Water everywhere! (But not a lot)

September 25, 2009

 

Well, the news is out – and you read it here first! Carle Pieters, principal investigator for Chandrayaan-1′s Moon Mineralogy Mapper, published an article in Science that announces the discovery of much more water on the moon than anyone had suspected before.

Previously, Lunar Prospector and other spacecraft had detected thermal neutrons that are indicative of hydrogen, concentrated at the poles. Chandrayaan-1 completed the picture by detecting an infrared absorption signal that either indicates the presence of water or a hydroxyl molecule — the (OH)- ion that couples with H+ to form water. Either way, you’ve got all the ingredients you need for water.

There are many intriguing and exciting things about this discovery that call for followup. In a separate article, Jessica Sunshine of the Deep Impact mission reported an even more definitive observation that also show the concentration of water varying over the course of a lunar day! (N.B. A lunar day is 27 Earth days plus 7 hours.) Just like on earth, the “dew” is most concentrated during the lunar morning and then burns off. It then reaccumulates toward evening.

Nobody knows where this water has come from or what the mechanism is for its appearing and disappearing. The conventional wisdom was that water couldn’t possibly exist on the lunar surface, let alone be refreshed on a daily basis. When people have suggested that water exists on the lunar surface, they have assumed that it had to be deposited there over the eons by comets and that it would only be found in “cold traps” — permanently shadowed craters near the poles where the temperatures are so cold that molecules of water cannot escape to space. Now it seems to be everywhere. But it is more concentrated near the poles, so the “cold trap” idea is not necessarily completely wrong.

Before you get too excited, I should also say that the concentrations of water that the satellites found are extremely low: roughly a liter of water per ton of lunar soil. It remains a daunting prospect to extract such a tiny amount of water for human use. But still … as we said, maybe there is more at the poles, and maybe in really usable concentrations.

This result in no way upstages the LCROSS experiment, which I’ve written about before. It sets the table for LCROSS. So far we have only looked from afar for signs of water ice, but LCROSS will take us right there and try to dig the ice up. Also, as I’ve said before, only LCROSS can tell us whether there is any water beneath the surface.

Finally, it will be very interesting to see how this discovery affects the debate over where America’s manned space program should go next. The Augustine report, as you might remember, said that we need to increase NASA’s budget by $3 billion (from $18 to $21 billion) to get anywhere, and it highlighted two main options for what we can do with that money: “Moon First” or “Flexible Path.” I think the case for “Moon First” just got a whole lot better. However, the big political unknown is whether the case for either of them is strong enough to overcome the critics’ skepticism and get Congress to allocate the extra money.

But that’s a concern for another day. Right now, it’s fantastic to be able to  cross out the words “may be” and write the word “is.”

There may be water on the moon.

There IS water on the moon!

P.S. Some of the commenters on Richard Kerr’s article, which I linked to above, said that Science gave insufficient recognition to the Indian Space Research Organization (ISRO), which developed and launched the Chandrayaan-1 mission. They also resented the description of Chandrayaan-1 as a “defunct” satellite, although that is literally true. I think they have a point. Pieters’ article, of course, gives abundant credit to ISRO, because she was part of the mission team. However, the media coverage here has probably tended to downplay the fact that this was an Indian satellite. Some of the readers were congratulating NASA even though NASA had almost nothing to do with this mission. And though the satellite is defunct, it’s much more important to emphasize that the mission was a huge success. This was the mission that clinched the case for water on the moon. Period, end of sentence!

This entry was posted on Friday, September 25th, 2009 at 6:02 pm and is filed under Missions, Science. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.