One interesting question is: to what degree does the estimated concentration of hydrogen compounds in the plume match the concentration of hydrogen calculated from the neutron spectrometer measurements of Cabeus from LRO and Prospector? The neutron spectrometer measurements are averaged over a larger region, so if the concentration in the plume is smaller, it seems to imply larger patchy concentrations elsewhere in the crater. (I think Colaprete made this point in press conferences before the impact.) If the concentrations are about the same, then we can possibly extrapolate what the neutron spectrometer measurements mean in terms of specific compounds.

I don't have the LRO results. This paper, which interpreted everything in terms of implanted solar hydrogen, gave 1500 plus/minus 800 ppm by weight hydrogen from Prospector data.

If entirely in the form of water - just for the sake of argument - that would give you between 6.3 and 20.7 parts per thousand (or 6,300 to 20,700 ppm) by weight H2O. In reality we already know the hydrogen exists in various forms and compounds.

Just to be clear, when I mentioned the organic content of the Centaur I certainly didn't mean to imply this would have implications for water measurements. I was thinking more of the "C-H" compounds they alluded to.
I'd agree entirely that it would be possible to make an inventory of this that would indicate how much "stuff" could be generated. And if this total is way below what is seen on the organic front then there's no issue - and I presume it is. Predicting what would be generated by such a powerful impact is, however, much harder. In reality, I suspect, all manner of small fragments will fly.

Most of the organics on the booster would presumably be wire insulation: PTFE, Kapton, etc. Would it be reasonable to assume that most of this stuff was subjected to high heat & subsequently decomposed into simple organics almost instantaneously during the impact?

IIRC, there's a fair amount of carbon in lunar soil already, and definitely a lot of oxygen. There might be a detectable excess of hydrogen and nitrogen from breakdown of the booster's wire insulation, but according to Phil this has been "tared out" of the observations.

There is also a lot of doubt about how a manufactured object behaves in an impact. A rock hitting the Moon at several km per second behaves in ways we understand fairly well, but how does an impacting rocket stage behave? Some of its kinetic energy is used up bending metal. The top end of the impactor may not hit the surface at the same speed the bottom end did due to the complex behaviour of the structure. It's not as simple as a shock wave moving through a rock. I am not so sure that a bundle of insulated wires is going to be vaporized. We don't know a lot about this situation. I think these kinds of uncertainty generally act to reduce contamination of the type discussed here, but I expect we'll see more experiments on the ground to try to get a better handle on it.

Phil

Note that the impact was at only 2.5 kps.

http://lcross.arc.nasa.gov/rationale.htm

And it was not expected to vaporize more than 10% of the ice. Instead, they were counting on the Sun to do that.

--Greg

New scientist has confused me. I know I shouldn't put too much faith in what they report these days but they've said:

This is from their report on the Lunar Exploration Analysis Group meeting, so I was hoping for some interesting tidbits, but I'm just confused! Is the water content several percent, or the hydrogen content? Does anyone know of any other reports from the Lunar Exploration Analysis Group?

I'll spare you my opinion of the subject publication...

I think it's premature to discuss the LCROSS results before a peer-reviewed paper is published. IMHO, the LCROSS team didn't do anyone any favors announcing their preliminary results at a press conference.

I think you're right!

I disagree. The press conference did no harm and gave the public, who paid for the mission, exactly what they needed. This mission was funded, by the way, by the Exploration Systems Mission Directorate, not the Science Mission Directorate. The papers and conference reports, when they appear, will give the science community what they need.

The New Scientist article seems to plainly say that the hydrogen concentration, not the water concentration, was several percent, but obviously any report in a popular magazine should be viewed with due skepticism.

Well, I have some residual concerns about the detection methodology, and I don't think anyone knows if the amount of water detected was useful for resource exploitation or just a scientific curiosity. I'd think the public deserves the answer to that basic question.

I think you all may find the comments of William Marshall of Ames Research Center, as published in the New York Times, interesting.

The Wet Side of the Moon

I was particularly intrigued by the statement, "Almost as surprising as NASA's announcement is the lack of attention it has received."

Neat graphic as well.