A spacecraft that performed a choreographed, two-part dive into the lunar surface in October churned up detectable levels of water ice, NASA announced Friday.
The Lunar Crater Observation and Sensing Satellite, or LCROSS, chased a spent Centaur rocket stage toward the moon to observe the booster's impact into a permanently shadowed crater known as Cabeus near the lunar south pole. The satellite then crashed into Cabeus itself.
Before its impact, the main craft's spectrometers collected enough data from the Centaur plume to indicate the presence of liberated water. The spectra gathered by LCROSS, project scientist Anthony Colaprete said in a prepared statement, could only be reconstructed if water was assumed to be present in the plume. "No other reasonable combination of other compounds that we tried matched the observations," he said.
According to SPACE.com, Colaprete estimates that the spacecraft detected 100 kilograms—about 25 gallons—of water. Such stores could be invaluable for future lunar explorers, who could save vast amounts of launch weight by tapping into the moon's own water resources rather than bringing their own.
The mission, which began with a June launch alongside NASA's Lunar Reconnaissance Orbiter, sought to resolve long-detected hydrogen concentrations at the lunar poles, from which the presence of water had been inferred. But a similar impact by the Lunar Prospector spacecraft in 1999 failed to dig up sought-after water ice, which could remain trapped in significant amounts in the moon's shadowy craters.
A team of researchers announced in September that they had uncovered evidence from other spacecraft for widespread water distribution across the lunar surface, but in much sparser concentrations than what LCROSS found in Cabeus.
Photo of Cabeus crater floor and the impact scar left by the Centaur rocket stage: NASA