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NASA Briefs Preliminary Plume Findings from Moon Mission
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post Nov 14 2009, 06:08 PM
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QUOTE (centsworth_II @ Nov 14 2009, 06:41 PM) *
Right. I thought the 100kg was an estimate of what was actually seen in a narrow field of view and that they are not ready to estimate what was in the entire plume or in the entire excavated area.


I already see a discussion on what 100kg means is going on. 100 kg per 20x20kms crater means it's quite dry. But a narrow field would require a whole new line of calculations and investigations, which I don't see it will happen in the next several weeks.
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nprev
post Nov 14 2009, 07:44 PM
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Z, the crater diameter is actually 20-30 meters, not km.

Again, though, I can't see what these results really tell us other than that water & some other volatiles are in fact present. They may be able to set an upper limit on the amount present at this spot, but any further extrapolation would apparently require a number of assumptions.

That being said, it's still an important & exciting experiment. We are now certain that there is water in this region. How much is still anyone's guess.


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P Hayne
post Nov 14 2009, 07:44 PM
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QUOTE (Zvezdichko @ Nov 14 2009, 10:08 AM) *
I already see a discussion on what 100kg means is going on. 100 kg per 20x20kms crater means it's quite dry. But a narrow field would require a whole new line of calculations and investigations, which I don't see it will happen in the next several weeks.

The crater diameter is about 20 meters. This gives roughly 1-10 ppm water by volume, if 100 kg represents the total amount of H2O in the ejecta (which is uncertain).

( 3.14*(10 m)^2 * (2 m) = 10^4 cubic meters; (100 kg H2O) * (1 m^3 / 1000 kg) = 0.1 cubic meter H2O; (0.1 cubic meter H2O) / (10^4 cubic meters total) = 10^-5 = 10 ppm H2O )
( changing the depth-to-diameter ratio from 1:10 to 1:5 gives roughly 1 ppm H2O. )
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ngunn
post Nov 14 2009, 08:33 PM
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Well we've now got three estimates in the same ballpark. Converting to ppm: nprev 12ppm, myself 25ppm and P Hayne 1-10ppm.

I started wondering - if that were gold would we mine it? So with this thought here's a comparison from Wikipedia:

"Gold extraction is most economical in large, easily mined deposits. Ore grades as little as 0.5 g/1000 kg (0.5 parts per million, ppm) can be economical. Typical ore grades in open-pit mines are 1–5 g/1000 kg (1–5 ppm); ore grades in underground or hard rock mines are usually at least 3 g/1000 kg (3 ppm). Because ore grades of 30 g/1000 kg (30 ppm) are usually needed before gold is visible to the naked eye, in most gold mines the gold is invisible."
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Phil Stooke
post Nov 14 2009, 09:01 PM
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I've put together a little finder guide to the LCROSS impact site with an estimate of the SSC impact location. All of the images are from LCROSS except the big one © which is part of a DIVINER (LRO) map.

Phil

Attached Image


PS Well duh! My 'C' in parenthesis gets automatically turned into a copyright sign. However, anything I post on UMSF is intended to be public domain in its posted form.


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Fran Ontanaya
post Nov 14 2009, 09:52 PM
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But you are using estimates for pure, solid ice and a solid surface. Colaprete said that looking at the size of the crater that seemed unlikely.

Those 100kg minimum of H20 probably meant more than 0.1 cubic meters, and the average density of the ejected material could have been less than lunar rock.

Organics like methane yield water easily, their mass should count too.


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Holder of the Tw...
post Nov 14 2009, 10:27 PM
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I really appreciated Colaprete being willing to openly mention the possible other volatiles they may be seeing, pending final proof. He would have been well within his rights to say he was holding comment until the analysis was definitive. Now we know that hydrogen compounds in addition to water are probably available, along with sources of carbon.

QUOTE (ngunn @ Nov 14 2009, 02:33 PM) *
I started wondering - if that were gold would we mine it?


Clever! One should also mention that it will be a lot easier to bake water out of lunar soil then to extract metal from ore. It can be certain that at this concentration it will be better to mine water than import it. Based on some studies done about mars sample returns that examined the use of refueling on the surface, and given the energy requirements for lunar sample return are similar but smaller, it's possible to speculate about a sample return probe with rover, where the rover processed ascent fuel in addition to gathering samples.

Of course, it would have to be a big sample return mission, and you'd have to be pretty patient with the rover, but there might be enough science here to justify it.
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PFK
post Nov 15 2009, 12:00 AM
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Just out of interest - what would the total organic chemical content of the Centaur amount to? Plastics, wiring etc. Vapourise them via a collosal thud and all manner of fragments will fly.
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nprev
post Nov 15 2009, 12:08 AM
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That's an excellent point.


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Phil Stooke
post Nov 15 2009, 01:13 AM
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I don't know offhand but it's obviously very well characterized already. It's not a basis for doubting the results.

Phil


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P Hayne
post Nov 15 2009, 04:39 AM
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QUOTE (Fran Ontanaya @ Nov 14 2009, 01:52 PM) *
But you are using estimates for pure, solid ice and a solid surface. Colaprete said that looking at the size of the crater that seemed unlikely.
Those 100kg minimum of H20 probably meant more than 0.1 cubic meters, and the average density of the ejected material could have been less than lunar rock.
Organics like methane yield water easily, their mass should count too.

The 100 kg reported was based on a column abundance (# per-square-meter), derived from the H2O band depths in the near-infrared spectra. This represents water molecules only. However, this number is derived from a model fit to the data, so uncertainties are large, as is typical for remote sensing spectroscopy. Regardless, the order of magnitude result will likely stand up, meaning the uppermost layers of the cold traps are about as "wet" as predicted (c.f. Campbell et al, Nature, 2006; Siegler et al, LPSC, 2009). That is, it's pretty dry, but not hopeless. Also, don't forget that we're only sampling the uppermost ~1-5 meters (including the ground-based radar results), so there could still be slabs of ice below.

Perhaps even more interesting are some of the other compounds, including several organic volatiles, that were observed in the ejecta plume. An interesting take on the smorgasbord of volatiles likely to accumulate at the lunar polar cold traps, is provided by Zhang and Paige, "Cold-trapped organic compounds at the poles of the Moon and Mercury: Implications for origins" Geophysical Research Letters 36, L16203.
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tanjent
post Nov 15 2009, 04:41 AM
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Regarding the comparison of water to gold, remember that on the moon, water will be needed in much greater quantities than gold. This applies whether the need is for human consumption or, broken into its elemental components, as a fuel source. In the lunar environment, water would be more difficult to process than gold in one important respect - the gold wouldn't need to be constantly confined to prevent its escape to the vacuum of space. Any attempt to set up shop and utilize trace amounts of lunar water will have to invest heavily just in thermal insulation alone, otherwise those trace amounts are going to prove very difficult to corner. Remember those discarded Russian RTG's in Georgia that were located in the wintertime by hunters because they were surrounded by large circles of snow-free terrain? It's pretty hard to do industrial-scale work without generating waste heat, and at the local temperatures and vapor pressures prevailing in Cabeus, a little waste heat will quickly disrupt the delicate environmental balance that trapped the water in the first place.

This mission has told us a lot we didn't know. I'm intrigued by what these deposits can teach us when we determine where the water came from, and this should be answerable either by further work on the LCROSS data set or with some sort of sample return mission. But to significantly lower the costs of exploration we need at least a recognizable "dirty snowfield," not the Atacama desert.
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P Hayne
post Nov 15 2009, 04:44 AM
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QUOTE (PFK @ Nov 14 2009, 04:00 PM) *
Just out of interest - what would the total organic chemical content of the Centaur amount to? Plastics, wiring etc. Vapourise them via a collosal thud and all manner of fragments will fly.

A serious concern is the presence of hydrazine fuel from the Centaur rocket, which does have some poorly-characterized absorption bands in the near-infrared. From what I have seen, it might be possible to reproduce one of the bands attributed to water, by using hydrazine, but not all of the water bands. If anyone can dig up (or measure!) a decent hydrazine absorption spectrum, that would be very helpful. The best I have seen was from the 1950's and was basically qualitative (can't recall the author).
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nprev
post Nov 15 2009, 04:47 AM
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Did the Centaur actually have hydrazine? The main engines use LOX & LH2, and attitude control was provided during cruise by the LCROSS spacecraft itself.


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P Hayne
post Nov 15 2009, 04:55 AM
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QUOTE (nprev @ Nov 14 2009, 08:47 PM) *
Did the Centaur actually have hydrazine? The main engines use LOX & LH2, and attitude control was provided during cruise by the LCROSS spacecraft itself.

Yes.
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