbiter.

“The fact that they see this feature associated with the glasses tells us that there was indeed quite a bit of water in the interior of the Moon when these volcanic eruptions were occurring,” Anthony Colaprete of NASA told National Geographic.

The study doesn’t say just how much water there is, but it maps where these water-rich hot spots are — near the Apollo 15 and Apollo 17 landing sites, for instance. This information is useful because if people return to the Moon, they could mine the surface for water instead of carrying it all the way from Earth. Now we know where more of this precious resource is.