In the 1970s, the Apollo astronauts returned from the moon with tiny beads of volcanic glass they had picked out of the lunar soil. The beads are remnants of the moon’s early history billions of years ago, when eruptions spewed magma onto the surface. The magma, exposed to the vacuum of space, cooled rapidly. Some droplets froze as they fell, hitting the ground as glass.
These tiny beads became a lot more interesting in 2008, when scientists discovered they contained water. In 2011, researchers found that the beads contained similar amounts of water as some basalts on Earth, which form when volcanic rock from the planet’s mantle cools rapidly. For decades, scientists had thought the moon was a dry world. The clues inside the glass beads suggested a different story. There’s water on the moon, and some of it may still exist in ancient deposits deep within its interior.
But the Apollo moon rocks were only a sample. They could be anomalies, poor representatives of what really lies beneath the surface.
Ralph Milliken, a professor in Brown University’s geological sciences department, decided to widen the search. Milliken and his collaborator, Shuai Li, a researcher at the University of Hawaii, used satellite data to study numerous volcanic deposits across the lunar surface where water, if it exists, would be contained in glass beads like the ones the Apollo astronauts collected.