Lunar orbiters such as India’s Chandrayaan-1 spacecraft and NASA’s Lunar Reconnaissance Orbiter (LRO) recently detected water icy on the floor of some of the south polar craters, but no one is sure exactly when or how that ice got there. A new study by researchers from Brown University and NASA’s Goddard Space Flight Center suggests while a majority of those ice deposits are likely billions of years old, some may be much more recent.

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