Unless you’ve been in hibernation through the winter months, you have probably heard that water has been discovered on the moon. It’s not as if water wasn’t predicted to exist at the bottom of the coldest craters, it’s just that there appears to be a lot more than scientists ever dreamed.

And on Thursday, NASA released some details about how much water ice has been detected in the north lunar pole: 600 million metric tons of the stuff, stashed away in 40 craters.

As “600 million metric tons” doesn’t mean very much, we can convert that into less R-rated units: approximately 158 billion US gallons. Even better: enough water to fulfill all of Seattle’s water needs for three years.*

Yes, that’s one huge bucketload of water.

This new announcement comes hot on the tail of a series of water discoveries on the lunar surface. Everything from the discovery of “significant quantities” of water ice after NASA’s LCROSS suicide bombing of a shady crater to a possible solar water production mechanism that creates a thin layer of ice all over the lunar landscape. Water appears to be turning up everywhere on the moon. Not bad considering it was once thought to be bone dry.

Less than a year ago we were hoping there might be a puddle of frozen water in the coldest craters, now we’re talking about large-scale stores of ice in quantities that could supply a large US city! Wow.

VIDEO: NASA just smashed the LCROSS and spent Centaur rocket into the moon in a search for water on the lunar surface. Did it live up to the hype? James WIlliams takes a look.
This latest discovery comes from an instrument that was carried aboard the Indian Chandrayaan-1 lunar orbiter before it was lost in August, 2009. NASA’s Mini-SAR team found these 40 craters each containing water ice at least 2 meters deep.

“If you converted those craters’ water into rocket fuel, you’d have enough fuel to launch the equivalent of one space shuttle per day for more than 2000 years,” said Paul Spudis of the Lunar and Planetary Institute, who obviously tried really hard to think up a suitable analogy (it’s good, but I think my Seattle one was better).

The excitement surrounding this discovery is tangible, but Spudis points out another intriguing possibility: Does the moon have its own water cycle?

“So far we’ve found three types of moonwater,” said Spudis. “We have Mini-SAR’s thick lenses of nearly pure crater ice, LCROSS’s fluffy mix of ice crystals and dirt, and M-cube’s thin layer that comes and goes all across the surface of the Moon.”

The moon does appear to contain three different “flavors” of water ice. Some pure water appears to have been deposited on the lunar surface (perhaps by passing comets). Some appears to have formed under the surface, mixing with lunar material. And the rest appears to have been formed on the surface through interactions with the solar wind.

Amazingly, these preliminary results indicate that there is also a migration of water from equatorial regions to the lunar poles, pointing to some kind of water cycle. Yes, scientists are seriously contemplating a lunar “hydrosphere.”

Unfortunately, just because there’s water on the moon, it’s not a good enough excuse to send astronauts back there any time soon. Despite dreams of self-sustaining colonies and premium lunar condos, this is one water supply we may not get to taste for a while yet.

*Based on Seattle’s water consumption of 140 million gallons per day in 2004 (140 million gallons × 365 days = 51.1 billion gallons per year) [source] Note: I’m not advocating a plan to supply Seattle with moon water, because that would be silly.