The lunar maria, 'seas,' are the only surface features on another astronomical body that we can easily recognize with the naked eye. But (so far as I know) no one ever thought to name them or map them till the telescope showed that they were indeed surface features on a world. And they had barely been named before it was realized that they were not seas at all, but dry plains.
The Moon has been getting dryer ever since. Until yesterday, when news came out that a research team using data from three spacecraft has shown that the Moon apparently does have water after all, in fact quite a bit of it, though very thinly dispersed as a nano-rime on surface rock grains. Moreover, the water seems to migrate toward the poles, suggesting that it might be in greater concentrations there.
I saw the story in yesterday's LA Times, dead tree edition. It is not up yet at Sky & Telescope, but it is up at the Bad Astronomy blog.
Of course there is already speculation about where the water comes from. Perhaps it is primordial, perhaps deposited by comet impacts over the eons. But coolness points for the theory that the solar wind is constantly breeding the stuff, hydrogen living up to its name by sometimes binding to oxygen atoms in the lunar surface.
But this is also one of those times when the March of Science can be exasperating. There wasn't a whole lot of hope for lunar water even back in the pre-Apollo books I read as a kid, and Apollo ended whatever prospects there were for anything like a subsurface permafrost layer. The possibility of ice hung on in a few perpetually shadowed craters, but my recollection is that even this hope had pretty much - so to speak - evaporated. Just back in May I blew off the Moon, largely for this reason.
Now, if these new findings hold up, lunar science is doing an Emily Latella on us: 'Oh. Never mind.'
But it gets better. Two of the three spacecraft whose data provided this information weren't even exploring the Moon; they just happened to pass through the neighborhood. (The third is Chandrayaan-1. I completely missed the news that India launched a moon probe; what a cool way to find out.) But just to add to the weirdness, one of the passers-by was Cassini, which hasn't been anywhere near the Earth-Moon system since it did a flyby in 1999, two years after it was launched. So that data was pretty much sitting on a hard drive somewhere, until someone decided to pull it up and look at it.
So the whole thing is wonderfully contrary and serendipitous. How much it affects the prospect of Doing Stuff on the Moon, I have no clue. On the one hand, 0.1 to 1 percent is quite a bit; at least a few glasses of water from every ton of moon rubble, and perhaps a couple of jugs of it. And baking it out of the rock, then freezing the vapor, doesn't seem hard to do on the Moon, given a pressure vessel. On the other hand, that is a lot of rock you'd have to bake to get a steady supply of water for, say, rocket fuel.
But in any case, the prospects for recoverable water on the Moon seem a lot better today than they did the day before yesterday. And much more important in the great scheme of things, even the prosaic, touched-already Moon has not lost its ability to surprise and enchant.