From: henry@zoo.toronto.edu (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Water on the Moon
Date: Fri, 8 Dec 1995 15:58:22 GMT
Organization: U of Toronto Zoology
Lines: 38

In article <c67cb$d24.158@kirk.microsys.net> cgray@kirk.microsys.net (Charles Gray) writes:
>    Has there ever been any evidence of water, or hydrogen being
>present on the moon in any great quantity?  I know that apollo never
>found much, but considering that we have something less then a dozen
>samples from a land area somewhat greater then africa in surface area,
>that's probably not a good starting point for a theory.

Unfortunately, one thing that *is* abundantly clear from the Apollo samples
is that the Moon was very thoroughly baked early in its history.  So it is
vanishingly unlikely that any significant quantity of volatiles survived
the Moon's formation.  Any major concentration of hydrogen/water/etc. on
the Moon must be the result of material arriving later and somehow being
preserved.

The best bet for lunar volatiles is frozen deposits in permanently-shadowed
areas near the poles.  This idea has received a major boost from radar
detection of (what appear to be) ice deposits near the poles of Mercury (!).
The Clementine bistatic-radar experiment apparently gave strong hints of
similar ice deposits at the lunar south pole, but the details have not yet
been published.  (Publication, in Science, is reported to be imminent.)

It is also marginally possible that there are small amounts of volatiles
being released by small-scale, localized volcanic activity.  The evidence
is poor but it's not out of the question.

In general, Charles is correct that our sampling of the Moon is inadequate
to say much about possible ore bodies.  Ores are, almost by definition,
lucky accidents, the result of extreme cases, and our limited sampling of
the Moon gives a reasonable understanding of average conditions but tells
very little about extremes.  Unfortunately, what we know about averages
does indicate that the odds of major concentrations of volatiles are poor.

The definitive way of finding lunar hydrogen sources would be to fly
gamma-ray/neutron spectrometers in low lunar orbit, and the Lunar
Prospector mission is planning to do that in 1997. 
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: lunar resources (was Re: NASA's $3 billion ET Moonbase)
Date: Fri, 5 Jan 1996 17:04:33 GMT

In article <4ci8oa$6d6@lace.colorado.edu> fcrary@rintintin.Colorado.EDU (Frank Crary) writes:
>>Ah, but there is sunlight not very far above the surface there.  You can
>>probably build your solar-powered processing facilities on the crater rims.
>
>On the other hand, this could be an argument _against_ the
>existence of ice in polar craters. Part of a polar crater
>is never in direct sunlight, so you might expect ice to
>remain there. But the rim and other parts of the crater
>would be in sunlight. They would get moderately warm,
>and radiate energy in the infrared...

Indeed so.  This effect is severe in small craters, where the warm rim
is quite close to any part of the interior.  Fortunately, the scaling
works the right way:  bigger craters have colder bottoms, because rim
height does not scale up as fast as diameter.

If there can be ice in polar craters on Mercury -- and it's difficult to
explain the recent radar images in any other way -- then the Moon should
be okay.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Lunar Fuels (Was Re: NASA's $3 billion ET Moonbase)
Date: Sun, 7 Jan 1996 02:18:46 GMT

In article <4ck8ag$54@cloner2.ix.netcom.com> greason@ix.netcom.com(Greason) writes:
>...Even if lunar polar ice is found, hydrogen is likely to
>be too valuable to throw away -- and the contamination of the Lunar
>vacuum is going to be more severe than with these "oxygen + sand"
>exhaust rockets).

Actually, light gases are probably less persistent than heavy ones,
so there might be a mild preference for hydrogen-containing exhaust
on this particular criterion.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: Sputtering review (was Re: Water on the Moon)
Date: Tue, 9 Jan 1996 18:16:17 GMT

> ...sputtering by radiation is a major mechanism
> which should REMOVE accumulated ices in the Moon's shadowed spots.
> The existence of ice depends upon whether the rate of accumulation
> through comet impacts beats the rate of destruction by sputtering and
> sublimation...

Actually, there is an additional complication:  burial by impacts.  The
sputtering problem has been known for some time, and is generally thought
to be moderately serious for ice that's actually on the surface.  However,
the lunar surface gets stirred by impacts quite a bit, and this could
bury a substantial fraction of the ice.  Burial would eliminate sputtering
and substantially reduce sublimation.

The existence of ice at Mercury's poles is a fairly strong hint that it
ought to be possible at the Moon's poles.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: lunar resources (was Re: NASA's $3 billion ET Moonbase)
Date: Tue, 2 Jan 1996 23:43:56 GMT

In article <4c52uo$61g@peabody.Colorado.EDU> buckley@refuge.Colorado.EDU (Charles Buckley) writes:
>>Actually, a slightly less drastic version of this, vapor-phase pyrolysis,
>>involving heating to the vaporization point but not to ionization, is
>>taken seriously as a lunar-resources extraction process.  Solar energy is
>>cheap on the Moon, half the time. 
>>
>  I have also seen suggestions of using vacuum pyrolysis also. It would require
>temps of about 200-600 degrees C...

That's just for volatiles.  Vapor-phase pyrolysis involves going much
higher, to thousands of degrees, to do things like cracking oxides for
oxygen.  It has problems, but it's a serious concept.  It has the major
virtues of being simple and of not requiring recycling of chemicals;
the chemical processes tend to be complex and to require quite efficient
recycling.

>To extract water, you would need to crank
>that up to about 1000 degrees C. But, you would only net about 10ppm...

It is currently thought that there is no native water on the Moon, period.
The small amounts released in heating experiments appear -- based on
considerations like isotope ratios -- to be Earthly contamination of the
samples.  Native hydrogen comes off as hydrogen. 

>  ...I worry the the process to gather the regolith will release
>these materials since they are not chemically bound to the regolith...

The regolith has been "gardened" very extensively by meteorite impacts. 
In fact, that's the only reason why there are volatiles throughout the
soil; the solar wind penetrates only the top micron or so of the soil
surface.  A bit of excavation isn't going to release anything that impacts
haven't already released. 

>These
>materials are in such a trace amount that the process to mine them would
>have to be nearly 100% efficient...

Not really.  Inefficiency is (usually) a percentage loss, not an absolute
loss.  Absolute losses would be devastating to extraction of trace amounts,
but percentage losses are just a nuisance.
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: lunar resources (was Re: NASA's $3 billion ET Moonbase)
Date: Tue, 2 Jan 1996 23:28:58 GMT

In article <81977-820395285@mindlink.bc.ca> Nick_Janow@mindlink.bc.ca (Nick Janow) writes:
>[volatile extraction by heating]
>Yes, it should work well enough to be worth modifying the mining/refining
>equipment to capture the released volatiles.  However, as a means of
>extracting "all the carbon, hydrogen, nitrogen and nobel gases needed for
>life support" as Karen proposed, I don't think a high enough efficiency is
>likely for such a simple method...

What is it that you're skeptical about?  Heating is nearly 100% efficient
at extracting solar-wind volatiles from lunar soils, at least in the lab.
It's the single commonest technique for *measuring* the volatile content,
in fact.  At 700C, essentially all of the hydrogen and helium are out, and
significant fractions of the other volatiles.  At 1200C, only quite small
fractions remain in the soil (as confirmed by other methods).

Now, there are admittedly questions to be asked about doing this on an
industrial scale, but it's hard to imagine a method that is likely to be
seriously superior, given its simplicity, the ability to concentrate the
volatiles by just compressing them (a *lot* easier than getting them out
of a very dilute solution, for example), and very high extraction
efficiency.  The only real trick is how to heat large quantities of lunar
soil quickly, given that it is a pretty good thermal insulator; various
methods have been suggested. 

Whether the quantities of volatiles obtained by this method are adequate
for life support is another question.  The hydrogen, at least, is probably
adequate for "makeup" supplies to an efficient recycling system.

>There are quite a few potential mechanisms for failing to release 100% of
>the volatiles, and failing to capture 100% of the released volatiles...

As noted above, given adequate heating, release is known to be circa 100%.
Capture is admittedly an issue, when doing this on an industrial scale.

>...the loose binding of the volatiles means that
>release would start to take place as the dust is mined, meaning loss unless
>volatile collection started at the scooper...

I find it hard to take this seriously.  If a bit of mechanical handling
were enough to release volatiles, there would be little or no volatile
content in the bulk soil -- it would all be in the top micron or so of the
soil surface, and we could forget about practical extraction.  In fact,
most of the volatiles are tightly bound enough that they remain in the
soil when it is churned violently by meteorite impacts.  That's why there
are volatiles throughout the soil (or at least the upper layers, which are
all we've sampled well). 

Bear in mind, also, that all our estimates of volatile content are based
on dust that has already been handled.

>The dust would probably need
>thin spreading and agitation to speed release of the gases...

Possibly an issue, although it is somewhat porous already and we're not
talking about large quantities of gas.  Thin spreading may be needed in
any case, depending on the heating scheme.

>...It might need crushing if the atoms have been adsorbed into
>fine cracks in the soil particles...

It's not worth it.  The gas content is essentially entirely in the outer
micron or so of each soil particle.  In fact, it is probably worth
screening the incoming soil and passing only the fine stuff through the
extractor; the larger particles and rocks have minimal volatile content
by comparison, since their area/mass is so much lower.

>Is heating to several hundred C be
>enough to overcome adsorption of 90%+ of the atoms?

See above.  For more detail, see the relevant papers in "Resources Of
Near-Earth Space".

>What about the
>chemical reactions at elevated temperatures (reacting with free iron, etc)?
>Some of these mechanisms might only reduce extraction by a few percent, but
>there could be quite a few loss mechanisms, all adding up.

As mentioned above, since this extraction method is the usual one used to
measure volatiles in lunar soils, and since it is consistent with results
obtained by other means, this is not a problem.

>I suppose it was just the blithe assumption of economical 100% extraction
>of resources from an ore rated in ppm (or is it ppb?) that bothered me.

In this case, it appears to be pretty much justified.

>Has enough data been collected on lunar soil to form a reasonably accurate
>estimate of how much volatiles can be extracted by simple heating and
>agitation?

See above.  Nearly every estimate of volatile content that you see 
published was obtained by simple heating.

What isn't well known, however, is the variation.  The general volatile
content is reasonably consistent over the Apollo sites, but there are
hints of regional differences.  It is likely on general principles that
the content is lower at high latitudes -- because the solar wind is
roughly in the plane of the lunar equator, so wind per surface area is
maximum at the equator -- and a bit lower on the nearside than on the
farside -- because passages through Earth's magnetotail cut into exposure
time on the nearside -- but there is no solid confirmation of this.  Local
magnetic fields might have a significant concentrating effect, and the
chemical composition of the soil likewise might be a factor.  We have a
good idea about average surface properties but little information on
variability. 
-- 
Look, look, see Windows 95.  Buy, lemmings, buy!   |       Henry Spencer
Pay no attention to that cliff ahead...            |   henry@zoo.toronto.edu

Newsgroups: sci.space.history,sci.space.policy
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Return to the moon...Why not yet and when are we finally gonna do 
	it?
Date: Sun, 27 Dec 1998 22:41:42 GMT

In article <7640qv$6s6@lace.colorado.edu>,
Frank Crary <fcrary@rintintin.Colorado.EDU> wrote:
>>...And the neutron data from LP say that the ice is buried, not
>>right on the surface.  (There was reason to expect that anyway; surface
>>ice probably would not be stable on geological time scales.)
>
>In that case, _I've_ missed something subtle. In what way did the
>LP neutron data say that the ice is buried? Last time I checked,
>the instrument didn't provide any data on the depth of the ice...

According to the Feldman et al paper in the 4 Sept Science, you can get
some idea about burial depth by looking at the relative changes in the
number of epithermal neutrons and fast neutrons.  Because hydrogen's
neutron-scattering cross section falls as energy rises, at high energies
the oxygen in dry regolith scatters as effectively as the hydrogen.  So
buried hydrogen is partly hidden at high energies, but still visible at
epithermal energies.

LP saw strong hydrogen signatures at epithermal energies, but no
detectable signature at high energies.  So the hydrogen is buried.  If
you assume pure ice under dry regolith, the burial depth is about 40cm.
Different models of what's down there would give different numbers.
--
Mass-market software technology has |  Henry Spencer   henry@spsystems.net
been deteriorating, not improving.  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Water on Moon and Mars question
Date: Mon, 15 Jan 2001 18:32:26 GMT

In article <93thlk$edh$1@newsg1.svr.pol.co.uk>,
Dave H <Dave@Ihatespam.com> wrote:
>...I was wondering if a tundra-type perma frost could exist on the Moon
>or better still Mars...

Well, the lunar polar hydrogen probably *is* permafrost, i.e. a mixture of
ice and soil.  That aside, almost certainly there is none on the Moon.
Lunar Prospector would have detected it.

It's very likely, although not absolutely proven, that there is permafrost
in most high-latitude areas on Mars.  Near the equator it's too warm.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Water on Moon and Mars question
Date: Tue, 16 Jan 2001 22:19:09 GMT

In article <3A63A2F4.94E8B701@indra.com>,
Charles R Martin  <crmartin@indra.com> wrote:
>> Well, the lunar polar hydrogen probably *is* permafrost, i.e. a mixture of
>> ice and soil.  That aside, almost certainly there is none on the Moon.
>> Lunar Prospector would have detected it.
>
>That's a little overstrong, Henry.  Neutron activation certainly detected
>plenty hydrogen...

Um, did you read what I said?  Certainly LP *did* detect lunar polar
hydrogen, by its neutron signature.  The conclusion that it's probably
permafrost is based on the LP neutron results -- which indicated hydrogen
at shallow depths, not right on the surface -- and on ample earlier
theoretical work indicating that surface ice is not stable for very long.
Impact burial is virtually certain to have mixed in regolith, to the
extent that it wasn't mixed in already.

The "that aside, almost certainly none" is based on the fairly negative LP
neutron results elsewhere, and the implausibility of deeply-buried water
on a severely dry body with a warm interior.

>and they're not sure where Prospector actually impacted so
>they may not have been looking in the right place.  (Or it might have impacted
>on a dry spot.)

The negative results of the LP impact experiment tell us nothing either way.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Water on Moon and Mars question
Date: Tue, 16 Jan 2001 22:10:52 GMT

In article <9403ri$c3v$1@newsg1.svr.pol.co.uk>,
Dave H <Dave@Ihatespam.com> wrote:
>I think that even at the equator regions on Mars and even the Moon if you go
>deep enough you may find the frozen water, perma-frost of ice and soil.  The
>higher temperatures that would occur at the equator would mean that you
>would have to go deeper to find it because a thick insulating overburden of
>soil would be needed to protect it from being evaporated.

Trouble is, on Mars and even the Moon there *is* heat flow out from the
interior, and so temperatures eventually rise as you go down.  (For the
Moon, this was confirmed by the Apollo heat-flow instruments placed down
the core-drill holes -- the rise is easily measured over a distance of
only a few meters.)  The coldest part of the soil, and the most favorable
location for ice, thus is fairly shallow -- meters to tens of meters --
just deep enough for daily and seasonal temperature changes to damp out.

Near Mars's equator, there just isn't *any* depth that's cold enough,
unless current thermal models are not just wrong but very wrong.

The problem on the Moon is, where does the water come from?  There is
clear geochemical evidence that early in its history, the Moon was most
thoroughly baked; water surviving from before then is implausible.  The
only likely source of water is more recent impacts, and the only place
where it would be stable for any length of time is near the poles... just
where LP detected buried hydrogen.

>Lunar prospector may not detect very deep perma-frost layers thus with the
>Moon being a cold core body (and possibly Mars) ...

The Moon's core, while not liquid, is not cold in any absolute sense;
see above.  It's very unlikely that Mars's is either.  When a planetary
geologist talks about a "cold" core, that's a relative term, not an
absolute one.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)