Tuesday, March 2nd, 2010
Now that it doesn’t matter any more, the amount of water on the moon just keeps going up and up and up. Last October, it was a glassful of water per football field of soil. In November, it was twelve 2-gallon buckets of water in a 30-meter wide crater. And yesterday, we found out that we were talking about 600 million tons of water spread over forty craters near the moon’s north pole. According to Paul Spudis, that amount of water, if you converted it all to rocket fuel, would be enough to launch one space shuttle per day for 2000 years.
By the way, my first few words (“Now that it doesn’t matter any more”) were intended to be facetious. Of course, it is common knowledge that the Obama administration last month abandoned the plan (Project Constellation) to send human astronauts back to the moon in the early years of the next decade. So for the short term, yes, it doesn’t really matter how much water there is on the moon.
But for the medium and long term, of course it matters. First of all, there are going to be many opportunities to send robotic precursor missions to the moon over the next decade. In fact, NASA will have more money for this kind of mission now that we have given up on the struggling Constellation effort. There’s a strong case to be made that this is exactly the kind of mission we should be thinking about at this point anyway. The sheer volume of water is such a surprise, and there are so many mysteries about where it comes from and how it moves around. We really should be focusing on unraveling this science story now.
That’s the medium term. And for the long term, humans will go back to the moon eventually. If not NASA, somebody somewhere is going to figure out that the way to establish a permanent presence in space is by using resources that we find in space — and right now, the number one resource in terms of ease of access and usefulness is lunar water.
Now for the details. The latest surge of articles on lunar water stems from a press conference yesterday at the Lunar and Planetary Science Conference in Houston. Just as October was Carle Pieters’ big moment and November was Tony Colaprete’s moment in the sun, this was Paul Spudis’ turn to shine. He has been telling us for several months that he had some really cool data that he couldn’t tell us about officially, because the magazine he was trying to publish in (whose title begins with “S” and ends with “cience”) would not let him. He has apparently given up on publishing there, and so now he is free to talk.
Paul was the principal investigator on Mini-SAR, a radar probe that flew on the Indian Chandrayaan-1 mission. This is the same kind of instrument that made the very first tentative discovery of water, on the Clementine mission, back in 1994. But now it’s a whole lot more sensitive, especially in terms of spatial resolution. Spudis identified at least 40 craters in the north polar region with really significant quantities of water ice. There are also nearby craters that look similar yet don’t have ice in them, so it will be a real challenge for scientists in the future to explain why some do and some don’t. The craters are too small to have official names, but if you have your moon maps handy, some of them are small sub-craters of Peary and Rozhdestvensky. (I’m not sure if “sub-crater” is really a word, but if not I just invented it.)
While Spudis’ report was probably the biggest news, Tony Colaprete of the LCROSS mission also revealed some new information. That is the mission that crashed into a crater near the South Pole, called Cabeus A, and found proof of water and other volatile compounds, such as carbon dioxide and simple hydrocarbons. Now Colaprete is reporting that some of the ice was in crystalline form. This is the sort of thing that might make non-savvy readers shrug their shoulders and say, “So what? Isn’t all ice crystalline?”
Well, no. There are lots of different forms of ice, and one possibility was that the ice might be in an amorphous form, scattered through the dirt not in the form of crystals but just as a sort of alloy with the other minerals. If you have ice crystals, that means you at least have little bitty chunks of more or less pure ice. That’s good if you ever want to recover the ice and make rocket fuel out of it. It would be even better if you actually had frozen ponds of the stuff, but I don’t think anyone expects us to get that lucky.
One more comment — the more water you find, and the more other volatile compounds you find, the more likely it becomes that they came from off-world. If the ice came from meteor or asteroid impacts, then there is also a good chance that there are ice deposits underground, possibly covered up by younger, drier material. So there may be even more ice than we know about at the moment.