NASA's "crash and splash" gambit dredged up water from a darkened lunar crater - but not nearly as much as scientists expected to find.

By J. Kelly Beatty

IF YOU LOOK UP "DRY" in a dictionary, you won't find the Moon's picture next to the definition - but it should be there. By the mid-1970s, the dusty rocks returned by six teams of Apollo astronauts and three Soviet robotic missions had all but certified that the stark lunar landscape contains no water whatsoever.

Yet comets do slam into the Moon now and then, bringing water and a host of other volatile compounds. Where does it all go? In 1979 geochemist James Arnold revived a radical idea first proposed two decades earlier: Some of the water from those collisions should become "cold-trapped" in the frigid floors of craters near the lunar poles, where - by a quirk of orbital geometry - the Sun never shines.

If water actually accumulates in these inky recesses, how can we tell it's there?

Read the rest of this article in the April issue of Australian Sky & Telescope.