Scientists have now confirmed what was long suspected: that ice does indeed lurk at the bottom of Shackleton Crater, on the Lunar south pole. The crater is named after the legendary polar explorer Earnest Shackleton.
Using the instruments aboard the Lunar Reconnaissance Orbiter, or LRO, the scientists measured the albedo of the crater floor. Since the reflectivity of ice is known, this method would reveal any ice on the surface. Subsurface ice, which may exist in greater quantities, would require a coring to detect.
How can ice survive on the moon? The polar night is obvious, but what about during the day? Sunlight is so strong on the moon that any ice would have sublimated away. The reason it can hide here is the crater's unique structure: it is located directly on the south pole, and it is very deep. This means that sunlight can never reach the bottom. The ice hides in the shadows.
This ice would have been deposited over eons by comets. The total distribution would have been nearly even across the moon; however, most of it would long ago been sublimated away by the sun. Only in pockets of permanent shadow, such as Shackleton crater, can the ice survive.