Thursday, September 24, 2009

No genuinely free water on the Moon, it would seem...

The ambiguity of "free" in my title is deliberate. The traces of water detected by that inspired Indian lunar probe are not of course  free water, in a chemical sense, but chemically-bound, non-wettening "water".

 Is that a water-diviner in his hand? If so, then happy-hunting..

Even my non-scientific wife was quick to realize that, watching last night's news, even if the media reports elsewhere conjure up visions of future moon colonists tapping into an abundant supply.  Moonshine!

Being chemically-bound, whether weakly or strongly,  it's hardly free for the taking either. The expression "getting blood out of a stone" springs to mind.

Here's what I sent last night to the Times in response to that  trumpeting  headline re there being a litre of water per tonne of lunar soil. (One feels that "water" should have been enclosed in quotation marks in the Times's article).

To say there is "water" on the Moon when it's there as the hydroxyl radical/ion is a little misleading, as others have pointed out. It's like saying that farmer's lime, calcium hydroxide, is a potential source of water. True, in a manner of speaking, but you would have to get it red hot to drive off water as steam, as in lime-furnaces, and then have a means of cooling and condensing to get liquid water. It may sound easy in principle, but the practical aspects of attempting this on the Moon are formidable. One would need an abundant supply of energy - probably tens or hundreds of square metres of solar panels to generate megawatts of electricity.

Why not get the Sahara green first - to create biomass and reduce CO2? Huge problems to overcome, yes, but if we can't lick that problem, what hope is there of colonising the Moon or Mars on a realistic timescale?

September 24, 2009 11:10 PM BST on

"Hydroxyl", note, is not a molecule, as the report would have one believe. Being simply OH, with an unpaired electron, it would be a free radical, with no independent existence, and a lifetime of seconds at most if generated in the atmosphere by, say, cosmic ray bombardment. Most "OH" in rocks is, of course, present as negatively-charged hydroxyl ions, accompanying positively-charged metal ions, eg aluminium.

Aside: well done, btw,  Times for finally adding a time and date stamp to readers' comments,  and for a much-speedier moderation than before. The BBC-style facility for expressing approval is also cute.  It even survives cut-and-pasting here, apparently as a live-link - see the blue font above!  Shame though that one's comments are not accessible to search engines. The world wide web depends on linking, you know, if only for information-retrieval. Vanity has nowt to do with it, of course...

Update: Friday 15:15 pm.  Had some further  thoughts on the inconclusive nature of the chemistry after reading the New Scientist's feature:  Have just sent the following:

"Hmmm. So the signal could have come from water or from the "OH molecule". Leaving aside the faulty nomenclature - OH is not a molecule, but is either a free radical if electrically neutral, or a negatively- charged ion -  it seems a bit of a liberty to lump together two entirely different chemical species in this manner. The discovery of  H2O would indeed  be exciting, even if strongly adsorbed to minerals. But "hydroxyl", presumably as mineral hydroxides, would be an entirely different matter, requiring somewhat high temperatures in most cases if  desiring to drive off molecular water, which would then have to be cooled and condensed. Most of the hydroxides of predominant minerals in the Earth's crust - magnesium, calcium, aluminium etc-  hang onto their oxygen and hydrogen quite firmly, needing red heat or higher to dissociate into oxides and steam.

So it's somewhat premature surely to report that "water" has been discovered. On the basis of available evidence, none of which can be described as "hard",  what's been discovered are  oxygen atoms that are bonded to one or possibly two hydrogen atoms with a strong attachment to a mineral matrix given they are able to survive solar heating in a vacuum. Alternatively, and less usefully from the point of view of harvesting lunar water, the signal is picking up a temporary association, ie  the turnover model, which would explain why the discovery did not come earlier from study of Apollo-mission rocks"

Update  Sep 25 21:17 : See also "How could astronauts harvest water on the Moon" - latest article in New Scientist.

No comments: