The big science story this week was the confirmation that the moon is covered in water. And not just in the shadowed, polar craters where scientists suspected it, but all over. Water on the moon--that has to be great news, right?

Not really. While unexpected discoveries are always interesting scientifically, this one is actually bad news for space exploration. It would have been better if lunar water wasn't quite so ubiquitous.

When I previewed NASA's LCROSS mission last March, I noted that its purpose was not really in determining whether the moon had water, but in determining how the water was distributed. Even though LCROSS is still scheduled to smash into the Moon's surface in a couple weeks, it now seems likely that it will only confirm this week's findings: that there are trace amounts of water everywhere on the moon.

For human exploration, highly concentrated deposits of ice would be a much more useful distribution. The possibility of mining water on the moon has often been cited as both the means and the end for sending people back to the moon (Bill Stone, for example, has been a big proponent). Even with the possibility of big deposits, though, I was always skeptical that mining lunar water ice could ever be efficient enough to be worthwhile. Now, it seems unlikely that any usable amount of water can be extracted from the surface. Geologist Robert Clark estimated that one ton of lunar soil might yield "as much as 32 ounces of water" (a little less than a liter). That means it will take a lot of work to get a little liquid, even with the help of innovative suction robots.

I'm now interested to see how this finding is used as political spin. Back in the Bush years, NASA's Constellation program promised a fully-functioning moon base within two decades (the program continues to move forward, but its future remains in limbo). Constellation's ultimate destination, at least in theory, was Mars. But, in practice, the moon quickly became the primary target. The agency then needed to come up with a bunch of justifications for going there, after the fact. The prospect of mining lunar water, always seemed l one of these. Regardless of the impracticality of collecting it, the water finding may energize Moon proponents. A Space.com article declared that "Water Makes Moon Suddenly a More Attractive Destination." The New Scientist similarly raised hopes:

Newly confirmed water on the moon could help sustain lunar astronauts and even propel missions to Mars, if harvesting it can be made practical.

In this summer's Mars special report, we examined whether going back to the moon before Mars is even necessary. While a moon program may make us better prepared for the longer and difficult journey, it could easily turn into a wasteful disatrction that eats up valuable time and resources. Frankly, the chance of finding evidence of life on Mars will always make it a more attractive destination than our close, but definitely dead, satellite. And if it's water you're really after? Mars has more of that, too.